The Amp Garage

solderhead wrote: ↑Tue Feb 25, 2025 4:41 pm
HEY! You gotta remove that JBL tag and replace it with an EV tag!

It’s like seeing a 340 Duster, but it actually has a Hemi in it.

Smitty wrote: ↑Mon Feb 24, 2025 3:25 pm But changing out the white Mallorys? Wow! Instant tone upgrade.

How would you describe the tone change?

I have a 1971 SuperSix reverb that is 99% original (other than the bias and power supply caps), and it is a great sounding amp, white Mallory’s and all.

Since were doing show and tell, here’s my ‘68… These were factory recones from the early 90s (Mark IV industries) that sat unused in their shipping boxes until last year.

Maybe a good reason to get an ultra linear silverface Twin Reverb….with JBLs…Tele with 1M volume pot, and out of tune strings. Play my version of Van Halen I with a long chord set up in the shed. Or maybe a wireless, and a webcam set up underneath so I know when to bang out some noise.

Looking to dyi a relatively cheap but powerful >20KHz tone setup to mount under the floor of my shed in the backyard. Something like 1000W, or more. Bonus if I can generate 2 dissonant sweep tones on demand.

No schematic available yet?

My feedback resistor was too high, >1.2k, so over 40% high. The tail-ground resistor was in spec at 104. Quite an enlightening experiment…a parallel 1k to the now 1.2k (550) gave it a Twin Reverb like tightness. Paralleled a 3.3k for now to get it closer to spec while I await a replacement resistor....

I think linear is stock, but audio taper may give you better control of the lower part of the reverb ( never tried it myself).

I prefer 470 for fenders, but if you will be cranking it a lot and/or with pedals, 1k might work better.

The other experiment I want to try is plugging the amp into my QR speakers. In theory they are the same oxfords, other than the Swiss cheese basket and 16ohm impedance, but the QR sounds great with them.

He doesn't have an AB165 Bassman. He has an AA165 Pro Reverb. [/quote] Yes! Since the Pro reverb was new in 1965, this is the reason for the AA165 schematic for it, though it is identical (?) to the AB763 amp schematics, I believe. I’m going to recap the PS, and check the one old electrolytic cap a...

From what I can tell, the Pro Reverb was only the AA165, a different amp than an AA or AB165 bassman. Pretty much the same as a AB763 ____reverb amps.

https://schematicheaven.net/fenderamps/ ... _schem.pdf

It’s the speakers, for the most part. Plugged it into my Twins speakers, and was similar to my twins tone with the mid turned up a bit, though less bottom end. Still something a little off in the feel, like too much feedback or something. I didn’t isolate the circuit there to measure the FB resistor...

Stevem wrote: ↑Sun Dec 29, 2024 11:22 am I can’t see resistor drift making this amp sound honky especially since the tone circuit in these BF amps have a mid cut built in basically.
I would try the amp thru different speakers.

Yes that will be the easiest test over changing anything in the amp. Will report back my findings.

The “5%” tolerance PI plate resistors have drifted up ~20%, the grid load resistors >10%. Some other miscellaneous resistors have drifted beyond 20%, including the PI resistor on the cathode (which I know will affect the bias of the PI). The performance of this Pro…not noisy, but I would describe th...