Oscilloscope: DC & AC, Signal Tracing in Amp Circuit, RMS Output Measurement

[@UncleDoug]

As a former math teacher, I'm embarrassed to admit that there is an error in my formula for the calculation of RMS power. The peak voltage should be corrected to RMS (i.e. multiplied by .707) prior to being squared and divided by the speaker impedance......not after :(

[@NotMarkKnopfler]

So, about 2.25 watts RMS?

[@harbselectronicslab3551]

Thats fine.....it makes some of us feel smarter lol.....another worthwhile video uncle Doug......I get all the young trainee's to watch these, its very helpful :)

[@UncleDoug]

Yes, Not Mark, the real value is a bit lower than my flattering portrayal of its awesome output power :)

[@UncleDoug]

Thanks, Harb. I always strive to make others feel smarter :):)

[@UncleDoug]

Thanks, Gianfranco. We will :)

[@kenwinston2245]

Knowledgeable men such as yourself who are willing to take the time to share are rare, and absolutely beyond value to the rest of us . Thanks again sir. You will always have a willing and eager audience.

[@UncleDoug]

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

[@aeyb701]

When I came across your channel a few years ago I thought this guy must have been a teacher. Your pedagogical skill comes through. With you I simply get it. Glad you’re out there.

[@UncleDoug]

Thanks so much, AE :) I was a classroom math and science teacher for many years.

[@kennethgroves6552]

Uncle Doug is the teacher that we wish we had in school. Thank you Uncle Doug!

[@UncleDoug]

Thanks so much, Ken :)

[@knifeswitch5973]

Well Doug , I’m a 53 year old electrician who never got into electronics until watching your videos. When this covid thing broke out, I decided it was time for a new hobby. So I bought a bench scope, bench meter, a new solder station, a couple of power supplies, variac and a sig-gen. I’ve been watching your vids pretty religiously and you have taught me so much already. I really have to thank you sir. I doubt you’d ever need it but if you ever have mains or premise wiring issues, I’m all ears!

[@UncleDoug]

It's quite gratifying to hear that you have put the videos to good, practical use, Mike. Congratulations on your new hobby and best of luck with all your projects.

[@franciscoferreira-eh1yu]

I hope you are still doing well. One small tip: if you can buy a book names the art of electronics do it. It will speed up tremendous your learning curve.

[@michaelmasin1996]

I alredy know how to operate an oscilloscope, but I still watch these videos just because I love how you teach

[@UncleDoug]

Thanks, Michael. I am flattered that you would do so :)

[@Cavemannspace]

DITTO! Besides we have to keep an eye open for Jack.

[@gt6hudson]

Like wise, uncle Doug really explains amps so well

[@d.e.c1609]

Same!

[@colvinator1611]

This teaching session was excellent in every respect, in my opinion, Doug. I'll be watching it again to better understand the probe functions. Thanks a lot. Colin ( England )

[@UncleDoug]

Thanks for the nice comments, Colin.

[@jeremiahchamberlin4499]

This is the best oscilloscope tutorial I’ve ever seen. Took me way beyond what I learned (and taught) in Community College.

[@UncleDoug]

That's great to hear, Jeremiah. I'm glad it was helpful.

[@OIE82]

I love Uncle Doug and his videos. Every time I was thinking "but what about..." he answers in the video. God bless Uncle Doug.

[@UncleDoug]

Thanks, Luther.....glad to hear it :)

[@CesarVitell]

I never post a comment all this years, I follow you since the beginning and see all yours videos. Your a true Maestro. i just want to say one thing and i just want to Thank you for all I have learned from you Oncle Doug. Thank You.

[@UncleDoug]

Thanks so much for your kind words, Cesar.

[@EmbelekoBand]

Always appreciative of your shared knowledge. Didn't see Jack's new friend on this video. Miss Rusty very much. RIP

[@UncleDoug]

Thanks so much, Gil. Ollie was being demure during this production :) Yes, I miss Rusty also :(

[@MrBrymstond]

Uncle Doug+ Very professional. I love the fact you go into detail for the beginners. Most would overlook most of what you do, thank you! This is a real seminar, not the average KZbin video.

[@UncleDoug]

You're welcome, Mr. B. I appreciate your nice comments.

[@alanstahl594]

Uncle Doug is a friggin genius !!! I just can't get enough ! These videos are off the hook ! SUPER WOW and many thanx!!!

[@UncleDoug]

Wow......Thanks so much, Alan :)

[@cowasakiElectronics]

Doug. I wish you had been my electronics lecturer! There were so many things that I didn't understand that It took me years to realise. This is probably, no definitely, the best simple introduction to a scope. Again it took me years to work most of this out.

[@UncleDoug]

Thanks so much, Darren. We're glad the video was helpful.

[@horsthartung4682]

Excellent video.....I bought a Sencore SC61 Oscilloscope and a Tenma 72-455A Signal generator like yours and followed everything you said on this video...I'm soon going to be one of your patrons cause I love your videos and the way you teach....I also like Mr Carlson's Lab videos but there soooo long and a lot of stuff he says goes over my head.

[@UncleDoug]

Thanks, Horst. I'm really glad to hear that the videos were helpful. Best of luck with your projects.

