Biasing Single-Ended Amplifier Output Tubes: A Basic Explanation and Demonstration

[@CC-te5zf]

And this is when the light came on for me - no pun intended. You can read forums for hours, observing well intended people argue back and forth. It becomes a battle in my mind between trying to grasp the information itself and then sorting thru the emotion to see if there's a consensus of some kind buried in the arguments of the "experts." Save yourself weeks, maybe months, of forum scrubbing and please just watch this video. The Air Force paid good money to send me thru electronic principles and I still have a massive 3 ring binder full of my notes, but none of that helped me as much as this video. Bravo - well done my friend! Thank YOU AGAIN! *And my Champ thanks you too. 👍

[@UncleDoug]

Wow....thanks so much, Chad. We're really glad to hear that the video was helpful :)

[@steveoroudy5590]

I appreciate his ability to explain things in a way that’s interesting and easy to understand.

[@UncleDoug]

......and I appreciate your nice comment. :)

[@Noah-gq7pq]

military training is best,,you know your shit ,you forgot more than i know

[@Idontwantthis2023]

Uncle Doug's videos are a masterclass collection, I love watching them and learning. And then there are quotes like these: "the last thing you want to do is die, while you're trying to bias your single ended amplifier"..

[@UncleDoug]

cmpmuller Greetings, CM, and thanks for the very kind words. Rusty and I are glad you enjoy the videos. I guess dying is indeed "the last thing" we'll ever do.....it would just be a shame to hasten the process ;)

[@jmg9808]

Uncle Doug toujours clair Net et précis! Thanks !!!!

[@frank1623]

c'est absolument la vérité

[@iangray7410]

I'm wondering if anyone has systematically assembled his videos to construct a primer on all things amplifier for the beginner ? I have begun such an endeavour, but KZbin seems to revel in scattering stuff all over the map. Here's what I've got so far (unedited): UNCLE DOUG NOTES How Tube Amps work ‑ HOW THE AMP WORKS 1,2 kzbin.info/www/bejne/rma2hH6ObJl3gck kzbin.info/www/bejne/b2GUmpSGi7utj5I TONE STACKS 1,2, kzbin.info/www/bejne/eJLXqHePe69sq8k kzbin.info/www/bejne/q4urfmh4rLV_iNk CATHODE BYPASS CAPACITORS kzbin.info/www/bejne/fqPOioiGoqqIns0 OSCILOSCOPE BASICS 1,2 kzbin.info/www/bejne/q5aypqNjjaeYrrc kzbin.info/www/bejne/i6TanIB-gJdqfJo OSCILOSCOPE AC/DV TRACING, RMS OUTPUT MEASURING kzbin.info/www/bejne/hp65omqEgdtmZ9U TUBE REVERB 1,2,3,4 kzbin.info/www/bejne/e4uppodqoc5_d9k kzbin.info/www/bejne/aXyomoR4lr6NesU kzbin.info/www/bejne/rYXahZaggr6hd7s kzbin.info/www/bejne/ppu3oZyHfJKirJY IISOLATION TRANSFORMERS kzbin.info/www/bejne/a4TNh6Bjp6tmb6M TRANSFORMER IMPEDANCE RATIOS kzbin.info/www/bejne/a5u4mqemocibpc0 CAPACITORS IN AUDIO CIRCUITS kzbin.info/www/bejne/ol7YaX1jrs1skKM kzbin.info/www/bejne/b4a4fatpYs17rJY kzbin.info/www/bejne/j4mmmZylg6hohLs RESISTORS kzbin.info/www/bejne/gnPXoJSomJuBotU kzbin.info/www/bejne/bqPYq6F_fdqbba8 kzbin.info/www/bejne/h3erlKCJiZx0kJI kzbin.info/www/bejne/hYPNpIaclsdlbZo kzbin.info/www/bejne/iqe0iItmgpubgLs POWER TRANSFORMERS kzbin.info/www/bejne/g4nKeGBmgq51faM PT BASIC DESIGN AND FUNCTION kzbin.info/www/bejne/nnvWgYSads2HobM GUITAR AMP VACUUM TUBES kzbin.info/www/bejne/jqCXn4mgn5mBiac kzbin.info/www/bejne/kJnCZmSIhZmJbKs PHASE INVERTERS kzbin.info/www/bejne/i2elqmZni56ZetE BUILD A CURRENT LIMITER kzbin.info/www/bejne/rYOpg6qFo7GmkKs HUM AND ITS POSSIBLE SOURCE kzbin.info/www/bejne/faO5pYtmhqyBotU BIASING DOUBLE-ENDED AMPLIFIER OUTPUT TUBES, PART 1: BASIC EXPLANATION & METHODS kzbin.info/www/bejne/rWqlYYWep8SMY6c

[@daleburrell6273]

...thats a GOOD one all right-!!!

[@KenjiKitahara]

I am going through these videos slowly (about one every 2-3 days) and they're helping me get through these days, while educating me at the same time. You're a great teacher, and I appreciate you sharing your knowledge. Thanks Uncle Doug! :)

[@UncleDoug]

You're welcome, Kenji. Thanks for watching :)

[@eddejager2007]

Thank you very much for your videos. You explain things so clearly that even people that don't have English as their first language can understand everything very well.

[@UncleDoug]

You're welcome, Ed. Thanks for your very nice comments.

[@denouch358]

Uncle Doug, thanks for putting up this very helpful video. I refer to it often.

[@UncleDoug]

You're welcome, Denis.

[@kneedeepinthedoomed]

Uncle Doug, I completed this procedure successfully today without incident, thanks to your excellent teaching. When I measured 450 volts after switching on my Vibro Champ, I felt a good amount of respect, but I didn't quake in my boots because I had watched your video. I did the measurements for several 6V6 tubes and found the newer ones (JJ) were running much hotter than an old GE tube (which was at 12.5 W with the original biasing). I also liked the overall sound better with the GE, so left it in there. Once I have to switch to JJs, I will have to rebias the amp because they're running at 15.5 - 16 watts of plate dissipation. I know how to do that now. The measurements were interesting. I also took the opportunity to glue the tolex back down and polish the front, using methods I learned from your videos. The amp is shiny and sounds great. I'm using a step-down transformer with this US-made amp, since I'm in Europe. I ran into some interesting polarity issues with that. If one turns the (Schuko) plug the wrong way around, the step-down transformer outputs 234 volts instead of 117. Not very nice. I believe many people aren't aware of this. I got myself a model with a polarity check so this doesn't happen anymore (it didn't hit the amp, I measured first). What is the result of running an amp made for 117 volts on 234 volts instead? I wonder.

