Eurotubes "Pro One" Bias Probe Evaluation.......Plus: Make Your Own Bias Probe

[@UncleDoug]

Ala Carte MENU: Plate Current vs Cathode Current @ 01:50 Proper SE Bias Procedure Discussion @ 04:35 Performance of Manual SE Bias Procedure @ 07:16 Performance of Eurotubes SE Bias Procedure @ 12:51 Comparison of Results for SE Amp Circuit @ 14:05 Manual Measurement of Screen Current @ 15:08 Open 1st Gift Box w/Jack & KC @ 16:39 Performance of Manual DE Bias Procedure @ 19:31 Performance of Eurotubes DE Bias Procedure @ 25:33 Comparison of Results for DE Amp Circuit @ 26:46 Open 3 more Gift Boxes @ 27:38 Final Discussion of Eurotubes Bias Probe @ 29:36 Build Your Own Bias Probe @ 32:08 Closing Statements @ 45:58 Car Show @ 47:27

[@kendavis8046]

Always a good day when there is a new Uncle Doug video.

[@UncleDoug]

Thanks, Ken :)

[@kendavis8046]

@@UncleDoug I retired this week, so now I have time to watch even more.

[@daleburrell6273]

@@kendavis8046 GOOD FOR YOU-!!!

[@Finom1]

Uncle Doug, that was a masterfully done educational video. We love your amp videos and you have such a unique eloquent way of teaching us all!!! Bless you and your family.

[@UncleDoug]

Thanks so much, F1. We really appreciate your kind words.

[@Starcrunch72]

If I could thumbs up this comment 100 times I would---thanks Uncle Doug!!

[@UncleDoug]

Wow......thanks, SC :)

[@zoltannemeth8864]

Great video! I had an electronics instructor years ago that had been working on electronics for many decades. Some sage advice from him: “if you accidentally or intentionally touch the input of a rectifier while the circuit has power, it instantly becomes a Rectum-Frier”.

[@UncleDoug]

I would think this would even more true if you actually sat on the hot wire :)

[@Earlvis]

A friend of mine used to own an amp repair business but closed a few years ago. He gave me a pair of these testers and they sure make biasing much easier. Thank you, Doug for teaching us that which cannot be found in any classroom today! I hope you are doing well, Good Sir!

[@UncleDoug]

You're lucky to have such a generous friend, Earl. So glad you enjoy our videos.

[@stevebeck3164]

The only suggestion I would make regarding making your own bias probe, is to chassis mount the tube socket, since output tubes can generate a lot of heat and wouldn't want to melt or singe the surface it rests on, and use recessed, isolated probe lead connections in same chassis to prevent inadvertent death sentence execution. As always, top notch teaching of tube theory, testing and appreciate you inviting us to your home, love of classic cars and pets. Miss Rusty.

[@UncleDoug]

Thanks so much, Steve, for your nice comments and your good advice.

[@jamesrobinsonjr.9384]

Thanks Uncle Doug, you're the best!

[@UncleDoug]

You'r welcome, James. Thanks !!

[@matthewjones8510]

Uncle Doug, a most fantastic specimen of human being. Thanks for your work and for showing it.

[@UncleDoug]

You are quite welcome, MJ :) Thanks !!!

[@waltertose3050]

Uncle Doug, Based on your posts I am pretty sure you are older than me by a few years, but wow, when I watch your videos do I ever connect with your "vibe", and I am guessing that there are thousands of others out there who feel the same. Please keep doing what you do. It is very educational and very important.

[@UncleDoug]

Thanks so much, Walter. I'm 73, and am glad to still be able to connect with the audience, instead of a rocking chair and Metamucil :) We definitely will continue for as long as we're able .

[@waltertose3050]

@@UncleDoug and I am 68 and a Fender-a-holic. Do you have any advice re my other post about the specifics of how to deal with my newly purchased vintage Fender Bassman?

[@rchavez2112]

THANK YOU David Freseto! (I hope I spelled that correctly). That was a very generous donation and I look forward for Uncle Doug to showcase your gifts. I can't wait for that Gibson Echo unit. Thank you Uncle Doug for another great video.

[@UncleDoug]

Amen, Rick. I have been working on the tweed Gibson GA-2RT and have it working nicely. Next will be the cosmetics......so stay tuned :)

[@monto39]

Great video. I got one of these, after waiting for almost a year for these to be back in inventory at Eurotubes. I think it was worth it though, as it's not easy to find one that reads plate voltage. Only other one I found was a kit that plugged into an existing multi meter. Now it's been sitting for almost a year and I never yet had the need to bias anything. Soon I have a '71 Super Reverb arriving though and I'm going to want to check bias settings for the (new make) Telefunken 6L6GC's I have set aside. I believe for this amp it would require changing a bias resistor (it has a balance pot but not a bias, if I remember right). This video is a great reference on using this probe. This channel is a great reference library on tube amp function in general

[@UncleDoug]

Thanks so much, M. We're glad our videos are helpful :)

[@mikealves3858]

The best channel in the whole internet! Thanks Uncle Doug!

[@UncleDoug]

Wow, thanks, Luis :) Our pleasure.