[@DennisMurphey]

OUTSTANDING, you range of topics is just awesome. I had a scope and signal generator and sold them because i had no idea how to use them properly. Had i seen this video i would certainly keep them to check these homemade Amps. I had not idea how much fun amps can be. Well I will keep looking for bargains. maybe i can get another set of gear. This was great no part 2, Thank You Doug . You may not appreciate that your videos even older ones are helping a whole of folks figure stuff out. I expect even after we are all gone these video will be watched and education even more people. What a great act to do for education. D

[@UncleDoug]

Thanks so much, Dennis. It's great to know that the videos are helpful.

[@DennisMurphey]

Check your PayPal. Small token of appreciation. Go get an ice cream in your Hot Rod on me. D

[@UncleDoug]

@@DennisMurphey Wow.....thanks again, Dennis. Our best to you and yours.

[@andersf324]

As far as output transformers, when I have instructed fellow musicians in the past on the concept, and they are staring at me like I am an alien with three eyes and green hair, the analogy of an electronic gear box seems to make the light bulbs come on. The conversion from horse power to torque with a gear ratio to climb a steep hill (and the speaker transducer is a mighty steep hill for the poor power tube) does provide a tactile concept for them. Great video as always, Uncle Doug!

[@UncleDoug]

An excellent comparison, Anders, and one to which all automobile enthusiasts can relate. Thanks !!!

[@andersf324]

And, as always, we are bound to the irrefutable laws of thermodynamics for conservation of energy. As one parameter comes up, the other one goes down, but the amount of work is still the same. All other variances are in either friction or flux core heating thermal losses depending on the system... Don't get me started on the free energy cooks... Hehe

[@UncleDoug]

Right you are, Anders :)

[@cepwin]

Thank you Doug! Thanks to your videos I was able to get an old Leader 3100a I bought off ebay up and running. Love your cat...beautiful kitty!

[@UncleDoug]

That's great news, Cep. You're quite welcome :) Jack says, "Thanks".

[@max79444]

Doug, you have an absolute fantastic bed side manner as we say in the UK. !

[@UncleDoug]

Thanks, Bryan......I guess ;)

[@sting1111]

Greetings uncle D! Signal tracing has always been my favorite topic of your videos. Its always good to revisit your award -winning videos. They also offer hi level entertainment and make this subject fun and rewarding when we apply your techniques and solve problems. I want to thank you again.

[@UncleDoug]

You're quite welcome, Mr. K. Thanks for the nice comments :)

[@Spencervs]

Hey Doug, Thank you so much for this video series. I found this very oscilloscope at work and they were throwing it away. Took it home and couldn't work out how to use it at all. I'm very new to electronics and I almost gave it away. Your videos helped me to understand how to use this to take my first measurements where others just left me highly confused. If you have more tips, please do share them! 👏

[@UncleDoug]

I'm glad the video was helpful, Spencer :)

[@brianfletcher9774]

I LOVE your kitties ! Puts a smile on my face when you feature them in your videos. I have a cat myself, his name is Thunder.

[@UncleDoug]

Thanks so much, Brian, from all of us :)

[@willykanos1044]

Thank you, Uncle Doug. I needed this to trace the signal in my Princeton Clone. Now I know how to do it. You are a good teacher. Jim

[@willykanos1044]

Here's what I did: I set the signal generator to make a 1khz signal into a dummy load. Measuring the output of the SG on the oscilloscope I found it was putting out 0.5 volts +/-. The signal passes throught the 12AX7 preamp and the signal at the grid of the 6V6 read just 4V +/-. 4V x .707=2.93. 2.93 x 2.93 = 7.99. 7.99 divided by 8 ohms gives just one watt. That's with amp volume at about 40%. Breakup starts at 5.2 V +/- for 3.38 Watts. I measure the output of the audio transformer at the speaker - same settings - and got 0.6 V +/-. 0.6 V squared is 0.36 which, divided by 8 ohms gives a power at the speaker of 0.045 watts. That explains low audio output. Does it also indicate a bad output transformer?

[@UncleDoug]

The signal from the output transformer at max volume before distortion should be much higher than this, as you already know, Willy. Have you checked the DC resistance of the primary and secondary of the OPT, or attempted to measure its winding ratio ? How about a possible short in the voice coil of the speaker ?

[@willykanos1044]

I will check DC resistance of both sides of OPT and check back.

[@willykanos1044]

DC resistance - primary - common to 5K connection: 494 ohms. Secondary - common to 8 ohm connection 1.3 ohms.

[@willykanos1044]

Resistance across speaker connections: 6.4 ohms.

[@CraftAero]

Re: AC and DC co-existing within the same conductor. I tied my brain into knots trying to follow and interpret tube amp schematics before I caught onto this principle. Finding that simple key removed the "magic" and suddenly there was light. :)) Years later, I think I still have marks from all the head scratching.

[@UncleDoug]

It does seem paradoxical........but truth is often "stranger than fiction" :)

[@daveb9370]

CraftAero Same here. I was reading the tube amp books I have, but nobody came out and said it; it was assumed you knew it. Then one day a few years back I was watching Uncle Doug being coached by Rusty (RIP Rusty, we miss you) on this, and BAM! , there it was! The mystery was solved. Thank you Uncle Doug for your great videos. Love the pet cameos too!