[@UncleDoug]

Greetings, KD. A PD of 12.5W is still excessive and 16W is crazy. I tend to keep the cathode-biased 6V6's at around 11W. If 115VAC input can produce 450 plate volts, then 234V would yield close to 900 PV......which would breach all the capacitors and destroy the tubes.

[@kneedeepinthedoomed]

@@UncleDoug I guess I might change the resistor then. I suspect previous owners in Europe didn't pay any attention to the plug orientation, so I'm surprised the amp still works and nothing looks destroyed inside... I should probably measure all the caps, though.

[@UncleDoug]

@@kneedeepinthedoomed Plug orientation is a safety risk but does not threaten the circuit components, KD. Increasing the bias resistor value will result in better tone (in my opinion) and longer tube life.

[@ronniepirtlejr2606]

"It's a real Downer when your heart stops!" Lol, I have to agree Uncle Doug!

[@UncleDoug]

Trust me, it's scary as heck, especially when you feel it struggling to regain its proper rhythm.

[@Tonetwisters]

@@UncleDoug I had A-Fib for six years. THAT is like an earthquake going off in your heart, and it is horrifically miserable. Got that fixed. Now I just have six blown discs in my lower back. It's been a good past 15 years ...

[@VitalikButtring]

Years of confusion cleared up in 20 minutes.

[@UncleDoug]

That's good to hear, Jan :)

[@fullwaverecked]

@@UncleDoug Amen to that.

[@ivanmilenkovic4324]

This is the best explanation on biasing I've ever found on YT.. and the whole Internet..

[@UncleDoug]

Thanks, Ivan. One change is that it's better to measure the plate voltage between the plate and cathode....not ground.

[@ivanmilenkovic4324]

So the actual plate voltage is voltage at pin 3 minus the voltage drop value?

[@UncleDoug]

Yes, I guess you could look at it that way.

[@ix-Xafra]

Uncle Doug, I wish you'd been one of the instructors when I through tech school!! Thanks bloke!!

[@UncleDoug]

I wish I could have been there for you, Vinny :)

[@ix-Xafra]

@@UncleDoug well you're here now and digital communication allows us to be in contact. I quit working as a technician 30 years ago. Digital technology made myself a thousands of other guys redundant. I worked maintaining telephone exchanges which were mostly relay switch operated. I also worked on big dc power supplies and have melted a few tools - lol

[@UncleDoug]

@@ix-Xafra We retired guys have to keep busy :)

[@andyreevesarchive528]

Just wanted to thank you for your awesome videos! An electrical engineer friend of mine (guitarist, electronics tinkerer) recommended your channel as the best way to learn tube amp electronics--he was totally right. You're a fantastic educator.

[@UncleDoug]

Andy Reeves You're welcome, Andy. Rusty and I are really glad to hear that our videos have been helpful and informative. Thanks for watching :)

[@diy-speaker]

Thanks to you, i've build 2 amps for my self. One SE and one PP. You've opened a whole new world of me.

[@amoruzz]

Good information Doug. Safety, safety safety.

[@UncleDoug]

Thanks. Yes sir, Amo :)

[@johncarlisle3076]

Hi Doug, this is the first comment I have ever posted. I wanted to thank you for this video and the follow-up video. I have been playing guitar for 30yrs and during the last few years learning about amps. I had found it very hard to find a thorough demonstration of the biasing procedure even though I understood the theory around it. Its really good that someone with your experience is posting this type of experience. Warm regards John C

[@UncleDoug]

You're welcome, John. We're glad the videos were clear and helpful :)

[@dembydish]

Very helpful. I am writing notes as I watch to keep this all straight in my head. Have been away from tube amps for a while, so it's good to refresh. I learn more each time I visit.

[@doogsm6013]

Hi Doug: I was about to correct you on a couple of points but I read the description and see that you cover them in your notes. Excellent tutorial and WOW what a clean little Gretsch! Usually the ones I've seen have been shall I say "faithful companions". Cheers Mike.

[@UncleDoug]

Thanks, Mike :)

[@tomg3122]

Thanks Doug, helped save my StewMac Champ project. She was running way too hot from the get go.

[@UncleDoug]

I'm glad the video was helpful, Tom.

[@JC-11111]

Apparently my little Monoprice 15w is set cold. It's got a test point and adjustment pot inside, from what I understand. Headed to watch the double ended vids next in hopes of learning to check and adjust mine. The last post I found at TDPRI said this guy's was around -5.86v and he set it to -12v but I'm not just going to accept that as correct until I learn how this all works and whether it actually is correct for 2 EL84s Edit: so I found the schematic and it plainly says 'set to -12.5V' at the bias pot. So I guess that settles that?

[@Noah-gq7pq]

excellent doug,,this is the best i have seen,,i worked in electronics production,but i forgot all this stuff,,now im ready to get in there and test my amp,,i want a warmer sound and mabey this amp is set different,,thankx again do more old school electronics,,no one knows much about this stuff in the computer age we live in.

[@UncleDoug]

You're welcome, Noah. Good luck.

[@treborheminway1196]

You should be a pro narrator for a wide range of educational videos.

[@UncleDoug]

Thanks, Trebor. I would love the opportunity.

[@Paulbunyanman]

Doug you hit it out of the park. Love your videos. Great explanation of the process

[@UncleDoug]

Thanks, Paul. That's great to hear :)

[@ivanaiguana]

your videos are gold for all of us. thank you very much.

[@UncleDoug]

Glad you like them, Ivan :)

[@daleburrell6273]

This video brings back a lot of memories of back when I was a U.S. Navy electronics technician...it has been a long, long, time since I worked on any tube type equipment(!)

[@UncleDoug]

We're glad to help you reminisce, Dale. Please watch more of our videos.

[@anthonyduncan2425]

Well I have watched this a few times and I'm starting to get it. My 6V6 on the 9002 is perfect and removing the strange air gap resistor caused the thing to just start working. I am amazed, I actually fixed this thing... ;) Thank you Doug

[@UncleDoug]

Congratulations, Anthony. This should give you confidence to continue your new career in amp repair :)

[@tonyhills2112]

I find myself referring back to your videos often. You’re still the best Doug! 🥇

[@UncleDoug]

Thanks so much, Tony :)

[@el_wumberino]

I am not into guitar amps; the plan is to build some HiFi tube amps, but principles stay the same - please correct if am wrong. However, your videos do help me understand what is going on in those circuits, how the electronic parts work and why. At school was I never really interested in physics (… it's just stuff that happens to some other stuff and it'll still happen without me understanding it …), but now, I want to know about it, and your videos do help a lot, they're epiphanic to me. Thank you very much for your effort in spreading knowledge in such a comprehensive and kind way. Please give your four legged companions an extra treat from me!