[@EngineeringVignettes]

Thanks Uncle Doug, good review of measuring for tube biasing. Cheers,

[@UncleDoug]

You're welcome, Eddy.

[@wynandvanreenen2612]

Your channel is gold. I ragequit building tube amps years ago due to the lack of this type of knowledge out there. I am dyslexic, but not stupid, and struggle to consume knowledge the conventional way. Your videos makes perfect sense to me and truly helps me understand the engeneering in circuit engeneering. I am so "amped" to build tube amps now! You realy lit a fire in my soul. As a guitarist, I love tube amps and owned many tube amps, mostly vox ac30's. Like 5 or 6 of them😂 I want to start with the 5f1 circuit and build a bunch of amps, untill I design my own circuit and build it. I saw in your comments on the "how amp circuits work" you had some uppety clever people twirl their mustashes, puffing their pipes, looking down at us common folk and corrected your " not 100% accurate" explanations. As a music teacher, I often have to take creative license to get someone to understand something on a basic level. Explaining it on an engeneer level is exclusive and counter productive to the non engeneer diy hobbiests out there. I love your videos and thank you from the bottom of my heart.

[@UncleDoug]

Thanks for your kind words, Wyn. We're glad the videos are helpful.

[@allthegearnoidea6752]

That’s a lovely gift from David. I have to say all my vintage radio friends have always been generous.

[@UncleDoug]

Indeed. I was overwhelmed by his generosity. I believe we have the nicest, most generous viewers on all of KZbin :)

[@jasonaustin3270]

I learn so much from all of your videos. Plus we get gut shots of some real gems. Thanks Uncle Doug.

[@UncleDoug]

Our pleasure, Jason :)

[@cass2771]

David, thank you! Your generous gift will bring hundreds (?thousands) of viewers more UD videos!

[@UncleDoug]

Yes it will, Cass. I'm working on the tweed Gibson as we speak :)

[@PrinceWesterburg]

I thought this was a 55min video on tube biasing, watched 10mins then stopped. It stuck in my head though so a few days later I've watched the rest - Wow, what a tressure trove of random elements that together prove its not all maths and music theory, its a whole lifestyle - Please keep adding car meeting sections, hot rods is what kept me playing 30 years ago!

[@UncleDoug]

Thanks so much for your nice comments, Prince. We will :)

[@regortex3364]

tube amps, cats, dogs, hot rods, education, if this was the only channel on KZbin it would be worthwhile.

[@UncleDoug]

Thanks, Reg. We try to cover all the important bases :)

[@jeffreyjhouser]

Fantastic instruction! The Eurotube tester is certainly convenient but I appreciate your snippet of the DIY method, as well!

[@UncleDoug]

Glad you enjoyed the video, Jeff.

[@abelincoln95]

Uncle D- You really are so deserving. You give so much to the community in your depth (or shall I say "girth") of knowledge. I wish I had something to offer. God bless you, Brother... (Edit- You got to love those fighting men that came home from WW II and just jacked up a bunch of cars!! Started a culture..)

[@UncleDoug]

Thanks so much, Abe. Your kind words are reward enough :)

[@eaf27]

I bought one of these eurotubes bias probe devices some time ago and I really like it. I knew I was a bit too ignorant to attempt getting the readings manually, so doing my best to avoid the Dunning Kruger effect and potentially kill myself I spent the money on it and do not regret it. super happy to know that it's proven accurate by one of my favorite uncles! Thank you for sharing your knowledge.

[@amoruzz]

A most professional video. Wonderful generous patrons. That Gibson amp "David" sent is fabulous, not to mention the other items. I've purchased stuff from "Bob" at Eurotubes years ago and always recieved excellent quality and friendly service. Again, thanks for sharing your passion and patience in your videos/tutorials. The car shows are great! Keep your eyes peeled for an old Buick Roadmaster sometime, they have some nifty options on them. I had a few classic cars stolen when I was a younger that I miss. I recently seen an identical one that had been modified from a post into a hardtop and that was a 1950 Plymouth coupe deluxe with visor. The modifications to the body that they did made me wish I still had mine, so I could do the mods too. Absolutely beautiful! Mine was parked by a little old farm lady in 1964 just before she passed over. It had a imitation wood grain dash with a real cool large round clock with a ship on it too. It was stored there and during the Iraq war, metal prices went up and someone snatched it off the property before I could move it. So, who knows what happened to it? I reported it stolen, but the rural county law and state law weren't in the least bit interested in investigating it for some odd reason? Ya win some ya lose some. I believe it had a flat head 6. Pretty nice old car. Thanks!

[@UncleDoug]

Thanks for sharing, Amo.

[@matambale]

You've quite the talent for sharing *great detail* very clearly, Uncle Doug. Plus, there's cats, too.

[@UncleDoug]

Thanks from all of us, M :)

[@bucyruserie1211]

Great demonstration Uncle Doug, of how to use "and build if so desired" the bias probe.. Your gifts from viewers like Jim and others, are out of this world.. I'm expecting some grandmother to send you her Mary Kaye Strat she bought new! You'll have to finish the Corvette story in another video.. Be well, Tom

[@UncleDoug]

Thanks so much, Tom. I greet the mailman every day, hoping for a '59 LP or a nice Tweed Pro amp......but must admit that the latest hauls have been exceptional (as shown in the video) :)

[@Leemuzhko]

The most informative video about biasing. Thank you very much!