[@daleburrell6273]

...no brains, no headaches(?)

[@stevenjozefik659]

Thanks Doug , This is definitely THE best scope tutorial i have ever seen .

[@UncleDoug]

Wow, thanks so much, Steve :)

[@sting1111]

Fascinating stuff as always. Greetings to Uncle and Jack. You get me back into this every winter.

[@UncleDoug]

Greetings, Sting. Welcome back :)

[@pb7379-j2k]

Fabulously instructive video. KZbin exposes these to me in mysterious order, but I'm glad I finally got to this one! Thank you so much

[@UncleDoug]

It's our pleasure, Paul :)

[@robrobinette]

Great video but I don't recommend leaving a light bulb current limiter hooked up to an amp when signal tracing or measuring output. The limiter will feed the amp a low voltage and all amp voltages and measured gain will be lower than normal. Once you verify an amp is powering up normally go ahead and disconnect the current limiter.

[@UncleDoug]

Thanks for your input, Rob.

[@Valerifon1]

I thoroughly enjoyed this video! It was just what I needed! I have a couple of scopes but my use of them is very basic. Many thanks to Uncle Doug and to the generous subscriber who donated the amplifier utilized in the making of this video. Using an oscilloscope and tracing a signal for grounding errors and failed components are what I need to see the most. I'm glad to have found this channel and this video - thank you very much Uncle Doug! I've subbed your channel and will become a Patron very soon! All the best - Luther

[@UncleDoug]

You're welcome, Luther. Best of luck with your scope education.

[@philipdonovan6510]

Once again, thank you for the clear/informative video's. For Christmas i'm getting a Siglent 4 channel 100 Mhz scope and I just won bids at work (Zoll Medical - Leader sig gen, Fluke DMM and a 10A/20V power supply) so, I'll have a fairly well rounded home lab bench in a few weeks. Having successfully build and gig with 2 tube amps, it will be nice to finally "see" more deeply into what is going on in each gain/transformer stage of subsequent builds, mods, and some day designs. Thank you!

[@UncleDoug]

Congratulations on a fine acquisition, Phil. We hope it serves you well for many years.

[@johnkidd1694]

Fantastic demo. With the adding I understand now how amplification is possible.

[@UncleDoug]

Thanks, John :)

[@utubehound69]

I always used my tongue to test the 9V's. Thanks Uncle Doug for most the enjoyable educational episodes ever caught on video they are Gold. I do appreciate them & you I always learn something. Excellent teaching.

[@UncleDoug]

You're welcome, W4. Thanks !!!

[@joemcgraw5529]

your detail in explaining and using it with therory calculations is very informative ,I learned alot about the ossiloscope and how to adjust it for signal tracing ,thank you so much Doug your a Great teacher!!!

[@UncleDoug]

Thanks so much, Joe.

[@dougtaylor7724]

Amazing amount of information available in one video.

[@UncleDoug]

Glad it was helpful, Doug :)

[@romusromulus]

Uncle Doug,how did I ended up here? I was trying to understand how AC is measured by 10x probes. Usually I'm here for amps, this is a bonus info video.

[@UncleDoug]

I'm glad it was informative, Sahin.

[@PandemoniumMeltDown]

Well that was a lot of fun from a simple circuit in very capable hands :) Everybody makes mistakes, the important part is to notice and gracefully correct them; making you, sir, a gentleman and a scholar.

[@UncleDoug]

Thanks so much, PM :)

[@rciancia]

Doug, this video is very much appreciated. It clearly explains what I thought I knew already. Thank you so much..

[@UncleDoug]

You're welcome, Ron :)

[@icemanplaysguitar]

Thanks Uncle Doug! This series has really helped me to utilise my Tektronix TAS 465 in a safer and more useful way. I was unaware of the potential hazards without the use of an isolation transformer, which will be my next purchase. In my opinion, your videos are the most clear & succinct explanations on these interesting topics available on the net. Looking forward to future episodes! Patreoned!

[@UncleDoug]

You're welcome, Ice. Thanks for your nice comments.

[@carvingbone]

Awesome stuff as always! Yes please more videos about uses and trouble shooting on amps like this! I just scored a similar analog oscilloscope to my tool kit, yay!

[@UncleDoug]

Thanks, CB. We will :)

[@AdmiralQuality]

The clipping point is also dependent on the strength of the input signal. Electric guitars don't output anything near +/- 2V, so that's why it went into clipping at such a low volume as the signal generator is overdriving the input compared to what it was designed for. Another great video, Doug, thanks again!

[@UncleDoug]

That's a good point, AQ. I thought my input signal was +/- 1V, but you may be right about it overdriving the circuit. You're welcome.

[@zaraak323i]

I've always operated under the impression that typical guitar signals are 300mV pk-pk and line-level signals are 1V pk-pk. This is something that I think I picked up from Craig Anderton's book.

[@UncleDoug]

I tested a pair of humbucker pickups several years ago (both activated) and got a 0.7V output. To me, 1V is a close approximation that allows for easy numerical comparison.