[@UncleDoug]

Thanks for the very nice note, EW. Yes, the fundamentals are all the same. We're glad the videos have been helpful. Best of luck with your projects.

[@_David_E_]

Thanks Uncle Doug, this is the clearest explanation of cathode biasing of single ended amps that I've found so far. I really like the way that you explain things. I know have a much better understanding of biasing and it's relationship with headroom.

[@UncleDoug]

Thanks so much, David. I'm glad to hear that the video was informative and helpful.

[@stephatoms9801]

Hi Uncle Doug, Thank you for the video. I am an electrician and guitar player. Loved watching ohm's law in action. Your safety measures and explanation were awesome. You have renewed my fascination with electricity. Thanks again. You have a new fan.

[@UncleDoug]

Thanks, Steph. Welcome to our channel :)

[@keithblaney9064]

One of the things I really appreciate about these videos, besides the learning opportunity, is the fact that you leave your mistakes to be seen. The disclaimers and corrections are added later over the top. It greatly increases my faith in your presentation and adds to the humanity of the whole process. Good stuff.

[@UncleDoug]

Thanks, Keith. Unfortunately, KZbin has decided to eliminate any notes or corrections within videos. So I guess the mistakes will have to go uncorrected :(

[@keithblaney9064]

Yikes! (I know you will continue to make things right, in spite of ewetoob...)

[@UncleDoug]

We'll try, Keith. I will never understand the compulsive need to constantly modify systems that are working just fine.

[@straightlad1625]

Dear Uncle Doug, your videos are so informative and it's awesome how you explain all the basics and tricks, especially the biasing of a single ended cathode biased tube here. I have a small Randall RD 5 amp, it's nothing special, but it has a cathode biased single ended 6V6GT. I looked at the schematic and wondered whether the stock 470 ohms resistor was okay. So I did all the steps you explained in this video. I did all the measurements and the math and I found out that my output tube is running way too hot. The 6V6GT has a plate dissipation of almost 20 watts and a plate current of 57-60 mA. I tested three different 6v6 tubes and all three tubes had roughly the same result. I was really shocked that the stock 470 ohms cathode resistor is way too low, but it should explain the great heat and the strange and quick degrading sound of the amplifier. I have ordered a set of resistors with different values to find the best bias setup and thanks to your explanations, I can now bias the 6V6 properly. I really love your videos and your pets too, please keep up the good work. Many greetings to you and your cats.

[@UncleDoug]

Thanks for your very nice comments,SL. I'm glad the video helped you reduce the harmful bias of your output tube.

[@straightlad1625]

@@UncleDoug Hi Uncle Doug, I have to apologize, because I made a really bad mistake with my calculation. I call that a typical bad luck for a beginner. I measured all spots and calculated it again, found the bias is a little hot, but not as hot as I had calculated at first. It's about 101.4 %, but that's okay for now. Seems the designer of that champ style power amp likes it to be driven as hot as possible. Maybe I'll try a little higher cathode bias resistor than the 470 ohm, just to relive the tube for a longer life, but the amp works just fine. So please forget my nonsense I wrote before. Greetings to you and your sweet kitties !!!

[@UncleDoug]

@@straightlad1625 Thanks for the update, SL. We all make mistakes.....and learn lessons from them.

[@micheletobia1993]

Thank you!!! You are the best Amp Teacher

[@UncleDoug]

We're glad the videos are helpful, Michele.

[@robfpool]

Uncle Doug. This is just a general comment about all the videos you have posted. I was looking for a video on how to cover a speaker cabinet with vinyl and I hit 'Pay Dirt' as I want to build a small valve combo amp from scratch, but I have struggled understanding any electrical theory from books. The joinery side I am fine with Thank you very much for the most informative and easy to understand films I have watched in a long time. They are very inspiring. I have just watched your video on identifying the wiring on transformers so I am off to find a flea market that has old electrical items for sale. Rob

[@UncleDoug]

Thanks so much, Rob. Rusty and I really appreciate your very kind and favorable appraisal of our work. We're glad that the videos have been helpful and wish you the best of luck with your projects.

[@johngeddes7894]

Uncle Doug-I don’t have my RCA Radio Tube book yet, so these tutorials are essential to first pique one’s interest, then draw us in with some basics that don’t clutter our heads and obscuring our understanding in the process. Very skillfully presented. Getting close to pulling the trigger on the book!

[@UncleDoug]

Don't wait, John.....the manuals are readily available on Ebay and not expensive.

[@jimcastillo8950]

Hello Doug, I have a Vibrolux reverb custom amp which I converted to an eyelet board and have wired it like the AA964 schematic. Two weeks ago I wanted to check the bias to the tubes and found it cold, so I lowered my resistor value at the bias pot so I could get a higher current value and when I powered the amp I blew a fuse. Well when inspecting the circuit and chassis I found a piece of heat shield by the heater and pilot light section. This came off from above, I guess I caught a piece when pulling the chassis in and out. I then troubleshoot and found the power tranny was shorted. I then installed a vibrolux tranny that was a Weber brand and had to remove the end bell where the wires come out of in order for the tranny to fit. The amp powered on and my plate voltage was now 384 as opposed to the 430 volts I had on previous transformer. I like the lower plate voltage. I am running about 42 ma and using the power dissipation formula comes out to 16 watts for 6L6GC tubes. With the plate voltage running at 384 can I use the 5881 tubes? Thank you for you time and videos

[@UncleDoug]

Both the plate current and plate voltage are rather conservative for 6L6's, so I would say, yes, 5881's would be safe in this circuit. Simply recheck the bias with the 5881's installed and verify that the PD is within acceptable limits. Good luck.

[@johnjp5883]

Uncle Doug, I'm way in over my head & know nothing about electronics but I really enjoy your teaching & explanation. I play pedal steel guitar and appreciate a good amp my amp is a solid state Peavey Session 400 but a lot of players prefer tube amps. Your teaching gives me a better understanding when I listen to guys that work or have work done on their amps and just wanted to Thank you for these vids!

[@UncleDoug]

Greetings, John, and thanks for the nice comments.