[@UncleDoug]

I'm glad to hear it, Alex. Thanks :)

[@tubeDude48]

Very good, Doug.

[@UncleDoug]

Thanks, Ted.

[@jayriver1644]

Classic cars and tube amps. Sounds like a great TV channel.

[@UncleDoug]

Keep watching, Jay. We also feature drone flights, desert excursions, and hot rod rides.

[@brianyork5510]

Thanks to all the gentlemen that generously gave to Uncle Doug, and thanks to you Uncle Doug for another great video.

[@UncleDoug]

You're welcome from all of us, Brian. Thanks !!!

[@sagegc7414]

Thank you so much for this tutorial! I am a novice amp tech and was able to use your manual method to check the bias on my own '78 Hiwatt. Seeing you walk through the entire process step-by-step was extremely helpful.

[@UncleDoug]

Glad it helped, Sage. Best of luck with all your projects :)

[@slickdaddyod3799]

My cat, Souixsie Queue, saw Jack and Casey on the screen, and had to get a closer look. THEN she saw her brand of treats. You've got a new 4 legged fan!!!

[@UncleDoug]

Make sure she subscribes, SD......we need all the help we can get to reach 100K ;)

[@JivRey]

Not saying your old because obviously you're young at heart BUT I wish my uncle was as coooool as you.. Thanks for all that information, a real legacy

[@UncleDoug]

You're quite welcome, JR......and thanks for the nice comments :)

[@Ireland831]

Hi Doug...When I first started building amps, my buddy gave me some home made bias probes for the tube sockets. At some point, they got put in a box and mis-placed. I just started using my meter (an old Simpson 260 my dad gave me). I got fed up looking for my probes, so I finally got some new ones from Eurotubes. I was tempted to get these with the meters, but I felt I would just use my digital meters and save the money (I have an old Radio Shack one and a Fluke 77IV). A few years ago I finally bought an 87V Fluke. Those in your video from Eurotubes look great....easy to use, current and voltage on each tube. Super easy. I keep fighting the urge to get them. Great vid!

[@UncleDoug]

Thanks, Ireland. I agree that the purchase price may seem significant, but after having them for a couple years, I honestly can't imagine life without my Eurotubes bias probes.

[@tonysplace8009]

Thanks David for your generous donation so we can learn more about vintage tube amplifiers from Uncle Doug in future videos!

[@UncleDoug]

Amen, Tony. Thanks !!!

[@cosmoganic]

Excellent, Thanks for the video Uncle Doug & Warm Greetings from the Sunshine Coast, Australia

[@UncleDoug]

You're welcome, Ollie. Likewise from the Sunny Southwest, USA :)

[@daveogarf]

THANK YOU for your generosity, David! More learning ahead. Uncle Doug - This vid was SO informative!

[@UncleDoug]

Actually, the Eurotubes probe was from Joseph V. , Dave, but I agree that David was also far more than generous. I've already begun work on the tweed Gibson.

[@thomasjurgens2590]

Thanks Doug for a new project to build and assist in my amp restorations.

[@UncleDoug]

You're welcome, Thomas :)

[@johnlimbach9267]

Excellent. I have a Compu Bias unit that is similar but has two leads so it will measure two tubes at the same time. Also gives a direct display of Plate Voltage, Plate Current, and Plate Dissipation. Makes bias adjustments a breeze. Pricey, but one of the biggest positives is that it improves safety by eliminating the need to insert your hands in the HV multiple times. If you Google it, you can see some excellent photos of it in action.

[@UncleDoug]

Thanks for your input, John.

[@goodun6081]

At 8:30, the manner in which the multimeter leads are connected between pin 8 of the rectifier and pin 3 of the output tube can also be used to measure actual plate current *directly* by means of the "transformer shunt method", whereby you set the multimeter to measure current in milliamps, change where the probe cables actually plug into the milliamp meter if required ( as it often for invariably is), and turn the amp on. This isn't recommended for the inexperienced or faint of heart, but it will give you a direct in-circuit plate current reading, without any math involved. Just one caveat: most multimeters require you to use a different input jack or even pair of input jacks when measuring current, compared to measuring voltage or resistance, and if you try to use the multimeter to measure current directly but you've forgotten to change which input jacks on the meter you have plugged the test-lead cables into, at best you will blow a fuse on the meter, and at worst you will blow the meter to smithereens! Don't ask me how I know this....😣

[@audiotechlabs4650]

You never fail to amaze! The probe part components are available on several sites on the web. I think building your own probe, like building anything, you know exactly what is in it and, most important, how it works! Like you said, the Euro tester is nice and accurate, but you can build one for under $20. Go figure. If you build it yourself, you can fix it yourself. It's a no-brainer! The cars ARE wonderful! In the early 50s we moved from Mo. to Roswell, N.M.. My dad bought a late model Hudson Wasp. It was, in his words, the best damned car he ever owned and he had many. We moved back to Mo. a few years later to help my Grandfather and the Hudson got repossessed. My Dad never got over it! Oh well. I learned a valuable lesson about over extending yourself. Thank you so much for sharing! Can't wait for the videos on those amps you got in the mail! Love them kitties! Thanxz

[@UncleDoug]

You're welcome, ATL. I have already started on the tweed Gibson GA-2RT and it is turning out to be a great amp......so stay tuned :) Thanks for all your nice comments.