[@repairitdontreplaceit]

as always great info for old timers and new tube guys , thank you sir

[@UncleDoug]

You're welcome, R & R :)

[@arthurrae7904]

I appreciate your methodical approach to introducing us to a CRO. I particularly appreciated you saying things like BNC Connector, in a manner which could be understood. I am working with model trains and considering purchasing an Oscilloscope. I am hoping that such a device could record a sequence of events, and allow me to play them back. For example, a Capacitor Discharge Unit (CDU) charges a large value Capacitor (I'm using 10,000uF, 63Volts), by directing a supply voltage of 16VAC through a Non-polar 220uF 50Volt Capacitor, thence splitting the flow to two diodes pointing in opposite polarity, which charge the big capacitor. I wish that I could include the schematic, but you can probably get the idea. After a couple of seconds, the big capacitor is changed to about 44VDC, and is ready to supply that jolt of power to a Solenoid, to change points. I would like to be able to record that couple of seconds, and play it back in slow motion. I am hoping that an Oscilloscope could do that for me. Thank you for an interesting presentation. I hope that you, or one of your subscribers might respond to this entry, Arthur

[@UncleDoug]

I don't own a digital oscilloscope, Arthur, but some models may be able to record and playback. You'll have to check on Ebay or the internet in general. Good luck. Thanks !!

[@larrydering1598]

Fantastic instructions with clear and precise information. I really enjoyed this. Thank you for your lessons.

[@UncleDoug]

You're welcome, Larry. Glad it was helpful.

[@midmodaudio6576]

Thank you for that very detailed explanation and demonstration.

[@UncleDoug]

You're welcome, MMA. Glad you liked it :)

[@achdee55]

Thanks Uncle Doug, you are a great teacher!

[@UncleDoug]

You're welcome, Harold. Thanks !!!

[@HipocratesAG]

Thank you very much uncle Doug. This educational series are awesome.

[@UncleDoug]

You're welcome, Sergio.

[@thomasburnett4712]

Thank you, thank you thank you for all the practical instructional videos!

[@UncleDoug]

You're welcome x 3, Thomas :)

[@KP11520]

Now I know why so many others rave about YOUR videos. Thank you!

[@UncleDoug]

Thanks, KP :)

[@ka9dad]

I have a nice older tektronix 453 but no practical experience. Thanks for a very clear explanation amd demonstration of the basics I needed to see.

[@sidarris]

Outstanding videos. Can't compliment you enough :) You are a legend Doug. All the very best from Ayrshire, Scotland :)

[@UncleDoug]

Wow.....thanks so much, Alf. Likewise on the good wishes :)

[@isoguy.]

Awsome video, again clearly explained, thankyou for sharing

[@UncleDoug]

You're welcome, IG. Thanks !!!

[@GL64]

Yes!!!! That was great. Thank you for doing it! More scope vids please!!!

[@UncleDoug]

You're welcome, GL. They're on the way :)

[@SDsailor7]

I second that!

[@papaw2937]

Thanks for another terrific video, Uncle Doug

[@UncleDoug]

You're welcome, Bryant.

[@simonkormendy849]

I've got two dual-channel Oscilloscopes in my collection of test equipment, one is a solid-state 20Mhz DSE Q-1804 I bought back in the late 90's, the other is an old Telequipment D33R 15Mhz Tube Oscilloscope that needs a new CRT and some restoration work done on it, they really are useful pieces of test equipment to have, once you know how to use them properly, having the ability to see how a circuit is actually behaving is like the difference between working blind and working with 20/20 vision.

[@UncleDoug]

That's a good analogy, Simon. Being able to see wave forms and "noise" eliminates the majority of guesswork involved in electronic repair.

[@PrinceWesterburg]

Thanks every so much for this - I've heard people say you can blow yourself up with oscilloscpes on amps but the same people will tell all sorts of old wives tales about valve amps! Thanks for explaining the sea of controls, fairly simple really. Much obliged Doug!

[@UncleDoug]

It's our pleasure, Prince. Don't let the lunatic fringe (we all know you're out there) interfere with your appreciation of vintage amps and oscilloscopes ;)

[@Earthstein]

Superb Uncle Doug. Thank you. I still miss Rusty.

[@UncleDoug]

Thanks. So do we.

[@edwardtaylor1000]

Great video again looking forward to the amp restore and some more of your guitar playing

[@UncleDoug]

Thanks, Ed. I'm going to let Jack and Ollie perform the sound check duties for the Trusound video :)

[@danielcgomez]

VERY informative video Uncle Doug. since I got my cheap scope on Amazon, I've been signal tracing my amps, and having loads of fun!

[@UncleDoug]

Thanks, Daniel. That's great news. Keep up the good work :)

[@rjprivate]

Thank you for another great lesson uncle Doug. I will have a look if you made more of these scope videos. Never used one but I'm at the point I should. It would be great to see how to find problems in tube amps with it. Jack is an awesome cat, great to see him in your videos. I would sure hire him for amp sniff tests

[@UncleDoug]

You're welcome, RJ. Glad the videos are helpful.