[@MrBrymstond]

This is what people need to learn especially if they rebuilt the amp or if it's been used heavily... Great video

[@UncleDoug]

Thanks, Mr. B :)

[@jeffreyjhouser]

Doug, all of your videos are great but this one is fantastic! I can't wait to use what you've shown here in my own builds. Oh yes, great advice: "Don't die while biasing your tubes. It's a real downer!"

[@UncleDoug]

Thanks, Jeff. Glad you enjoyed it. Be safe !! :)

[@dwightbehm4747]

Thank you Uncle Doug for sharing your knowledge Uncle Doug without charge you've been very helpful to me your friend Dwight from AllenPark Mi. I'm 62 now but I wish I would have been a student in your class. Your worth listening to thank you for teaching the wright way. You R A presious. Joul. Thank You.

[@UncleDoug]

You're welcome, Dwight. Thanks for the very nice comments.

[@boulder89984]

How does one dislike Uncle Doug? Not cool. The man is a treasure.

[@UncleDoug]

Thanks, B, but judging from the fact that I always get some thumbs down.....granted they are from slobbering cretins.....would indicate that not everyone is a fan :)

[@austinpauxtataux8349]

One of your best ever Doug! U.D. reigns supreme

[@UncleDoug]

Thanks so much, Austin :)

[@doctorcircuit5338]

Wow 👍 I picked one of those up at the goodwill store for 7 dollars awhile back soldered the speaker wire's back on and cleaned the controls and it sounds great

[@UncleDoug]

That has the be the best deal I've heard of in several years, DC. Congratulations !!

[@doctorcircuit5338]

@@UncleDoug and it still has the price tag on it 👍 just couldn't bring myself to take it off

[@UncleDoug]

@@doctorcircuit5338 I don't blame you, DC. Why lose evidence of your major coup ??

[@neilzspam]

Another great video! Please continue.

[@UncleDoug]

Thanks, DN. I will start production on a sequel, probably detailing the biasing process for dual output tubes. Stay tuned.......

[@kolinevans9127]

Awesome info , I have a bit of learning of electronics and this is much more straightforward than other biasing issues, also more understandable, thanks.

[@thebuzztone]

I have to say this was fantastic information delivered in the most professional and entertaining fashion. I'm hooked !

[@UncleDoug]

+thebuzztone Thanks so much, TB. We have posted over 135 videos so far, so there are lots for you to watch :)

[@fullwaverecked]

Holy moley UD, I went to the URL you suggested and boy do I have a lot more studying to do. But at least I'm seeing a little light the further down this rabbit hole I go. Or should I say rabbit tube? It's like an alternate universe down here. The more you learn the more you need to learn... magic... And a little trippy too.

[@UncleDoug]

Indeed, if you really want to go into detail on topics like this, the depth of information is almost unlimited. You need to ask yourself.....how much do I really want and need to know ?

[@fullwaverecked]

@@UncleDoug I've said this before, and I'll say it again. Your advice is always spot on. At this point in time this is a perfect fit for me. I hobble around some, but I will soon get my ankles fused and after that I should be walking around normal. No worries :) until then I have some vintage test gear to work on and plan on repairing electronics for a living. Doing some of that already, mostly computers, but there is something about the sound of my guitar playing through that crazy Eico Signal Tracer... sounds strange good. But your right, this bunny hole is bottomless. So I've decided to focus only mostly on the Fender 5F1 & the Eico 147A schematics. So that is why I am very grateful for your first rate "tubetorials". Keep 'em comin! BTW I will be happily throwin down some well spent clams on your patreon as soon as I am able! Thanks again!

[@UncleDoug]

Thanks so much, FWR. Best wishes for a speedy recovery and good luck with all your projects.

[@antoniograncino3506]

Great intro video. The KISS [Keep It Simple, Shtupid] principle is a very good one. When is comes to math for electronics, it cannot be too simple for moi. Thanks to your well-presented tutorials, I am beginning to grasp and actually understand the mysteries and vagaries of audio electronics. Thank ya ver' much, Unca Doug Now, on to double-ended output biasing , where the fun really is.

[@UncleDoug]

Thanks, Antonio. We're glad the videos are helpful.

[@danielcua6506]

I am new to vintage tube amps and found this lesson to be of great value. I always wondered how one would modify an amp to have more or less "head-room". I always wondered what caused an amp to distort with manipulation of the electrical components. Now I know, thanks to Uncle Doug. I really appreciate your lessons, videos and topics covered.

[@UncleDoug]

You're quite welcome, Daniel. It's great to hear that the videos are helpful :)

[@judeconig9324]

Hope this is not getting redundant, but thank you so much for all these great videos. I/We really appreciate your love of teaching, and all the little gifts you give us!

[@UncleDoug]

Appreciation can never be too often received, Ken :) You're quite welcome.

[@colvinator1611]

Very well presented Doug. Thanks a lot, Colin UK 🇬🇧

[@UncleDoug]

You're welcome, Colin :)

[@joemcgraw5529]

very valuable information here ,my therory and basic electronic training is starting to come back and make sense ,been 28 years but thats ok wont work on any of my projects until im well informed and have proper instruments to do it safely and proper

[@UncleDoug]

Take your time to recollect all the safe-handling rules, Joe......then best of luck with your projects.

[@jrrustad]

Just turned on to UD! wow, Doug these are the Feynman lectures on valve amps! Thank you!

[@UncleDoug]

Glad you enjoy them, JR :)

[@petarbursac76]

The best educational videovI have ever seen. Thanks Doug. I have built 3 amp learning from you.

[@UncleDoug]

That's great news, Petar. Keep up the good work.

[@wtangodelta1715]

Thank you Uncle Doug A million times over! I've been ignoring this subject matter for 30 years for 2 reasons; at 13 years old I had better things to do, like learn my instrument (guitar). Now that I've kinda done that, I'm obsessed with finding that tone that gets to me down real deep and you are helping me understand how and why I'm on my quest and believe that I'm closing in on it.THANKS HOMEBOY! Now I'm one step closer to having a meaningful conversation with the other UNCLE, the one and only legendary "UNCLE ALBERT" here in my home town of INDIANAPOLIS. Some of you out there may have heard of him (heh heh heh) Thanks again Sir!

[@UncleDoug]

You're welcome, WT. Give UA our regards :)

[@wtangodelta1715]

Will Do UD! Might you inform us (if you can)a tad bit about U. A.'s recently patented 'Del Ray' tube amp? He told me he made 25 of them, all 10W amps, 8 or 10"(not sure which) with 'plenty of headroom" for my cleans. I could not get the $ quite fast enough, but I MUST have one. I WILL have one! HEHEHEHEHE!