[@billbeyer657]

Another great video. I’ve done lots of business with Eurotubes since they’re local to me. I shared this video with them. Hope you and the cats will be celebrating Cinco de Meow this weekend.

[@UncleDoug]

Thanks, Bill. I hope they are pleased with how well their probe performed. I found it to be a really nice instrument. I didn't realize that such an important cat holiday was upon us......I'll have to go shopping for catnip and play-toys :)

[@renegade44040]

Thanks UD! I learn something every time I see the videos you post. That was some mail call. Thanks David. Thank Jim

[@UncleDoug]

You're welcome, JJ.......and thanks, generous donors.

[@daleburrell6273]

...a real mail call haul(?)

[@drsproc]

I think I'm addicted to these vids. I better go speak to someone. Lol... no seriously excellent to the point technologist makes it look so easy. Luv the concluding segments.

[@UncleDoug]

Thanks, Doc.

[@kenhancock8931]

THANKS UNCLE DOUG hope u have a great day. I saw the cobra then POOF aww man my fav !!!! blue 427 side oilier and white stripes!!! GIMME GIMME GIMME ;-)

[@UncleDoug]

You're welcome, Ken :)

[@matthewf1979]

I just love the cats. Jack must be a union guy on his off day! Uncle Doug, not only are you super helpful tube amp creator, you take care of all the stragglers and homeless bum cats lurking around your yard. Since the strays can’t talk, I’ll say *THANK YOU* for them!

[@UncleDoug]

You (and they) are quite welcome, Matt. We enjoy you all.

[@willievivanco1]

always look at your videos you give a teaching lesson like no other and i thank you for being a part of my educational on electroniics

[@UncleDoug]

You're quite welcome, Wifredo. We appreciate your nice comments.

[@Scorpio722]

Welll done video of the manual bias and the Eurotube Bias Probe.

[@jonathanduffett8374]

Wow! Great video Uncle Doug and thanks to David too. So generous. Amazing!

[@UncleDoug]

Thanks, Jon. Amen on the thanks to Joseph V.

[@jonathanduffett8374]

Uncle Doug Amen indeed! Joseph, Jim and David appreciated. Be a radiator, not a sink!

[@UncleDoug]

Well said, Jon.

[@jeffjeff370]

Today!!!! was the big day!!! first time power on the supro tremverb. perfect!!!! thanks verry much Uncle doug!!!!! used this bias method for the class a 6v6 and it came out on 12.6 watts, but the 6v6s by jj has a max of 14 watts so thats perfect. it will eat a 6v6 tube once a year, but the sound is just amazing!!! also checked temperatures of all components using a infrared temp. meter all seemed verry cool. thank again!!! greetings from holland!!!!

[@UncleDoug]

That's great news, Jeff. Congratulations on the success of your Supro TV build. We hope it gives you many years of enjoyment.

[@jessferrera3155]

Thank you for sharing this information to help us with this hobby

[@UncleDoug]

You're welcome, Jess.

[@snowhyt77]

Thank you for another great vid UD. I'm Glad you were blown away by my donations, They are worth the price of shipping for these master classes in amp restoration. BigDave.

[@UncleDoug]

You're quite welcome, BigDave, and thanks again for your great shipment. I am working steadily on the tweed Gibson GA-2RT and have it working quite well......even the reverb. Next will be the cosmetics. I think/hope you will be pleased with the result.

[@Dennis-mq6or]

I really enjoyed this video. Right about the time I started thinking about what might be inside the Eurotube unit, you started talking about how to make one. Perfect timing! I had pretty much sketched out what you had but was trying to figure out how I could power the meters from the filament voltage so I would not have to use external meter(s) to make the measurements. I would need two fully isolated supplies to power the meters which could easily be done off the filament voltage if it was in the 6vac to 12vac range; but then I hit a dead end when I thought about the much higher filament voltage tubes such as the 50L6......

[@UncleDoug]

The probes won't work with 50L6's, Dennis, only the 6V6, 6L6, etc. family of tubes.

[@AdmiralQuality]

Excellent installment, Doug! This will be the go-to reference for bias measurements on KZbin. I know you've covered this stuff before, but a nice companion piece to this one might be about the decision process that goes into selecting a particular plate dissipation. Would be great to bring up some sine wave test tones on the 'scope and show how they're distorted by the output tubes in different ways under different biases as well.

[@tommyconancoates7097]

I concur. Lol. Uncle Doug is thorough but most importantly very easy to understand.

[@UncleDoug]

Thanks so much, AQ. The determination of PD value has been covered before several times, but the bias to sine wave analysis is a great suggestion. I will keep this in mind for the future.

