'69 Princeton Reverb.....Badly Burned, Brutally Botched, and (finally) Reborn 

Hi Uncle - right on regarding video & audio

Another fine video - do you celebrate Pancake Day (Shrove Tuesday) in US?

Thanks guys. No, we only celebrate Catnip Day......every day :)

I just discovered your videos a couple months

ago and am amazed with your deep erudition regarding electronics. Were you once a college professor or teacher in this field? I’ve learned so much so easily that I had always wondered about watching your videos...

Thanks for your comments, Bob. I hope you enjoyed the video. The PR is now one of the best sounding ones I have ever heard. We can talk about the Bandmaster. Hopefully, it hasn't been worked on previously. Also, the replica cabinet you constructed is truly outstanding. You have done us all a great favor by saving this badly damaged PR from the landfill.

High praise indeed, Edward. Thanks !!

We are all wishing you the very best for a successful treatment and full recovery, Tim. The world needs all the tube amp lovers it can get. Your presence is definitely required.....so get well quick !!!

Good Luck, Mate. 👍

We wanna see you back here in shape soon !!........Regards!...........Lou from Canada !!

Tim, get well soon man. You have folks pulling for you, whether you know it or not. Hoping for the best! Take care, and the very best of luck to you and yours.

Praying for you!!!

It sums up some serious shortcomings in the circuit :)

@@UncleDoug -- serious circuit silliness.

Amen, Ben :)

Well done sir, well done.

@@UncleDoug , Snappy soldering, savvy skills, scientific study, and steely resolve surely solve somebody else's stupid snafus.

Thanks, DF. Fortunately, I didn't get mixed up and play the axe while chopping with the guitar :)

@@UncleDoug Uncle doug I need app doctor I've been using amp for music on my phone during family functions and she started to smell smoky what do I do help Uncle duggy

I saw Uncle Doug at the ER the same day he had his finger repaired. In my case it was an index finger nail was charred by a 6v6... We both sat in the corner wearing dunce caps.

.......and their reward will be a colonoscopy with the unbiased 6V6 that blistered my finger :)

@@UncleDoug ha! they deserve it. Hope that heals up quick. thank you for the great content as always!

@@UncleDoug Ouch

LOL!

@@UncleDoug _However..._ You _did_ notice the cherry-red plates, didn't you? Shouldn't that have given you a clue as to the temp of the tubes? I share you dissatisfaction with the "tech" who did the original work... He either didn't check his work for function, or just didn't give a s**t. I made some wiring errors in my time, but I would **_*never_* have let an amp in that condition leave my workbench.

Thanks so much, John. Yes, excessive mismatch can result in reduced hum cancellation and core saturation......so it must be kept within reasonable limits.

I have been doing this as well for years. We are talking about making music. Not reproducing it...!!

I haven't tried mismatched output tubes but Doug's theory about them makes perfect sense to me.

This is a well known effect in electronic music (pulse width variation) if the upper going, wave is related to the bottom going wave by 3/4 or 4/3 it adds some pleasing even harmonics, though I'd rather be in control. of that by my playing style, picking closer the the bridge or the neck.

Thanks, OR. I changed to a broadband Internet provider (120Mb/sec) and now the videos take 20 minutes to upload instead of 4 hours. I think the slow upload was degrading them.

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

Thats what i do...Ijust keep watching it and watching it and all of a sudden i get a moment of clarity .

@@soulvaccination8679 Same here!

Thanks, Brad :)

The Guitologist I could not agree more.

Matched tubes might have eliminated that very small bit hum that was left in the amp because the hum would have been cancelled in the output transformer The only way to know for sure is to ground the input to the phase inverter. One other possible solution would have been to add a 100 ohm potentiometer between the two 100 ohm 'phantom ground' resistors with it's wiper attached to ground. Then adjusting that pot might be able to 'null out' the remaining hum.

Thanks. No you don't, CD. In fact several of the neighbors have restraining orders against my donning such attire :)

I agree, TM. In this case the previous work is condemnation enough :) Thanks !!!

Thanks, Nick. Be sure to watch my latest video on the Gibson ga55v cabinet :)

You're welcome, Prince :)

You're welcome, Ken. The next time Sergio is over to visit with Jack & Ollie, I'll suggest it to him :)

Don't like to but in...but let's give credit where it's due. Ennio Morricone is Sergio Leone's composer.

A modern Sergio Leone movie will be titled *Twice* Upon a Time in the West. The music will be by Eno Morracowbell.....

@@goodun6081 He has a fever! And the only cure is Morracowbell.

It seems like the wiring of this amp was done by Sergio Aragonês!

Thanks, Tom.

I'm glad too, Murrat......and a little surprised that it wasn't :)

So it seems, Paul :)

My father was a ham radio operator. He built his own radios. I came home one day he was sitting in his chair with a spaced-out look on his face. He grabbed the wrong thing. Electricity went through his hand and blew a 2 inch hole in his leg. The doctor said it could have went to his member. LOL

Thank God he wasn't sitting on a metal stool, GO.