[@UncleDoug]

Since they are so hard to get, WT, it sounds like you have a better shot at getting one than we do.....so if you do get one, please let us know what you think of it.

[@wtangodelta1715]

Will do UD- I will call UA first thing after he opens and ask (cross your fingers!) if he will let one go to me IF HE Has one. Very least Ill get more specs. Might get the link to the schematic. Peace on Earth okay? Later!

[@TheGasWoks]

I use to dislike electronics, but I needed to know more and more. Lucky for me I found your channel. Now I find it interesting and intriguing and have already carried out some successful repairs. I would like to build my own amp someday, but I am a long way from that at the moment. Thanks for sharing all your knowledge.

[@UncleDoug]

You're welcome, GW. Best of luck with your continued study of electronics.

[@TheGasWoks]

Thanks, you explain topics really clearly, it's amazing how you improve circuits and your knowledge of electrics seems endless. I have learnt some really interesting topics here on your channel about tubes, love it. Having said that it remains a little abstract thinking about what electricity is and how it travels through copper wire. Hats off to Tesla!

[@joeyscott4299]

Excellent Video ! Lots of great information . Thank you Uncle Doug

[@UncleDoug]

Glad you enjoyed it, Joey.

[@PracticallyFixed]

Hello Uncle Doug. Thank you for this excellent tutorial. I gave you attribution for this in a video I did where I used this method to check the bias on a IF Amp tube in a '53 Chevy Radio (Part 6). Just wanted to let you know I let everyone know where I got the technique, and a link to this video. Thanks again. [edit: spelling]

[@UncleDoug]

We're glad the hint worked for you, PF :)

[@bijaymalakar2639]

Great video with very simplified explanation. Been trying to understand this topic for a while, this is the best video that i have come across so far.

[@UncleDoug]

Glad it was helpful, Bijay.

[@kevinsvpbiscayne]

Very good explanation on this Output Tube Biasing Uncle Doug. This makes it much more clear to me. I even built a Current Limiter for testing amps now. All such great information. I really enjoy all these videos. I recently repaired a Capacitor issue in a vintage Trend LR19952 - 801 5 watt Guitar amp made by Pine Electronics Products co. LTD Montreal. They were built in the late 50s up to the early 70s out of surplus electrical parts. There is no input transformer but uses a 35W4 Rectifier 12AX7 input & a 50C5 output tube. 8"speaker, 3 input jacks, Tone & Volume control & a 2 prong cord. The Chassis Ground actually operates with 39 DC volts. It actually sounds pretty good for a vintage small amp. I can send you a schematic if your interested & pictures. Thank you kindly.

[@UncleDoug]

What would happen if you earth grounded the chassis with a 3-wire power cord, Kevin? If the circuit still functioned, most do, this would greatly lessen any shock hazard.

[@kevinsvpbiscayne]

I actually tried earth grounding the Chassis & then I received a loud hum over the speaker. So I measured the Chassis to have 37 Volts DC. I guess it is the way it is designed. Quite different from traditional amps I can see from your various Schematics you have illustrated. I am careful with the amp & only use it in the living room on the carpet. My uncle gave it to me when it had the Capacitor Hum issue. The Guitar store told Him to ground the Speaker Chassis to the ground on the cord but no improvement of course. They did not want to repair such a vintage tube amp & sold him a new one. lol I discovered it had a paper unicap containing a 50 mfd 30 mfd & a 20 mfd on a 150 Working Voltage. I had to wire 3 independent Capacitors in as they do not make the 3 in one capacitor any more that I could find. I removed the extra Ground Wire from the Speaker Housing as it was not designed to be there & then sounded better yet. Sounds good now with only a very minor hum that is likely normal to its design I believe. Thanks for your interest & reply. I tried cut & pasting the Schematic to this chat box but does not work. Thanks Uncle Doug & now going to watch your Part 2of Grid Biasing double Ended Tubes. Take Care.

[@UncleDoug]

@@kevinsvpbiscayne Thanks for your follow up, Kevin. Good luck with it and your other projects.

[@iangray7410]

What a fabulous lesson! I really like it because it offers constant safety reminders, an easy-to-follow, logical procedure, AND it explains how to voice (in part) an amp for more or less distortion. (Hope I'm not over-simplifying). Thanks Uncle Doug ! I'm feeling even more ready for my amp build with Bruce Egnater on Saturday coming.

[@UncleDoug]

Thanks, Ian. I hope your amp building session is a total success.

[@iangray7410]

@@UncleDoug I'll do my best to remember your tip about one hand only in the chassis. I can be impetuous and would hate it if my darling wife had to travel to a Detroit suburb to collect my ashes.

[@UncleDoug]

Yes, it would be a shame to have a good viewer, like you, incinerated, Ian. So for heaven's sake be careful :)

[@daveanderson6323]

Wow!... I love that Gretsch. This video is special to me because I damaged my Fender HotRod Deluxe trying to dissipate the Caps. I still have to fix it too! Not having an alligator clip for support, I shorted on other components causing a bit of smoke...I think the output transformer. Thanks to you though, I no longer feel all that concerned - worst case scenario, I gut the chassis and handwire a new amp. Cheers from Ontario

[@UncleDoug]

Wow......I hope a complete rebuild isn't necessary, Dave. Best of luck.

[@W1RMD]

I really enjoy your videos! Great slow speech and thorough explanations without being too slow and never boring. I've built a similar amp using a 6L6 driven by a 12AX7. I'm using solid state rectification and resistors for voltage regulation- no chokes, just simple. The output transformer is rated at slightly higher plate impedance than what this tube is rated at using 292 volts on the plate. It dissipates about 11 watts bias and sounds great! I can't seem to find many 6L6 single ended amps.

[@UncleDoug]

Thanks, Ryan. I too have found very few SE 6L6 circuits. A PD of 11W is rather low for a 6L6 in fixed bias and real low if cathode biased.....yet it sounds good. That's the most important criteria ;)

[@W1RMD]

@@UncleDoug I only used the 6L6 because I bought several at a yard sale for 50 cents each! I'm curious how it would compare to a 6V6. I didn't have any until yesterday I bought a Challenger HF8A which uses a pair of 6V6's in P.P. Can't wait to get started on the 1950's gem!