[@Kettletrigger]

Another great video! When I build mine I think I'll install the tube socket in the junction box.

[@UncleDoug]

Thanks, KT. I can imagine all sorts of neat modifications that would make the test unit better and easier to use. Good luck.

[@jaymichaels5187]

Another super video, Uncle Doug. The Eurotubes device looks like a great buy if one has to bias a lot of amps, as in a repair shop situation. For us who only own several tube amps, the traditional bias method will suffice very nicely.

[@UncleDoug]

Thanks, Jay. I think it will also be useful for those who don't know how to manually check or adjust bias.

[@jaymichaels5187]

@@UncleDoug Yes, you are correct, but I would hazard to guess that anyone who has very little knowledge or is not interested in gaining such knowledge of how to bias their tube amp should pay a pro for that service, as it can save their life in the worse scenario.. or at least save them from causing expensive damage to their tube amp. But as a handy probe to see if your amp is biased correctly or not and take safe corrective action from there.. then it is worth buying it.

[@UncleDoug]

I am not advocating that they also try to adjust the bias themselves, Jay. As I explain in the video, the probe will allow them to monitor their bias and then seek professional assistance when necessary.

[@jaymichaels5187]

@@UncleDoug Right on, Uncle Doug. I get what you are saying. That would be ideal for most amp owners, who want optimum performance but will not work on their amp. Seeking pro help makes the most sense for them.

[@PrinceWesterburg]

I used to work for Audio Note and we all hated the boss' decision to use that Broadway font, used on this unit too. [shudder]

[@UncleDoug]

Sorry you don't like the font, PW.

[@bradincaliphas]

Thanks Uncle Doug, this topic is (currently) out of my pay grade, but I remain teachable. :)

[@UncleDoug]

You're welcome, Brad.

[@bobkins270]

Druel,druel! Old amps old cars. Love the biasing tool! I loved the black Ford. It is very similar to the last one I helped build. More engine than car.

[@UncleDoug]

Thanks, Bob. I agree :)

[@geraldgioia1062]

Best instructional videos on you tube. Thank You

[@UncleDoug]

Wow.....thanks so much, Gerald.

[@alexm1046]

Great! That's exactly what I was looking for, how to make my own tube bias probe

[@UncleDoug]

Good luck with your project, Alex.

[@iangray7410]

I am so impressed by your accountability in learning Uncle Doug. You learned a new understanding of determining plate voltage, confessed to it, and made it the object of this lesson. Talk about metacognitive teaching and modelling! BTW, I am still trying to put together a linear list of your instructional/electronic theory videos, starting from "How a Tube Amp Works" in about 2014 (?). What I chase on this topic is scattered all over KZbin. I have begun a document that lists topics by date of posting but I am so in need of a master list by anyone who has a list of Uncle Doug's "How it Works" videos that starts from the beginning and ends at the most recent. This is stellar learning/teaching and I know it has a logical progression that I can't easily determine. Enough of my beef. I am prepared to send some Bluegrass recordings to the first person who can furnish me with the chronological list of how the amp works from input to output with all the components in between. I warn you: these recordings are my wife's, she being 3x Grammy nominee Claire Lynch. I bet you'll enjoy listening to her music while soldering up and testing your next great build/repair.

[@UncleDoug]

Thanks so much for your very kind words, Ian. I'm quite flattered that you would spend so much time and effort assembling a linear compilation of my video topics. When I first started, I was a novice seeking to share my new learning with others.....thus, the early and very basic "How Amps Work...." series. Then I began to focus on each of the components in the amp, from capacitors to power transformers to vacuum tubes to resistors, etc. pursuing each topic in much greater depth and detail.....with repairs and restorations scattered throughout to break up the didactic tedium and, more importantly, to give hands-on examples of component function and interrelationships and the consequences of their failure. I believe, as a subscriber (I hope), you can access a chronological listing of all my videos. I have not maintained a linear narrative throughout this process, so trying to put it all in logical, searchable order will indeed be a daunting task. I wish you the very best in your attempts to do so.

[@iangray7410]

@@UncleDoug I am a man of my word and would sincerely like to do both things: compile and chronologically order your "How To" videos (as much as KZbin's vagaries allow me access) and also to send you some music from my house. My wife was a back-up singer on three Dolly Parton Bluegrass albums and is a seriously important recording artist in her own right in the tiny Bluegrass world. If you send me a mailing address at [e-mail] I will happily send you a slew of her CDs as a partial thanks for what you are teaching me. Her latest CD is a collection of Canadian songwriters' works played by Claire's own band and supplemented by some of Nashville's finest. Maybe you've heard of Bela Fleck, David Grier, Jerry Douglas, Alison Brown, Stuart Duncan... ? If we can't entice you up to Canada we can sure send you a taste. Oh yeah, that album was also nominated for a Grammy.