[@brd400]

Thanks uncle Doug I like the way you explained it it makes so much sense and it's very fascinating ... I have a basic understanding of electronics and I completely followed what you said and learned a lot thank you

[@UncleDoug]

You're welcome, Brd. I'm glad the video was easy to follow :)

[@Delatsch]

I used to hate Thursdays, but it's rapidly becoming the best day of the week.

[@UncleDoug]

I generally post videos randomly, the moment I complete them, D; but I guess that Thursdays have been coincidentally picked several times now.

[@Sonikbytes]

love this video and how you put everything together to make it safe for beginners like me when dealing this type of circuits. my request is to show how tube tester works. Have a couple of Ampex 620 laying around that need rebult

[@UncleDoug]

Thanks, SB. The oscilloscope is demanding enough for now :) All tube testers are different, but I guess it might be worth explaining the basic principles upon which they function.

[@stevenjozefik659]

Good Idea , Mine takes the plate voltage from mains potential .. Im in Australia , so I use a 110 volt stepdown tx to isolate , however , if i was in the states , i would be onto Doug's iso ps videos straight away .

[@Guitar5986]

These have been incredibly helpful thank you!

[@UncleDoug]

Glad to hear it, G :)

[@gregpeirce6121]

Hi, thanks for the video, very helpful, from UK.

[@UncleDoug]

You're welcome, Greg :)

[@lacorrida]

Best to teacher ever ,master Doug...

[@UncleDoug]

You are too kind, Mathieu. Thanks !!!

[@abcdefgh-sh6wr]

Simply wonderful explanation, thanks.

[@UncleDoug]

Thanks, Nasir :)

[@elmakednos]

I like old style cro. I have also the same tech.I also love the frequency generator.You made a perfect combination of the limiter and the isolation transformer.I have enjoyed it and learned something usefull.

[@tonyrink9999]

Great video. Learned a lot. Thanks for sharing.

[@UncleDoug]

Glad it was helpful!

[@c_b5060]

I learned something new today. Thanks!

[@UncleDoug]

Glad to hear it, CB :)

[@murfbass]

You're the best Uncle Doug

[@UncleDoug]

Thanks, MB :)

[@daleburrell6273]

...and he really knows his stuff-too...(!)

[@johntempleton6368]

That was a good one. When you overlay the output and input from V1 you can see the amplification and signal inversion. Just like school. I also love to hear the sound of the tubes singing, but never really understood where the vibration to create sound comes from.

[@UncleDoug]

I forgot to mention the phase inversion at each stage of amplification. There is a faint, very high-pitched "whistle" from the circuit, particularly with the volume turned way up.......I always thought I was the only one who heard it :):)

[@skycarl]

Thanks Doug,,, once again excellent video on this subject.

[@UncleDoug]

You're welcome, Carl :)

[@lf-1942]

Excellent video. Great information here. Explained better than what I have found elsewhere. Just curious did this include before and after of all tubes? I am unsure of how many times were in this amp. Schematic may have helped. Thanks again.

[@UncleDoug]

You're welcome, LF. I honestly don't recall. Was the answer not evident in the video ??

[@lf-1942]

@@UncleDoug From my notes, :) it stated +/- 1 volt for the frequency generator. +/- 8 volts for the first stage of amplification and +/- 50 volts for the second stage of amplification. When I looked at the back of the amplifier it appeared to be more than just 2 tubes. One could be a rectifier tube. Also what is the range of amplification for vacuum tubes? Haven't found any info this. Also is there a limit on the number of stages? Is a preamp actually required? These questions also not found anywhere. Ever think of making a video on the different types of amplifiers? It took a lot of studying to find out there are three types(I could be wrong here, just started studying) 1 tubes 2. PNP or NPN and 3 Op Amps. Thanks again.

[@UncleDoug]

Yes, the extra tube was a rectifier. The highest amplification factor I have seen is 100, found in the 12AX7. No limit on the number of stages, but diminishing returns sets in rather quickly. Yes, the pre-amp is required to step the voltage up high enough to drive the output tubes. There are more types of amp, LF. Look up Types A, AB, C, etc.

[@HitchHiker4Freedom]

Another great tutorial Uncle Doug. Jack is a black ninja cat so his skills shine better under the cover of darkness. 😁 Thanks for your time.

[@UncleDoug]

Thanks, CC. Indeed, he is one stealthy guy.

[@davecooper5951]

Great videos Doug. I can now switch on my Tektronix T912 without trepidation ! Incidentally, I'm told my 'scope has a storage function - not sure how to use this yet. Another video perhaps ?

[@UncleDoug]

Thanks, Dave. I'm glad the videos were helpful. The majority of analog scopes, like mine, don't have a storage function, so it's not feasible for me to demonstrate it. Hopefully you can find technical assistance on the internet. Good luck.

[@AnalogOpher]

Amazing tutorial. Amazing teacher.

[@UncleDoug]

You are too kind......Thanks, AO.