[@MichaelLloyd]

I have the 6156 version of the amp in your video. After watching the video again today I thought, what the heck, lets measure the plate dissipation. I followed your directions except I measured plate voltage across Pin 3 and 8, and came up with very similar numbers as you did. Plate dissipation is slightly lower at 11.28W. Here's the funny part. I've watched this video before but sometimes I like to watch informative videos like yours more than once. I have a schematic in the bottom of the amp. Guess what I wrote on it (last winter?)? Plate dissipation calculation values, except I used the method you used in the video. I came up with 11.87W that way. :)

[@UncleDoug]

Measuring the plate voltage between the plate and cathode, as you did, is the more accurate method, Michael, and will give you a slightly lower PD than measuring from plate to ground as I did in the video.

[@pcollenyt3683]

@15:33 > Tube plate dissipation is calculated as follows : (Vp - Vrk) x Ip. Uncle Doug measured the plate voltage to ground as Vp, but did not subtract the voltage drop across the cathode resistor , Vrk = 14.8 volts . So the Vp used was 14.8 volts too high. Using the corrected plate voltage Vp of (approx) 296 - 14.8 = 281 Vdc shows that the tube is biased at 281 Vdc x 0.0415 mA = 11.66 watts. This video was an excellent presentation, aside from this error.

[@UncleDoug]

Thanks, PC. This was a very basic presentation. In all subsequent videos the PV has been measured between Plate and Cathode......even though it only matters in cathode-biased amps ;)

[@j.w.8663]

Many ppl have harped on this point but U Doug DID actually explain this in a 'roundabout' way at @18:32 in this video where he mentions that he measured across the cathode resistor (meaning from plate and over the cathode resistor) and thus the calc with a higher voltage will err a little on the pessimistic side, showing a slightly higher pwr dissipation than it really is. This means you won't be tempted to run the tube at the max limit. 😁

[@djfrank59]

Hi Doug! I like the way you explained cathode bias! I need to show this video to some of my customers...I have a tendency to forget that almost everyone I explain bias to is NOT a technician...I always forget and think I'm talking to another tech (LOL)...If the amp you used in the video wasn't a collector's piece, I would say you could install a potentiometer to vary the cathode bias, which would make it a lot easier to tweak when replacing the output tube...I've done that to many newer single-ended amps with fixed bias...I've also used extra resistors to limit the pot's range in some cases...Keep up the good work and pet Rusty for me :)

[@UncleDoug]

Thanks, Frank. Rusty sends his regards. I agree with the benefits of installing a cathode bias potentiometer, in fact I posted a video about the "adjustable bias" concept a while back. In this case, as you said, I didn't want to alter what was otherwise a pristine original amp.

[@DChrls]

Very educational video on biasing an amp. Thanks, I now feel comfortable in checking/adjusting tube bias on my BF and SF VibroChamp's, A good way to think of the bias resistor, for me, is to think of a dimmer switch for a light bulb. Increase resistance dimmer bulb= lower output, decrease resistance brighter bulb= higher output.

[@UncleDoug]

You're welcome, OAG. You're right, the Plate Current is indirectly related to the bias resistance.

[@DChrls]

@@UncleDoug I have a question for ya. My Blackface VC is alot darker sounding than my early 70's Silverface VC. The Silverface does have a Pyle Driver speaker, model MH810, in it. Other than that and new Tung Sol tubes both have all original components. Is that normal between the BF and SF VC?

[@DChrls]

Well I finally gave the Blackface VibroChamp a good going over to find out why it is so dark sounding. The problem is the speaker cone is shot, kaput, finished. Guess it's time to order a Weber 8A125

[@gregedenfield1080]

Thank You! Love Your Teaching! You Are The Best!

[@UncleDoug]

Wow.....thanks, Greg.

[@stevecraig7643]

I just found you the other day. Im loving learning about tube amps. I would never try this at home but its fun to know how the things work. I have a marshall DLC5 , fender blues jr and a boogie mk5 35. cheers

[@UncleDoug]

Welcome aboard, Steve.

[@SandersAmps]

Fantastic class. And yes, I don't want to die:). Thanks Uncle Doug. And boy, do I hate math, but this was easy to follow.

[@UncleDoug]

You're welcome, Shaun.

[@memorypalace8009]

Thank you for taking the time to explain all this.

[@UncleDoug]

You're welcome, MP :)

[@a1s2d3d4]

I haven't read all comments. Maybe somebody noticed before me, but: If you measure current thrugh cathode resistor, you actually measure sum of all currents in the tube. Cathode emits electrones and they go somewhere -> as your tube is 6V6, it's tetrode so you have measured Ia+Ig2 (anode + grid #2 current). Not only plate current as you said. So you have to subtract: Ia=Ik - Ig2 As you don't have resistor in series with g2, disconnect it from supply and measure with amper-metre. Than subtract. g1 (control grid) doesn't pull any current as long as it's on lower potential than cathode. It will drain some current if we had cathode follower before it and driving grid with positive signal. (Not for guitar but hi-fi) Plate dissipation: Pa = Ua * Ia -------> Ua=anode (plate) voltage=voltage between pins 3 & 8, not 3 and ground, as cathode is raised +14.84V above ground; Ia = Ik - Ig2 That's it.

[@UncleDoug]

+Ivan Horvat Yes, Ivan. The cathode current does include screen current and to be completely accurate, the SC should be subtracted and multiplied by the PV from plate to cathode to determine the PD.......but recall that this was a "basic" video and I chose to simplify the process. By using the cathode current times plate-to-ground PV, the PD that results will be a bit high, providing a safety factor for beginners. Thanks for your input.

[@scottmclennan692]

yes this was a really informative vid for me. i have a hand made Purdy "tramp" and changed the power.tube in it. the manual says i dont need to get biased but does run hot aftef a few hrs playing. breaks up around 6 on the volume. i might just take it in to a pro and see where the voltage is really at. thanks Doug :)

[@UncleDoug]

You're welcome, Scott. If your amp's output tube is cathode biased (check the literature or ask the builder), then it probably does not require re-biasing......but, if it's fixed bias (the cathode is grounded, which is quite unusual in single-ended amps), then a new tube must be re-biased.

[@dainhuston]

This is great my understanding expand 's every time I watch one of Uncle Doug's video 's

[@UncleDoug]

That's our goal, Dain. Thanks !!!

[@redfishbum]

Outstanding video. Thank you so much. I just built my first champ from a kit. You're helping understand so much. I can see how addicting this can be. Bart

[@UncleDoug]

redfishbum You're welcome, Bart....glad the video was helpful. A Champ built from a kit is a great way to start what may soon become a very addictive hobby. Welcome aboard :))

[@stepsofashaman...4283]

wish you had a tube amp builders class... oh wait, this is it. good video... coincidentally I had a scare with a small arc.. discharge your caps folks....