[@UncleDoug]

Wow, thanks so much, Ian. My daughter lives in Nashville and she and her husband are cyclists. Apparently, one of their riding pals is a best friend of Bela Fleck.....one of the world's best banjo players. The other names are noted for flat picking, lap steel, banjo, and fiddle. Quite a who's who of bluegrass musicians, including your wife....who is also quite well known and respected. I will contact you by e-mail and would love to receive some CD's. Canada is a "fur piece" from Texas, but good music knows no boundaries :)

[@berniken6511]

Thanks Doug for another excellent informative video.......................................Berni

[@UncleDoug]

You're welcome, Berni :)

[@scottbc31h22]

A tip for building a 'tube interceptor' for octal base, similar to the Eurotubes unit. First, be sure the male plug pins are completely clear of solder. Heat the pin and use a solder sucker to clear the solder. Next, solder a short (2" or so) bare wire (solid wire, or tinned stranded) to each terminal except pin three. Solder a long wire to socket pins 3 and 8. Solder a long wire to pin three of the male plug. The long wires will go to the meters. Now, feed each of the short wires through their corresponding male pin.and out the tip. Trim the wire flush with the tip of each pin. heat the pin and feed solder into the tip of the pin. Use the connectors of your choice to connect to the meters.

[@UncleDoug]

Thanks, Scott.

[@priestblood]

Wow fantastic, i would love a tube tester but way out of my budget in the UK, what a great gift

[@UncleDoug]

I agree, Wayne......very generous.

[@bullthrush]

Very cool little gadget, and fairly easy to copy. Thank you for taking time to show it! The black '34 was impressive, the T-bucket does look odd. Just when you said "tasteful flames", I was thinking "orange kelp". :))

[@UncleDoug]

You're welcome, Andrew. Flames are a polarizing feature :)

[@whatyoumakeofit6635]

Great video Doug. A video that certainly needed to be done.

[@UncleDoug]

Thanks, Bryan.

[@MrsG7swr]

nice instructional video. had a watch last night and the old grey matter dragged up a memory from college regarding DVM accuracy i seem to remember we were told to pretty much ignore the last digit displayed so for 23.33 we would take it as 23.3 and 23.37 would be 23.4 as the meters were not precision instruments. there is probably more to it than that for sure and that was mid 1980's but as I said the grey matter thought about that and your results and thought they would be even closer between the two sets for manual and with that nice piece of kit if taking that view of the meters. but of course it all falls down with the one displaying 263V as there was no decimal to worry about. now to watch the end with the hotrods, what a great mix of viewing pleasure.

[@UncleDoug]

Thanks for your input, Mr. G :)

[@scottroberts3801]

Love the video. Very clear and detailed amp tech info , unbelievably awsome viewer contributions, and sweet hot rods . Don't think it could get any better than that. Oh yeah, and the cat's. My 6 year old son likes to see Jack because he looks just like his black cat named Herman. Thanks for sharing your knowledge and adventures Uncle Doug.

[@UncleDoug]

You're welcome, Scott. Thanks !!!! Regards to Herman :)

[@danielsaturnino5715]

I think I will make one of those. Thanks for the gear donners and to you for making it possible.

[@UncleDoug]

I agree, Daniel. Thanks !!

[@dwightjt]

Pretty amazing the way The mind works once You gain knowledge On things good idea On making your own current probes for electron tube biasing.

[@UncleDoug]

Thanks, Dwight.

[@valakatz3967]

Hello from Canada, Toronto Ontario. Like Always your Videos are educational, Thank you for your efforts.

[@UncleDoug]

You're welcome, V. Likewise from the Sunny Southwest :)

[@jackallen6261]

First I must say thank you, David and Jim!! Any fodder for future videos is awesome!! Next, I have to say these educational vids are my favourites!! Thanks so much for sharing your knowledge with us! Oh and say hi to Jack and the rest of the kitty clan for me!!

[@UncleDoug]

You're quite welcome, Jack. It's always good to hear from you. The kitties are waving back :)

[@69mercurycyclone44]

Awesome build! Love the cars too! I see myself making an amp probe soon. Thank you for all the great ideas.

[@UncleDoug]

You're quite welcome. Good luck.

[@TheBoss1597]

Marvelous Doug! Really a great vid as usual, thnx !

[@46bovine]

Great educational video, thanks Uncle Doug!

[@UncleDoug]

Glad you enjoyed it, Bob :)

[@68macun]

Learn something new every time, Always good stuff

[@UncleDoug]

Thanks, Matthew.

[@Bigjoedo66]

Another great video Uncle Doug! Glad the probe is accurate

[@UncleDoug]

Thanks, Big Joe. So am I :)

[@grassulo]

it's also to RCA being in the great depression and seriously messing up on that radio, I've taken your advice about tube amplifier circuits and Carlson's lab about making it an awesome radio It was an original mess up and bad wire routing which led to an explosion! My cats Ozzy massive panther and Snowy my fluffy girl say hi to you and cat family, and you have taught me how to tune and make a tube amplifier sound awesome!

[@grassulo]

and hot chassis fivers have lower b plus but transformer radios have well yeah...I have used the knowledge you have given me and also Carlson to give old sets high AM band width and tight tuning especially on short wave too, and broadcast AM on them sounds like FM like it should. Don't ever touch B+ on a transformer radio or amp you will get whacked! It probably won't kill you but like my grandpa said it'll kick you like an electric horse! OUCH NO TOUCH! He worked on old school 480v three phase theater lighting...he knew.