The only thing that happened from it was he was mellow for a couple weeks.

@@guitarocd9984 I guess a shock once in a while is good for the soul :)

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

@@UncleDoug I've just thoroughly enjoyed watching this vid and subbed. Yes I came across this type of thing many many years ago where there was a say 220 ohm pot across the filament winding with the wiper to earth marked as a.... Humdinger !!!! which I believe was in an old reel to reel....

Thanks so much, OL :)

Thanks, Tim. The learning process is definitely cumulative :)

Thanks, Ben. Good advice :)

Those were the days, UB. I remember the big tube tester at the local Gunning Casteel (drug store) where you could test your tubes and buy new ones for 50 cents apiece.

@@UncleDoug My dad Ray had one at his stores, Colony Drugs and before that Orange Hill both in St. Pete Fla. My love for his love of this stuff brought me here.

I remember tube testers in the 5&10 stores and Ace hardware .

Darn right, MR. Time for Jack to "Hang 8".......dew claws don't count.

It was a real challenge, Dale. Thanks.

Thanks so much, Glenn.

Yes, Jack was kind enough to send me the Alamo Futura and reverb tank shown in the video. It is indeed a small world.

Uncle Doug I can make it even smaller, or at least more coincidental. I, too, live in Oklahoma and my son is named “Jack Allen O’Neil” Almost spooky.

Thanks for your kind words and helpful input, Blair.

Thank you, Bruce.

Thanks for the suggestion, Chris. I have posted several video series that show all the steps in building an amp at home......strictly all-tube and point-to-point wiring.

Doug how tough would it be to modify a standard tremolo ( Ive got a 65 princeton reissue) or build a seperate pedal for the early 60's harmonic tremolo? I think the Lads at That Pedal Show with blues player Joey Landreth started a trend last year when they featured Joey and his vintage amps as a half a dozen new pedals with harmonic tremolo have come out.

If by Harmonic Tremolo, you mean the Fender circuit used in amps like the Brownface Concert, it would be a somewhat challenging multi-tube build. I would recommend that you watch my video on building a Rick-Tone Tremo-Boost. It's a relatively easy build with an inexpensive power supply and great tube tremolo effect.

@@UncleDoug "Harmonic Tremolo" is the part that's fascinating me U.D. The amp in question was a brown 1960 Super. Supro makes a pedal that approximates it ($250-$300) I'm at the beginner stage probably not a beginner project. FTR I've watched most of, if not all of your episodes ;0) long story short, I'm a 60 yr old retired/disabled Phx cop somehow Andertons music UK showed up in my YT feed 3 years ago and I got hooked on their guitar paradiso episodes which lead to following Mick Taylor to That Pedal show which lead to you and D-Labs when I started investigating tube amps after taking the guitar back up (starting as therapy for my hands after spinal cord injuries) after a 35 year hiatus.

The really tough challenges are often the best learning experiences, Shy. Thanks !!

You're welcome, Robert :) Thanks !!

I'm with you, Bill. The reason choirs sound so good is that everyone has a different voice.....and the blend is both complex and rich.

@@UncleDoug Brilliant analogy, and we too love your videos!

If it had been allowed to remain "on" for very long, I think the unbiased 6V6 would have probably incinerated the entire block. Actually, I think it was a house fire and the amp, which was in good shape at the time, was a victim......not a cause.

Like uncle doug sez if the amp looks altered keep the fire extinquisher handy and the fire department on speed dial.

@@UncleDoug , I personally know of several cases where solid state, transistorized audio amplifiers or Hi-Fi stereos that were DC coupled and that did not have output relays, or even fuses, between the amplifier and the speakers, actually failed sufficiently to send full B+ ( anywhere from 35 volts to 150 volts, depending on the amplifier) through to the speakers and caused them to catch fire. Whenever we fix an amplifier like this at the stereo repair shop I work for, we add fuses inside the amp or supply appropriately-sized fuses and fuse holders and instruct the customer how to add them into the system between the speakers and the amplifier. The danger is if the stereo is left on while someone is away from home, or at night when everyone is sleeping, you risk Burning Down the House and maybe the occupants with it. Fortunately, most modern amplifiers , at least those used in a home audio situation, will have time delay relays that not only let the amplifier stabilize for a couple of seconds before turning on the output to the speakers, but that also disconnect the speaker wires from the amplifier internally if they sense a significant fault, any DC voltage that would cause speaker damage or worse. It bears mentioning that many high power PA amplifiers do not have relays and might not have speaker protection fuses either. A tube guitar amp, by comparison, is unlikely to set the speaker on fire, unless the output Transformer short circuits, however A Fault In The Amplifier can easily burn resistors and capacitors, then the wiring and the cabinet catches fire. or the tubes get so hot from lack of negative bias that they become cherry red glowing radiant heaters and set the cabinet and speaker on fire.

