yeah. 25uf @ 25vdc. thats actually what was in the earlier topographies. i believe it corresponds to the Tremolo oscillator. you'll be fine.

@@drew945101 thank you! life saver!!

I bet if he asked "Hakko" they would gift him a good USA made iron.

Question, sir. When testing plate voltage, should I place negative lead to chasse, or to cathode? Uncle Doug uses the cathode, but i've seen others recommend neg to gnd. Larger readings occur with chasse reading. Thanks!

@@jaysorensenIBEW plate voltage is measured to ground -- there will still be voltage on the cathode (before resistor and cap) which would explain the difference you're measuring

@@zjokka Thanks for the reply. Cheers

If it's safe and not going to hurt anyone okay but if not well done for spotting. The aml does sound good though.

Probably the preamp tube. Tap on it with a pencil and see if it's reactive to that. If so, replace.

@@drew945101, thank you.

Because it's turned up really loud. Lol

Most AB165 are black face, but most if not all 68 AB165 are silverface. Some late 68s and early 69 are mislabled with AB165 label, but have a AC568 curciut inside.

Yes. Green wire goes to ground White goes directly to one of the legs of the transformer primary wires (it doesn't matter which one) Black goes to fuse, then to power switch then to the other leg of the transformer primary. Hope this helps.

@@drew945101 you’re the MAN I appreciate all your contributions to this weird and diverse tube amp community….. your directions really helped me.

AA1069 super. www.thevintagesound.com/ffg/schem/super_reverb_aa1069_schem.gif

Wouldn't have been super critical. A 25uf would have worked just fine. Infact, all of the blackface circuits had a 25uf in that spot.

They used to be made here in Lubbock TX. Texas Instruments is an interesting company. Not only do they make calculators, but I've heard that they hold the patent on the technology in javelin missiles. 🤯

That calculator is older than the amp.

Where are you located?

Texas instrument calculators used to be made in Lubbock Texas. That's about 25 miles away from me.

Not in frame, but I have an identical calculator that belong to my grandfather. He was a math teacher in Lorenzo Texas. He was the first teacher there to get a handheld battery operated calculator. Circa 1971

25uf @ 50v

25uf is sort of the standard value you see on cathode bypass capacitors. I've seen 30uf and 50uf used, but in my experience, anything over 25uf is in the realm of diminishing returns when it comes to gain added. 25v on preamp tubes, and 50v on output tubes (only appropriate on cathode biased output circuits, not grid biased). But to be honest, you can probably do 25v caps on single ended output sections like this one here. It was certainly done in the past.

Not to ramble, but once had a guy bring in a boutique amp that had a switch that changed the value of the bypass cap on the first preamp tube from 25uf up to 50uf. The tonal difference was so subtle that he and I both though the feature was broken. Lol! I ended up modding it to go from 25uf to defeated out of circuit (what the blues Jr. "Fat" switch does) and it was way more useful IMO.

@@drew945101 what you said about the tube screamer reminded me of how the silverface champ jumped in value after Joe bonamassa was video'd using one

@@jasondorsey7110 yeah. People are weird.

So that bypass cap corresponds to the triode that drives the optocoupler bulb. It's yet another subtle change in the circuit that actually happened with a later revision of the silver face. Because it doesn't correspond to anything within the signal path; I imagine whatever difference it makes is likely very subtle. My bet is that it limits the peak brightness of the neon bulb and perhaps optimizes the tremolo circuit as a whole, but it would be very interesting to swap it out with a 25uf and hear the difference. The 5uf appears on the AA1069 schematic and forward.

@@drew945101 Sorry, I was wrongly assuming it was the AB763. Mine is a 69 SR with the AB763 which I am in the midst of doing some maintenance on and the 25uf there was fresh in my mind.

@@jimlabos easy mistake to make, the differences are often subtle. Happens to me more often than I care to admit. Lol The differences can be so subtle that I often complete a servicing an amp with the "wrong" schematic and never even notice.

@@drew945101 The 5uF allows the tremolo speed control to track the adjustment of the pot more accurately. With old blackface amps that used 25uF in that position you would experience a delay in the term speed as you adjusted the pot. The 5uF fixes that and has no impact on tone whatsoever. Well done on the video by the way.

@@stevelark9840 well, there you go. Thanks for the information!

Agreed on the bypass cap on V1. I filmed a portion where I AB'd with and without on just the preamp bypass cap, but the footage got corrupted. The bypass on the output tube however made a huge sonic difference and made it much more useful at lower volumes.

Thank you!

I would have ripped out all the dated caps. Replacing them with new caps is best. It’s the circuit not the vintage out of spec caps. Old caps hold back good tone.

@@lestelie4410 I only notice a sound difference if the original cap has drifted. IMHO vintage amps sound great because of the circuit design, not mojo from mustard caps. They sound tired 40 years later and come to life with new caps. Sadly they don't look as cool but if you gig, you want your amp to be 100% and not rely on out of date caps and especially drifted carbon composite resistors. I yank those on sight too. LOL I appreciate your comment.

@@IronandWire Each to their own, I guess. I just wonder if you hearing "comes to life" as the sound of what is now almost a different amp. If you make a cake with the same recipe (circuit design) but use strawberries instead of chocolate (the components) you won't end up with a chocolate cake. But, if you like the sound of your updated amp, that's all that matters in the end. I enjoyed our chat and differing views.

@@lestelie4410 What a weird analogy. Strawberry cake will taste the same whether the strawberries are from Canada or England. Adding chocolate would be a mod. Wink

Thanks for the input!

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