Peavey Express 112 teal stripe - preventive maintenance and mystery...

[Pixel]

I just picked up this nice amp, everything works fine except the high gain input. The chassis actually has a little bend in it right where the jack is so I expect it had a big bump at some point. The chassis is also bent a bit where the PT is so it probably got dropped as well.

The mystery around this amp is the speaker. It isn't stock and is apparently an RSC. The nice fellow I got this amp from has had it since it was newish, and didn't know the speaker wasn't original. The speaker code on it is DWF5 7383 and date stamp is August 20, 1975. I found that a pair of these speakers were OEM for the Traynor YGL-3 Mark 3, which is a 100Watt tube amp. Now I am not going to be diming this Express, but I have a teenage son so...yeah. Is this speaker going to be okay with the 65 watts this Express can put out?

All the caps test really well for ESR. Barely higher than the figures on the Blue ESR meter chart. Most of the caps are axial Nichicons, with a few Illinois here and there. Usually when I check out an old amp at least a couple caps will have high enough ESR that I feel I should replace them just because I'm in there, but not this time. I'm impressed with this thing.

I am wondering why 4 out of 5 of the RC4558P are socketed. Why wouldn't they socket all of them? I notice that some folks roll the op-amps in Bandits. I do happen to have some NE5532s and OPA2134PAs sitting here feeling lonely. Should I pop a couple in, if so where?

Is there any preventive maintenance I should be doing while I have this all apart?

[TomCarlos]

I can address the speaker. I believe the stock speaker for this amp was the Peavey Blue Marvel 707-77104. This was made by Eminence, 12" - 8 Ohms - 75 watts.



Express_112_Teal.pdf

[Bill Moore]

I have gone through a few of those old Peaveys, and generally change all the opamps to OPA2134A except the reverb. The low noise chips seem to "sweeten" the sound, but in the reverb circuit, I prefer the 45??'s sound. I'm curious what you think of the NE5532's.

[Pixel]

I reflowed the solder on the input jacks and took the bends out of the chassis. I think the bent chassis was torquing the high gain input jack and causing it to lose contact as the solder seemed fine. All of the jacks were super dirty and got a good cleaning. The high gain is fine now.

I tried the OPAs everywhere except U2 which was soldered in. Right now I only have an OPA in U1 because that is the one that seemed to make the difference.

Next year I think I will DIY a tank bag for the reverb just for something to do.

Thanks for the help.

[Bill Moore]

I traded for one with out the reverb cable, ended up using 2-2 conductor Molex connectors with some "Fender style" cable I had. I ended up taping, (insulating) the cables, as the circuit has the ground lifted!

[J M Fahey]

I have gone through a few of those old Peaveys, and generally change all the opamps to OPA2134A except the reverb. The low noise chips seem to "sweeten" the sound, but in the reverb circuit, I prefer the 45??'s sound. I'm curious what you think of the NE5532's.

Modern Op Amps in general are better than old ones but for some unknown/undocumented reason, older ones are preferred by many respected manufacturers to drive reverb tanks.

Marshall kept old obsolete lower specs LM1458 for that duty, (not a typo, not 4558) although they were using Industry Standard much better specs TL072 elsewhere.
Not sure but guess Randall did the same.
And maybe MusicMan.

There must be some reason for that, I do not believe in Mojo and such,

My laziness and procrastination delay me but one of these days I will protoboard a generic Op Amp reverb drive circuit, load it with the proper tank, of course, and drive it to clipping while rolling different Op Amps ... including 1458
I would not be surprised at finding it can (undocumented) supply more current, or be more stable driving heavily inductive loads or something.

Marshall replaced it with two or three parallel TL072 sections, maybe that is a clue.