Nice quotation, Paul......and never more accurate than in today's society.

Thanks for your supportive input, TT.

Hoo !

I know nothing about circuitry in amps. but was your statement based in science. Or just what you hear.

I'm glad to hear that I am not alone in this discovery. Let's hope people become more aware of the benefits of mismatching :)

@@guitarocd9984 Both. I have seen harmonic spectral analysis from perfectly matched vs mismatched output tubes. The spectrum is more complex for the mismatched......primarily even-order harmonics. To my ear, mismatched yields fuller, more musical output. The bottom line, however, is how it sounds to you. Do your own experimentation and see what you think.

Okay I only commented because this was a new one on me. Good to know I'll definitely try it. My dad used to laugh at me when I used to tell him there is a difference in tubes. He was old school. He was dealing with televisions and Ham radios not guitar amplifiers. He's passed on but I never could convince him.

@@guitarocd9984 Don't be afraid to experiment with speakers either. Try a ceramic and an Alnico in the same 2 x 12 enclosure. You'll be surprised by how great they sound together.

You're welcome, Thomas.

You're welcome, Russell. I'm glad the videos were helpful.

Wayne Elliott I’d love to know the answer too...

You have to look this one up. Fender Silver-face Princeton Reverb amps with code A21500 to A25500 were built in 1969. I have a little cheat sheet but there are tons of web sites that list the Fender number scheme.

Thanks, Buddy. You are right on the money :) Since the serial number was close to 21500, you can assume it was made early in the year's run.

@@budandbean1 Thanks guys; I had looked at this page superficially: www.superiormusic.com/page195.htm ... and saw "S" relating to 1969, but ... if one goes further down on the page on the right, the TRUTH will be found!

@Wayne Elliott You know, if I had read that page, written like it is, I’d be a bit confused too. 😉

I'll let the owner know, Bill.

@@UncleDoug Yup $24.60 SKU # 9131521

@@Starcrunch72 I ordered a back plate yesterday for the amp.

Thanks so much, SS. We really appreciate it :)

You're welcome, Joseph. Thanks so much :)

Hopefully, the owner will follow through with either Mojotone or your source, C7, to obtain a replacement rear panel. Yes, indeed, we specialize in blasphemy......indeed, we revel in it :)

He seems to be, JP. Thanks !!!

Thanks, Monte. We're glad the video was informative.

Thanks so much, Jason. We appreciate it :)

You're welcome, F1.

Thanks, SW :)

Thanks, Arthur. Agreed :)

Thanks, Austin :)

Glad to hear it, Andrew. Thanks for watching :)

That's great to hear, Andy. Best of luck with your project.

Thanks, Kevin :)

If by "blow" you mean exceed all expectations, then I'm down with that, K :)

Thanks so much, Mark. I'm actually working on my second million dollars......I gave up on the first one :)

Thanks, TM. We will :)

So far the response to my "shocking" assertion has been 100% positive, Stephen.....thank heavens. It really is blasphemous.....but true :) Thanks so much !!

Thanks, David. It's time that more people became aware of this.

You're welcome, Michael :)

Oh, and not to bother you, but I think you might enjoy this podcast. It's called "The truth about vintage amps." www.fretboardjournal.com/podcasts/the-truth-about-tube-amps-ep.-1/

Thanks for the link, Michael. I will check it out when I get some free time.

Thanks for your kind words, HV. We appreciate your comments and input.

You're welcome, Jeremy. We won't :)

You're welcome, Doog. Thanks !!!

Thanks so much, Rodney. Sorry, but the Alamo Futura, being a hybrid circuit, got passed on to another hobbyist.

Thanks, PC :)

You're welcome, Lynn. Thanks for all your nice comments.

I arrived late on the electronics scene and am entirely self-taught, WD. If I can do it, you can too.

Thanks so much, James :)

Thanks so much, Jake.

Thanks, Larry :)

It's our pleasure, HA. Thanks for watching.

You're welcome, David. Thanks !!

You're welcome, Albert.

You're welcome, Hack. It's great that you are able to spot small details like that. Sometimes when looking at the entire circuit, the small stuff is hard to quickly detect.

I'd be lost without them, Dave :)

Thanks, John. So do we :)

Wow, thanks, Michael :)

That's great to hear, Tim. We're glad the videos have been helpful. You're welcome. Keep learning :)

It was a very interesting story, SB. Thanks so much for sharing it with us.

You're welcome, 1967. Thanks !!

Thanks so much, Nelson. Likewise :)

Thanks, Ima :)

Thanks, Seth. I'm glad it all made sense. We do love our Kool Whip :)

Thanks, Karl. Get to work on that Crate amp.....if you don't fix it, who will ? :)

@@UncleDoug So true... I don't have staff here to call upon, hehehe. After I replace melted parts & find no love, what should I do?? I haven't found much for scheme's on this amp....

Thanks so much, Rob. Welcome to our channel.

Thanks so much, Vinny :)