[@millstap]

Uncle Doug, quick question. I just acquired my first oscilloscope, a Hitachi V-509. I wanted to check the phase of a sine wave at the speaker terminal. In other words, does the amp circuit produce a sine wave exactly like the input at the output or is it reversed. I wanted to use that info to determine if I should hook my speakers up in reverse. As far I know, a vintage Tweed Bassman 5F6-A circuit inverts the signal at the output. But, I want to check a 1959 Bandmaster. I don't know anything about scopes. I bought it to determine outer foils on capacitors. Not that reversing the speaker leads makes a huge difference in sound, I just wanted to see if it was a doable test. I don't want to use a dummy load, just keep the speakers hooked up. Also, other KZbinrs have me concerned about grounding and damaging the scope. One suggested using a ground lift adapter on the scope plug itself. Thanks for your advice.

[@UncleDoug]

You're welcome, MS. From my experience, the phase of the output sine wave is not a concern. Recall that even at moderate frequencies, i.e. 2000Hz, the phase is reversing 2000 times per second......far faster than your ear can detect.

[@ImTheReal]

Awesome! No more scared about Oscilloscope. Great teacher, really easily to understand. I was wondering here... If you start to talk about space travel using these old amps, probably we'll learn some cool things. XD

[@UncleDoug]

Thanks, Nuno :)

[@JoseVazquez-qu3yd]

Learning one step at a time

[@UncleDoug]

Always the best way :)

[@williamsquires3070]

“10 minutes of theory, and 16 minutes of hands on...” Don’t forget the minute spent looking for Jack! 😻

[@UncleDoug]

Yes, and it was a minute well spent :)

[@CodySorgenfrey1]

Hey Uncle Doug! Love all that you do and can’t stop watching video after video! I’m trying to follow this video to hunt down some noise and calculate my 1965 bassman’s output. I’m having success but one thing I noticed while putting test tone through my amp connected to the dummy load is that I can still hear quite a bit of test tone coming from what appears to be either the power tubes or output transformer! Is this normal or possibly related to one of the many issues that plague this amp currently? Thanks in advance! I always wish I had someone like you looking over my shoulder giving me pointers!

[@UncleDoug]

Thanks, Cody. It's uncommon, but occasionally components in the amp circuit will vibrate sympathetically with a signal input. Tighten the transformer screws and wiggle the 6L6's to see if you can identify the "canary" and maybe stop its duet with the output signal.

[@CodySorgenfrey1]

@@UncleDoug Thanks! It’s very kind of you to take the time to reply. If you’re ever looking for a real challenge this bassman has your name on it.

[@mrkattm]

Another excellent video, you said nothing wrong but I think there may be some confusion regarding DC and AC signals on the scope and the use of the AC DC coupling switch. When the scope channel is set to AC it is capacitively coupled and blocks any DC on the signal, when the switch is set to DC in passes everything DC and AC and will display the AC signal riding on the DC level. Lastly the Add function is purely a mathematical function used to give the addition of the two channels, if is often use to provide a pseudo differential measurements between 2 points in a circuit as apposed to some point and ground. For example to measure the voltage drop across an resistor that is not tied to ground clip channel one probe to one side of the resistor and the channel 2 probe to the other side of the resistor (do not clip the probe's ground clips to anything, actually it is best to remove them from the probes) then set the scope to add channel one and channel 2 and set invert to invert channel 2

[@jkaley]

MK, I'm glad you clarified the AC/DC coupling switch here. It's a major point of confusion for oscilloscope users coming from a multimeter background.

[@DennisMurphey]

Outstanding video finally starting to absorb enough of your lessons. If we don't have a scope how else can we measure the amplitude of the signal from tube to tube. My little 5F1 amp is now stable in heater and HV but no signal at all?? Great stuff Doug, Thank You, Dennis in Virginia

[@UncleDoug]

Thanks, Dennis. Since amplitude is a measure of voltage, you can try to use a voltmeter.....but since the signal amplitude varies constantly, you will never get an accurate reading. The oscilloscope freezes the wave so you can measure its amplitude.

[@repairfreak]

Wonderful Oscilloscope usage tutorial series Uncle Doug. Question: how would you test a tube guitar amp to see if it up to spec on its output power advertised? Do amplifier advertised output wattage always use AC RMS voltage output (converted to watts at specific speaker ohm load) with a 1Khz input at 1V peak to peak on scope? If not, what is the common test input voltage in AC RMS Volts (on a true RMS reading multimeter),or Peak to Peak on a scope at 1Khz used for common testing for determining rated output power? I know with stereo amps line level input can be typically 500mV to 1 or 2V RMS max. Is typical input voltage level at 1Khz for rated power output usually stated in service literature of guitar amps? Would the max output in wattage advertised be specified at pre-clip level, or full pedal to the metal with clipping present? I know I have a lot of questions here, so any assistance to any of my questions would be greatly appreciated. Thank you Uncle Doug, you are a wonderful teacher Sir. 😎👍

[@UncleDoug]

The way amp power ratings are reported varies, so you have to pay attention to the small print to see if the output power is RMS, pre-clip, etc. Naturally, most manufacturers want to make their product look as good as possible, so you have to be careful. I have made a video demonstrating exactly how power ratings are accurately determined. Please watch it :)

[@repairfreak]

Thank you, I will look for this video. Best wishes.

[@UncleDoug]

@@repairfreak Likewise, Mike.

