Do '65 Twin Reverbs (Reissue) Just Sound Bad?

[Buddha's Guitar Tech]

Does this amp just sound bad out of the factory?

When the Vibrato channel is turned all the way down, i get a little noise. If i turn it up just a tad, that noise goes.

Turning either channel up, with a guitar connected (guitar turned all the way down) there's a ton of noise.

Here's what i've done so far:
- Moved the AC ground screw further away from signal ground
- Ran the heater ref pot wiper off its chassis point and directly to the AC ground
- Balanced the heaters evenly.

Perhaps i should be dressing signal cables? It's not what this amp was in for, so i don't really want to go to town and not charge for it - more for my own curiosity at this point.

And oh great, now i can hear something dying. Wonderful.

[Prairie Dawg]

Hmmm. Every one I ever worked on benefits from getting the bias out of cold to a more normal range, and some careful selection of preamp tubes. That's where I'd start.

[billyz]

Could be Plate load resistors. Some of the early ones had bad control pots, but you would find that easy enough. Should we assume you tested for noisey tubes ? I recently had a bad cathode resistor cause a lot of noise.
Can you isolate it to one section or stage ?

[kevster]

Yes, they are all horrible and beyond help. I will gladly dispose of it for you if you ship it my way...

Sorry, just too tempting this morning.

"Quirky" is my experience...

[selloutrr]

The pcb fender reissue amps often are slapped together in such a hurry they miss soldering points.

If in doubt retouch all solder points and correct the bias. Tubes also make a world of difference.

Once gone over the amps can be reliable and sound very good.

[Buddha's Guitar Tech]

The noise i'm getting is not the typical plate resistor noise, it's a hum, reminiscent of a ground loop, or RF from the heaters. i do think dressing some signal wires would help for a start.

Can of worms, grumble, can't let it leave the shop sounding like crap, grumble.... doing it to myself again, grumble...

Re-soldering sounds like a good idea.

[Teleguy61]

The pcb fender reissue amps often are slapped together in such a hurry they miss soldering points.

My experience also.
Poor solder joints, particularly around the output tubes.

[Buddha's Guitar Tech]

Hurrah, found the problem. Despite having CHECKED AND SET the filament balance pot earlier, i found, when i went back to it, it had drifted wildly.

What i believe caused this amp to fail in the first place was a screen-heater short. Evidence: burnt screen resistor, blown 10A fuse in the heater line. i think that's enough cause to replace the 100R pot.

i think i'll install two 100R resistors instead - anyone any ethical concerns over that?

[sharkboy]

Well, that's the way I would have designed it, but if you do that, you'll be the amp tech who made it lose value and gets sworn about- not that reissues are supposed to be terribly valuable. Minimally, if you do it, you should disclose that. It would grate on me, but I suppose I'd get a replacement pot for it.

[Phil_S]

i think i'll install two 100R resistors instead - anyone any ethical concerns over that?

I don't do this sort of thing for a living. I'm an accountant and we have our own rather stiff standards of ethics (not all follow them). These, I think make for good general business ethics. I suggest the following:
1) two 100R resistors are an upgrade compared to whatever cheesy pot it came with and
2) you are obligated to explain/tell the customer and do it without being salesy about it.

Disclosure is the all important aspect of making it ethical. Once you disclose and give the customer a choice, you are out of the woods. If you just do it, then, even if what you did was an improvement, the customer might not understand and can come back with a complaint. No surprises and I think you are home free. What's holding you back from phoning the customer and taking 5 minutes to find out his preference?

[Buddha's Guitar Tech]

i do have a 100R pot, but not the same type - mine has the shaft while Fender's is the inner-slot type.

i could always leave the dodgy pot there and use its ground lug as a... ground lug.

Thanks for the viewpoint though, hadn't thought on those terms. i'm not precious when it comes to filament balance, but i'll ask the customer.

Something tells me he won't care, but i'll make sure.

[Buddha's Guitar Tech]

In a surprising twist, owner wants the original-type replacement.

And there you have it.

[tubeswell]

If if was me I'd be strongly tempted to gut the amp and rebuild it vintage style (keeping the PT, OT, RT, Pan, chassis, faceplates and tubes (and of course the cab)

[Buddha's Guitar Tech]

Oh me too, but it ain't my amp.

There certainly is a lot of useable space.

[tubeswell]

Sell him an upgrade then