[@UncleDoug]

Thanks for all your nice comments, G, and regards to Ozzy & Snowy.

[@grassulo]

@@UncleDoug I think you should name fuzzy girl cat amber and invite her inside!!

[@davidfuller581]

I've always liked Eurotubes. They test their tubes very well, and their bias probes directly measure plate current - which is great because that's considerably more accurate than cathode current, because it removes any screen current from the equation. Also, they're supremely helpful if you email them.

[@UncleDoug]

I agree with all your statements, David. They and their products seem to be of excellent quality.

[@rb032682]

Very nice DIY bias probe.

[@UncleDoug]

Thanks, RB.

[@retrotechandelectronics]

I have their original probe, same probe but plugs right into the multimeter set to mA. I finally got to do a comparison using the ST70 restoration by using the Voltage/mA on the St70 outputs

[@UncleDoug]

Yes, I understand that they sell the probes separately.

[@robertcalkjr.8325]

Nice video and lesson Doug, thanks!!

[@UncleDoug]

You're welcome, Robert.

[@jorgemellooliveira9611]

Ótimo fim de semana para o Sr.obrigado por mostrar esquemas detalhado Sul do Brasil

[@UncleDoug]

De nada, Jorge. Have a great weekend :)

[@jorgemellooliveira9611]

@@UncleDoug thanks my friend

[@johnsimms3957]

Good video! I use my Eurotubes Pro One bias probe to bias my Marshall 2203X 100 watt master volume head. I believe using this probe will pay for itself after about two or three tube changes. Not only that but lifting and carrying this amp to a tech is quite a chore as it's really heavy. The bias probe is worth it in my opinion. I use the probe to keep my tubes out of the danger zone so to speak. I fine tune the bias by playing my amp with the probe installed. I found that I like the tubes to be biased at about 60% dissipation. This gives me more clarity in the bottom end. Which also gives me more crunch without a muddy tone. Another cool thing about the Pro One is it doesn't need batteries.

[@UncleDoug]

All excellent points, John. Thanks !!!

[@matthewf1979]

The EuroTubes bias probe is a nice piece of gear. Not much to it, it’s an Ammeter/DC VM stuffed into a convenient package. Building a multi function dual or quad tester wouldn’t be a difficult task. The parts are cheap enough online. Building an internal power supply is the hardest part. Great haul!! You’re awesome Dave!! 💯👌🍺🍺

[@UncleDoug]

Thanks, Matt. Amen on the thanks to David.

[@maverickdallas1004]

For those who already shelled out a hefty chunk of change for a nice tube amp, the cost of the Eurotubes probe wouldn't be such a bad investment. It's compact enough to store in the back of your amp, and would be a convenient way to keep tabs on your amp's performance.

[@douro20]

There is a guy in Bulgaria who makes a bias probe designed to be used with a multimeter. It has a switch for plate current and plate voltage. It sells for about US$35 on eBay. He also makes custom test adapters.

[@UncleDoug]

Thanks for the input, D20.

[@joeyoungs8426]

Not sure if it’s been mentioned but Tube Depot sells their Bias Scout kit for $20. It’s essentially the socket with two probes that plug into most readers. A bit challenging to assemble but doable. For multiple power tubes I usually set the bias on one and then check the others. Sometimes it requires a bit if back and forth. I suppose you could just get two of the kits and swap probes but I personally wouldn’t. Better yet and safer, two kits and two meters for less than $100 probably.

[@UncleDoug]

Thanks for sharing, Joe.

[@basurofobo]

Amazing as usual! Just a suggestion: you can build a small box for the meter connections and the tube socket.

[@UncleDoug]

Thanks for the tip and nice comment, BF.

[@vhm14u2c]

Always awesome learning experience with your videos, thanks for sharing!

[@UncleDoug]

You're welcome, Vince.

[@markanthony653]

I've never seen this one before Uncle Doug I better pay attention to this.

[@UncleDoug]

Yes, indeed, Mark. It is a very useful device.

[@Mike_HuntizWet]

I use this guy. Love it. It’s great

[@UncleDoug]

Thanks for sharing, Mike.

[@GL64]

Very cool! Thanks for the demonstration.

[@UncleDoug]

You're welcome, GL.

[@abjr2010]

Eurotubes test was very nice. And would come in handy if it was too difficult or very time consuming to get to the test points in the chassis. Good for preliminary test for sure. EEZEE PEEZEE to make. I have to say I've had more fun going old school. Anyway, WOW what goodies you get in the mail. I'm lucky to even get a birthday card. Even Jack and Casey made out. Nice cars again.

[@UncleDoug]

Thanks for all your nice comments, AB.

[@God-CDXX]

i made one of these for $20 ... this was a cool video love the cars

[@UncleDoug]

Thanks, Jamie.

[@waynetoneseekerandersen2213]

I have two of these. Very much worth the money

[@UncleDoug]

Thanks for the positive report, Wayne.

[@pyrotas]

Yet another awesome contribution, sir! Thanks!

[@UncleDoug]

You're welcome, Fabio :)

[@billmiller7138]

Doug, you and I are in general agreement as car critics ;) Great video as always!