[@UncleDoug]

Thanks, Jason.....and good advice :)

[@briguyhackins]

One of the best clear vids I have ever seen. Thanks Doug

[@UncleDoug]

You're welcome, B :)

[@carloshugo.almeida]

You are the man, Doug! Thanks..

[@UncleDoug]

Thanks, Carlos :)

[@jackallen6261]

"I've got one hand ion my pocket..." and the other one in an amp circuit! Ok, I'll see myself out now, lol. Thanks UD!!

[@UncleDoug]

Make sure it's YOUR pocket, Jack.

[@oneofthemodels]

Uncle Doug once again great video thank you so much I hope you know how much you are appreciated for what you're doing for us noobs out here you are the coolest of the coolest

[@UncleDoug]

You're welcome, MM. Thanks for your very nice comments.

[@catdumpling]

i concur, another awesome video! it's great to finally see one on cathode biasing, rather than the typical Fender trim-pot videos (which are a dime a dozen.) i started a new thread and reposted the video over on the TDPRI amp forum: i think it'll help out newcomers quite a bit, since SE cathode biased kits are so popular, as well as stuff like old Champs scored off Craigslist and that sort of thing. can't wait for the next one!

[@UncleDoug]

Thanks, Cat. It's always good to hear from you. I think the next installment will be cathode biasing with dual output tubes. It's much the same process, but with a couple of extra steps. I also hope your Melodier project is going well.

[@catdumpling]

Uncle Doug my computer decided it needed a new hard drive, so i had to put off getting my transformers for a couple weeks. minor setback and no big deal though. who knows, maybe i'll get lucky and Triode will have some sale prices coming up (i can always hope ;) .

[@UncleDoug]

I never recall seeing any sort of sale prices from Triode. It's too bad that Musician's Friend doesn't sell transformers.....

[@catdumpling]

yeah, probably just a bit of wishful thinking. the combined price of the ones i'm going to get is only around $75, so it's still a great price!

[@UncleDoug]

Transformers are always a major expense in any amp project, but if you get them from Triode, it's less painful than from other sources. Also, If you get them around Christmas, they'll be a nice gift (to yourself)......way better than a lousy pair of socks or underwear.

[@Jesuswinsbirdofmichigan]

Ouch! my 40W (prowler) made an "impact" in the past; glad to be alive/learning now!!!, thx, bird.

[@UncleDoug]

You're welcome, Steve.

[@theot71]

Very comprehensive and clear description. I had the miss conception that biasing was for matching pairs of power tubes and therefore, single power tube amps did not require biasing. I own 2 amps and don't use them regularly, should biasing be checked periodically or when replacing tubes. I am assuming the sound quality will indicate when tubes need replacing.

[@UncleDoug]

Thanks, Theo. To be honest, most cathode-biased output tubes (which are in virtually all single-ended amps) are probably not in any great danger from incorrect biasing, since they tend to "self-correct" and protect themselves from harm. It's a good idea to check their bias every year or two (or whenever you change output tubes) to see if the biasing resistor has changed value over time (especially if they are old amps), but otherwise, they tend to be "low maintenance". Fixed bias output tubes (with grounded cathodes) are another story. They do need to be checked at regular intervals and definitely rebiased whenever a tube or tubes are replaced. If you have a double-ended amp and are not sure what type of biasing it utilizes, I can tell you.

[@r3tr0nic]

I seen my observation has already been commented on (calculating the valve's dissipation including the V-drop of the cathode biasing resistor vs cathode-plate V-drop only), but I agree with you that it is a good way to give yourself a safety cushion/margin! Valves are way before my time and I never learned much about them in university. If I imagine this correct, using the current flowing through the plate connection and the voltage measured from cathode to plate, it would pretty much get you the majority of the power dissipation. Thinking like a road, the traffic all originates from the cathode, and most exits via the plate, but some diverts to the screen grid. At least, I'm thinking this in Kirchhoff's Laws. As an EET, it certainly is interesting getting myself acquainted to valves and how things used to be before SST came about and comparing the different ways things were achieved :)

[@UncleDoug]

Your analysis is correct, Salcon. I now am careful to measure PV from plate to cathode in cathode-biased circuits.

[@gapguy9564]

thank you for taking us through...

[@UncleDoug]

You're welcome, Gaurav.

[@jonnybeck6723]

Thanx for another great and instructive video/lesson... And, for me anyway the typos wind up forcing my brain to work a wee bit more, and odd though it may seem, the overall learning experience was enhanced... thanx again and cheers

[@UncleDoug]

You're welcome, Jonny

[@annomaus8386]

Another vy good tutorial. Here's my vote for a dual pentode (PP) bias video..tnx!

[@UncleDoug]

Thanks, Chuck. The video you requested was posted a couple years ago. Please check my video list for Biasing Double-Ended Amplifiers.

[@lego40404]

I'm so glad I found your videos, clean cut and to the point with laymans terms. Im hoping to build a BFPR soon for my next build and I loved your two recent videos on your BFPR

[@UncleDoug]

Thanks, Lego. I'm glad the videos were helpful. Good luck with your project.

[@johncunningham5435]

That is a great demonstration of biasing with this type of method. The only concern is that carbon resistors have a tendency to drift at +-10%. I normally find the resistance goes higher, even though your readings are well over the 330 ohms it still well within the 10% margin as ohms law demonstrated with the dissipation factor of 12 watts with that particular tube, nicely done.

[@UncleDoug]

+John Cunningham Thanks, John. I agree that carbon resistors have their limitations, but lots of purists stick with them in their quest for "vintage tone". I personally prefer metal film resistors, especially for screen grids and power supplies.....but in this application, the carbon resistors seem to work well.

[@johncunningham5435]

I just recently acquired a B&K 747 Tube Tester; the first thing I had to do was remove a handful of carbon resistors that had a tolerance of +-10% and were way out of spec. I ended up using metal film resistors that were rated at +-1%. On top of that endless amount of work went into it before calibration procedures could be performed. Yes! I do understand the nostalgia when it comes to preserving the original components, but in order to fix these amps accuracy is important along with reliability.