[@repairfreak]

Hello so I see you used 1.0V p/p volts in your test which coverts to .353V or 335 mV. I assume that guitar pickups being of many different designs, can vary the input seen at any amps input wildly. So there is no real hard fast rule of input voltage to use for a max output wattage test to see if the amp is producing to spec output. Since guitar amps are designed purposely to produce desired distortion, and at many different input levels, and at varied amp volume gain and other, power output can’t be solidly designated to spec as in the case with home stereo equipment that has very specific advertised levels for input level at 1khz sine wave with corresponding output level. For home stereo amps are designed to not have distortion & min THD completely unlike guitar amps. Have great week.

[@UncleDoug]

@@repairfreak If you boost the input signal voltage in an attempt to increase the output power, clipping will occur sooner, which will limit any increase in output wattage.

[@jeremywatson3882]

Brilliant! So informative

[@UncleDoug]

Thanks, Jeremy :)

[@JayanthookDass]

Thank you very much for this video, so well explained. I'll definitely wait for your forthcoming videos. Regards!

[@UncleDoug]

You're welcome, Jay. I hope you know, we have already posted over 200 videos for you to watch while waiting for our next new one :)

[@Steve_Just_Steve]

Excellent! Learned a TON! Thank you

[@UncleDoug]

That's good to hear, Steve :)

[@marklange8894]

Excellent video, there is nothing quite as good as a professional teacher, teaching. Side note a 1K tone is industry standard in the RF world mainly because it is close to the center of the AF bandwidth so should not be affected by the audio filtering circuits. It should also make it past most amplifier tone stacks fairly well. Riddle: What is the lowest note that you could possibly play? Answer: a DC flat. I know, ugh.

[@slimh2080]

A long time ago I read some paper from bell labs I think it was that the 1K frequency was derived as a standard for test equipment and experiments because that is the exact frequency of a tuning fork. Also Nice video uncle Doug. Thanks

[@UncleDoug]

Thanks so much, Mark :)

[@tenlittleindians]

Slim Hermer Tuning forks are made in many frequencies. For example I have an old Hammond organ tuner that came with it's own tuning fork. The fork is marked 1318.2 with an E below the number.

[@slimh2080]

Just saying what I read. I assumed it was a fork of a certain frequency of 1k hz and that became the standard. let me try and find the article if it is online and cite it for you.

[@williamdaniels8128]

Enjoyed your teaching active passive termonology also love bld race engines trying to apply this wave form todiesel injector trim scan great teacher

[@UncleDoug]

Thanks, William :)

[@Cavemannspace]

Got a question. Looking at the waveform on the scope @~3:38, the sine wave looks symmetric, +&--. Looking at the trace @~ 23:30 - 23:48, the positive peaks look broader yet not like the input signal @3:38, and the negative peaks looks sharper, more pointed than the top of the positive peaks. Appears to be distorted. Why? You and Jack are like Kato and Inspector Clouseau, you never know where Jack is going to hide or how he is going to attack!

[@UncleDoug]

When approaching distortion levels, the sine wave is altered in shape. The sine wave at 3:38 is undistorted, while the later one is becoming distorted. I have no fancy explanation for this other than what is visibly evident on the screen.

[@markrhine5809]

Dear Uncle Doug, another excellent video, when these signals are mixed, is this the same concept of an AC signal riding on top of a DC signal. In other words, an AC signal being input to an amplifier where there is a bias placed on the amplifier. Thank you kindly...

[@UncleDoug]

Thanks, Mark. Yes, the AC waves ride atop the smooth DC, but never mix......just, as you said, like the AC music signal coexisting with the -DC bias voltage on the grid.

[@jimmccanna]

Hi, I too miss your puppy. Question: I am learning to use my OScope and want to use it to diagnose a problematic SS preamp - a Solo 110. What I am confused about (among many other things) is whether I need to put a load on the preamp (output). If so, do I connect it to an amplifier? Then, the amplifier to a dummy load which I have?

[@UncleDoug]

So do I, James. I am no expert with SS gear, but to me, if you want to observe the performance of a preamp, it should be connected to a power amp and functioning as it does normally, which would also require a dummy load for the power amp.

[@jimmccanna]

Thanks for the reply. I learned from a SS electronics expert friend that a dummy load was not necessary - which does not make much sense to me. But, who am I to question right? Thanks for this video and all the others.

[@lizzielecates4430]

Why is there more "clipping" at the top of the wave form? Around 17:00 in video?

[@UncleDoug]

I don't know, Lizzie, but it's not unusual to see this.

[@robertphelps41]

Lo'der UD ! I smell an Honorary Diploma in "Ampology" coming soon ! Your dulcet tones and ageless wit and humor continue to both impress and educate. I'm only hoping you'll give my Vox clone design a look when it's ready and help me source the difficult bits like Diodes from Mullard for full wave bridge rectification. But in the mean time I will share with my friends and enjoy and wait for the video delights yet to appear. Robert aka jj Thanks ever so......

[@UncleDoug]

I can tell that you're an honor graduate in the making, Robert. You're welcome. Thanks for watching :)

[@TheOpenAirGarage]

Another great video. Thanks for sharing this with us.