[@UncleDoug]

Thanks, Bill. I'm glad someone else shares my views :)

[@gitarlos]

great one Uncle Doug

[@UncleDoug]

Thanks, Carlos.

[@dalerobinson3091]

Excellent video!

[@UncleDoug]

Thanks, Dale.

[@dougroundup7315]

Hey Unkie It's me again- (seems like I recall a Frank Zappa line that started that way???? Ahhhhh Yes I think the Central Scrutinizer) I guess I just have too much time on my hands sitting here in my boxers all day riding out these days of minimal social physical social contact waiting for the coast to be clear of that pesky little virus that is creating so much havoc here in 2020! Spending alot of time online binging on You Tube and working some DX on the ham radio. 15 meters has been opening up a bit too..... Might you be a ham too? Well what do I have to say today that is relevent? Ok, great videos and great karma. This one is no less than great with excellent info and excellence at describing and explaining the processes of measuring bias. I never could understand why someone would go to such great expense as to purchase a tailor made commercial bias measurement device when there is a multitude of ways to measure bias and dissapation for free with your multimeter. Or for that fact it is so simple easy to build your own break out setup as illustrated in your video. I have employed many different techniques. In most scenarios I would usually measure the voltage drop across a cathode resistor and take the plate reading and not worry too much about fudging for the grid. I figured that it would fudge my dissapation calculation just enough to ignore and yet offer a margin of safety above over dissapating my output tubes. I often used to have an ear and a habit for runnin' em hotter anyways... Oh the errrr of my evil ways! When I started doing alot of amps as a service to others instead of just my own , it became more convienent to build a plug in device where I wouldnt always have to remove a chassis. So I built my own break out. Mine a bit different than yours for sure but likely not as accurate because of grid error and maybe not quite as versatile. BUT..... Certainly much SAFER! I employed a 1ohm precision resistor inside of my "Probe" with no high voltage current traveling thru my leads or into my meter. I am scared of high voltages (would you believe I have a specialized tube with a 7000V plate at over 500mA,power supply??? YIKES double digit kW output!) Getting off subject I digress except to say that yeah I am very fearful of high voltage but thats healthy! Long story short, I dont like running flying leads to the tubes and I would also like to add that maybe you might want to re edit the video to include a warning that whatever a potential builder to this device does, is that they clearly make sure that the leads that they use can clearly support higher voltages and that they dont use some innappropriate low voltage signal wire that could potentially break down the dielectric properties of its insulation! I didnt want to be critical but it might be worth pointing out. Back to the commercial bias measurment devices..... I thought I wouldnt ever find value in buying one of these types of devices UNTIL I ended up buying the most expensive, easiest, laziest and probably the safest and accurate one of them all. (this is not a product plug as a matter of fact I think that the maker has since retired and its no longer available or rarely avail. I am not sure?) I have a device called the CompuBias. It is a breakout socket similiar to all the others and it reads the actual current and voltages all very safely at the actual socket with no dangerous currents thru the meter or the leads. It has a microprocessor with its own firmware program (probably a PIC of some sort) and it will read your voltage, current and power all on its own LCD screen. YES for those kids born into the calculator age and slide rule is foreign to them,,,,,, This device performs all the calculations for you and gives you the power being dissipated too. EASY PEASY STUPID SIMPLE but almost stupid expensive too! However, it is such a productivity time saver and I was able to justify it as a start up business expense.... Which also I must comment on your estimate of professional help costing to bias an amp! I KNOW I AM UNUSUALLY CHEAP AS FAR AS WHAT I CHARGE AND I DONT HAVE ANY SET PRICING ON MY SERVICE But DAMN $100 bucks to bias an amp! WOW! Maybe I need to research my marketplace better. I know that I am probably in a more competitive location where amp techs are likely a dime a dozen with all kinds of fly by night hacks that do more damage than good but I just cant look someone in the face charging a hundred bucks while I pull out my little black box and it is so simple! The guy that called with a twin the other day, I only quoted him 20 bucks to check bias on the new tubes he bought and installed. (I know that was lowball and the luthier that I partnered up with on the shop gave me a ration of grief, but I figure it is a good investment in yet more future business,,,, (like as if I need to advertise or get more clientele, I am comfortable with the amount projects that I have to do for others for the next few weeks ) Finally in closing, I also want to thank the genrousity of your viewers and all the goodies that seem to be sent your way! I enjoy watching as you unbox some of these treasures! Especially the thoughtfulness to include goodies to your co-stars . I never been a cat person and now we have three. My snowshoe being my favorite furry child...... Wow! NOS tubes and vintage valvco and other misc..... Glad to see that good karma goes around (as if karma really works like that) and comes around. (Its good karma when I wake up and nothing bad happens and I dont learn a lost lesson the hard way!) Nice guys dont finish last after all! PS: your videos remind me of and look suspiciously like those machine shop videos by "TUBALCAIN" Your undercover is safe with me! GO CHECK HIM OUT!

[@UncleDoug]

Wow, thanks for all the many and varied comments and observations, Doug. We appreciate hearing from you.