[@UncleDoug]

Yes, indeed. I tend to believe, however, that much of the so-called "vintage tone" that so many musicians seek is due to the variance from specs within the circuits of old amps. The sum total of all these variances yields a somewhat unstable and "dirty" tone that many people truly appreciate and seek to emulate. In a "great" old amp, the variances all work together.....but in some, they don't. Tweed Deluxes from the 1950's are an excellent example. Unmolested, most are rough, raw, and wonderful.....but if you replace all the carbon resistors and waxy caps with metal films and modern high-grade caps....they become much more sterile and (to many) less interesting.

[@elmakednos]

Great video.Anyone can understand everything.Thank you Uncle Doug.

[@UncleDoug]

You're welcome. Glad you liked it :)

[@Ronnie631000]

Excellent. Love this stuff. Yes... I am just learning. Keep on Rock`en! From Sioux City,Iowa.

[@UncleDoug]

Thanks so much, Ronnie. It's great to hear that the video was helpful. Best regards from UD & Rusty :)

[@toxicgraphix]

Uncle Doug for President! ... if only our politicians could explain things so perfectly. I think I'm really beginning to understand how guitar tube amps work ....

[@UncleDoug]

Thanks, TG. Stay tuned for more technical videos..... :))

[@iangray7410]

I reckon he and Bernie...but seeing as UD is from Texas...uh..just an idle fantasy.

[@frankscutari9516]

What a clear concise excellent job. Thank you so much

[@UncleDoug]

Thanks, Frank :)

[@frankscutari9516]

My first amp (used)was a Gretsch 6152 which has tremolo and Reverb. Years ago I removed the tubes because it was distorted at very low volumes and not knowing anything I thought one of the tubes might be bad however the 6V6 had broken the alignment pin because of age and I put the tube in one pin off. I bought a new rectifier and power tube and it would start playing very clearly for the very first minutes and then suddenly gets very hot and get distorted. So I shut it off and have not looked at it since. After looking at your video I was checking my 250 Ohm resistor and it crumbled in my fingers! There is the root of my problem. So of course I have a couple resistors coming in and I can't wait to replace it and see how it operates. Thank you so much for all your help.

[@UncleDoug]

@@frankscutari9516 I hope the new resistor solves the problem, Frank, but I wonder why the old one burned up. You might take a close look at your filter caps.....one or more may be shorted.

[@frankscutari9516]

Thank you Doug, I certainly will. have a good day

[@UncleDoug]

@@frankscutari9516 I hope so, Frank.

[@bullthrush]

Thank you, an excellent Video! Perfect timing too, as I am ready to start soldering a scratch built 5F1 with a solid state rectifier. Thanks again.

[@UncleDoug]

You're welcome, BT. I'm glad the video was of interest. Keep us posted on your project.....it sounds like an interesting one.

[@dr.strangevelo6031]

This was great. A very helpful refresher. And a new technique for me regarding measurement of the voltage drop. Keep up the good work, sir. (Also just a fun note - I picked up some parts off our local classified ad website last week, and the guy with the ad had linked to one of your vids as an example of a possible build using the parts. Of course I immediately recognized the Uncle Doug video. So just FYI, up here in Winnipeg total strangers are watching your videos, being inspired, and chatting about amps amongst themselves. Figured you might appreciate knowing that.)

[@UncleDoug]

Wow....thanks, Dr. S. It's good to hear that Rusty and I are now the spokespersons for a Canadian classified ad website. Today, Canada.....tomorrow the world :)) It's also good to know that people are chatting about tube amps. It's a great hobby and the more people who become involved, the better. Thanks again for a really nice comment :)

[@repairfreak]

Very well done video! I learned something new. I thought by biasing the output tubes hotter, or with more plate current would actually cause amp to break up or distort / flattop a sine-wave at a lower volume level. Thanks for your explanation. I’m next looking forward towards seeing how you bias a tube amp with two or four output tubes with 4, 2 or 1 variable bias resistor in a amp that doesn’t use a fixed cathode bias resistor for output tube(s). 🙂👍

[@UncleDoug]

Thanks, Mike. The chart in the video was a bit misleading and I corrected it with graphics that are not visible on all viewing devices. Hot bias does induce earlier breakup, and cool bias increases headroom. I apologize for the confusion. This was one of my earlier videos. My knowledge and techniques have improved with time and my more recent videos are far more astute. I have posted a video showing double-ended biasing, variable resistor fixed biasing, installing of a variable bias pot, etc. I hope you enjoy them.

[@ertreri]

these are the nicest videos. pen and paper first :)

[@UncleDoug]

Thanks !! Glad you like them :)

[@mendamp1715]

Excellent presentation, I will go home and try this soon!! Thanks, Uncle Doug!!

[@UncleDoug]

You're welcome, Eric. Be careful and best of luck.

[@ijamsum]

I do the bias on several amps without the math you know by using Webers bias calculator for class A/B or class A by switching his chart to class A ! I use a plate voltage probe and a grid bias probe to set the Webers recommended value at slightly lower value because voltage in my location varies - 123VAC to 116VAC at home ! You put your tube in the probe and plug the socket of the probe into the amp , first the plate voltage probe then bias using the grid probe setting my DMM to the probe instructions which is critical !

[@UncleDoug]

Whatever works for you, IJS. It sounds like you have a good procedure.

[@unhinged17]

Wonderful demonstrations and information as always with your videos, Uncle Doug. You make all these tube amp mysteries very clear to me, after struggling with understanding this material for years! Thank you very much for these invaluable videos, as cmpmuller said, they are truly a master class collection.

[@UncleDoug]

You're welcome, Jason. Thanks so much for your very nice comments :)

[@duanehawkins4783]

Doug I'm really enjoying these videos - very clearly presented and understandable. A couple of questions on this one: 1) I had the understanding that old tube amps with no ground were inherently unsafe but you are electing not to ground this one. Is it a matter of ensuring the 'death cap' is properly spec'd & functioning correctly? 2) Can you elaborate on the need for the lightbulb device? Cheers and thanks again! edit: I just found your video so #2 is answered :)

[@UncleDoug]

Thanks, Duane. With my own amps, if they are pristine originals, I keep them that way. When I sold the amp, however, I installed a 3-wire power cord and removed the "death cap".

[@unicorneggspam]

I really appreciate your videos. They are incredibly helpful in helping me to understand these concepts

[@UncleDoug]

You're quite welcome. It's great to hear that the videos are helpful :)

[@MrAletube]

The current you calculated is actually the sum of plate and screen grid. The voltage you need is plate to cathode,not to ground.

[@UncleDoug]

+MrAletube You're right, Mr. A. I have since corrected this oversight. Thanks for your input.