[@UncleDoug]

You're welcome, T.

[@johnkidd1694]

"It's not easy for a black cat to hide in a white sink." Sounds like some ancient piece of wisdom. On an unrelated note: I really appreciate your videos. I have learned a great deal. I am developing my own audio electronics bench for working on tube amplifiers and later I will work on ham radio rigs. I have a nice oscilloscope but I do not have a signal generator. I see them varying in price from $15 to $5000. Do you have any advice as to what features I should be looking for? Thank you. John

[@tedpinkerton9411]

Uncle Doug, Love all of your work, I'm slightly confused on the final Peak volt output of 6V DC. Shouldn't that be AC? I thought all current in a sign wave was AC. Thanks

[@UncleDoug]

I'm not sure where the "6V DC" statement was made in the video, but yes, all sinusoidal wave forms are considered AC.

[@tedpinkerton9411]

@@UncleDoug @ ~ 27:16, it is written on paper, "Peak V= 6VDC"

[@jma8352]

Thank you for the great education, now if you will explain hendrix feedback with the strat up agenst the marshal stack extortion

[@UncleDoug]

It's magic ;)

[@LestonDr]

Thank you... would the signal tracing for a radio RF be the same procedure from the antenna?

[@UncleDoug]

Heck if I know, LD. Maybe another viewer will be able to answer your question. I'm strictly a vintage tube amp guy.

[@Cavemannspace]

LestonDr; Yes, could very well and I have done just that as do many, many repair techs. Of course, when you get to the converter and IF stages you will be on a different frequency than the incoming signal, like 455KHz for AM or 10.7MHz FM. Most scopes can "see" those frequencies if they have the bandwidth like Uncle Doug's is 40MHz. 10 to 20MHz will probably work OK too but more bandwidth is usually always better and more expensive, new or used, but just for broadcast bands not that necessary. Also, the very low signal level of regular radio programing may be a little low for some scopes. Of course, if tuned to a station, the signal may be out of the bandwidth of the scope. If you're going to use a radio station broadcast try using a station at the lower end of the band to start with. You'll want to use your 10x probe so it won't load the circuit especially if the radio is solid state, but you may be tempted to your a 1x probe on the first RF amp or at the converter due to low signal level or pushing the bandwidth limits of your scope. That may load the circuit and cause a little confusion about the signal strength. You may not want to connect the RF generator directly to the radio. You can couple it to the radio by using a simple coil of wire to induce the signal to the antenna input, or use a capacitor. By varying the output level of an RF generator connected to your antenna input, The signal level can adjusted so you can get a decent waveform on the scope. And, of course, you can modulate the RF from the generator with an audio generator (many RFGs have a 400 or 1,000 Hz audio oscillator built in for that purpose) so you can see a modulated envelope in the RF and IF stages. So yes, you can use the same technique as Uncle Doug shows here, comparing input and output to look for distortion or loss of amplification, any differences, etc. Just one more thing, since I have time to type. If you inject a known signal into the front end, and have a dummy load connected instead of a speaker (Always a good thing! Don't drive yourself and anyone else in the house nuts.) start with the scope probe in the middle of the signal path. If you see distortion, low or no signal, go half way towards the RF input from where you started probing, maybe output of the converter. ~OR~ if you see good, clean signal, head towards the dummy load, perhaps halving the distance again, like the output of the detector or middle of the audio amp. This will help to quickly isolate where the trouble is, considering the power supply is fine. Check the PS first! Always! Just like Uncle Doug shows. Don't listen to Jack. There are other You Tube videos on this somewhere, maybe not quite like Uncle Doug's, though. Mr. Carlson's Lab, Radio Mechanic, the Radio Shop may be places to try if you're not already scribed up with them. They're very good, too. Hope that helps a little.

[@mrkattm]

LestonDr as Cavemannspace said, you can, but don't expect to see a whole lot right off the antenna because the RF signals will be very small (most will be too small to see on an oscilloscope) and all them will be present at the same time so it will look like noise. If you pass the antenna through a narrow band pass filter you might be able to see the stronger signals but you will start seeing things after your first IF stage, just be sure to keep your probe on 10x because you don't want to load down the signal path.

[@daleburrell6273]

...an oscilloscope probably isn't sensitive enough to detect signals in the microvolt range- that's what you are dealing with.

[@johnwrench4speed]

Thanks for the video. They are very informative and enjoyable. I am very familiar with the use and application of multi-channel DSOs (e.g., Snap On: Vantage, Vantage Pro, Modis, and Verus; and PicoScope) in connection with automotive diagnostics (injectors, ignition coils, fuel pumps, cam/crank sensors, in cylinder pressure diagnosis, et al.). The Snap On offerings evolved to be very good. However, the industry standard, in my opinion, has become the PicoScope because of its many capabilities. It is my understanding PicoScope makes a full line of DSOs. I don't know if these would be suitable for tube amplifier diagnostics, i.e., overkill, but having experience with their automotive version, it seems they would be a very useful tool. Cheers.

[@UncleDoug]

Thanks for the interesting input, JW. I have no familiarity with PicoScope but I'm sure there are sites and videos that do. Best of luck.