Vintage Deluxe Reverb (December 1965) low output

[jordan86]

LOOOONG time no post here. I have some good news though.

I just took possession of a new friend's 1965 Fender Deluxe Reverb. DEAD stock. Only thing that I can detect that has ever been done is that it has an added 3 prong power cable and one replaced screen resistor. Has all new tubes. The new friend said the normal channel was quiet and thought it may need some work/new tubes.

I brought it home and fired it up and it sounds KILLLER. The normal channel seems slightly quieter than the VIB channel, but I think that is typical on the AB763?  Aside from scratchy pots, it seems quite functional, despite the all original condition (caps, etc).

Anyway, I dropped the chassis and did some minor check ups and cleaning and now the amp seems even quieter. And both channels now. Like they BARELY break up on 10. Definitely quieter than my Princeton Reverb build (mind you my Princeton has a 12" speaker, a stokes mod, and an Allen amps 20W OT). It's not the speaker. I've A/B'd speakers to make sure speaker efficiency isn't a major factor.

Any thoughts on what I did pulling that chassis? FWIW here's a recap of what I did:

- I cleaned the pots with some MG 404B Contact Cleaner (w/ silicone)
- I clipped the death cap out
- I measured resistors (all within 10-15% of spec)
- Check voltages: All within 5% of spec
- I cleaned the three octal sockets with deoxit (6v6s & 5AR4)
- Checked bias: 435v on plates. Power tubes measuring at 20 and 24ma. (8.9w and 10.5w pd) Not a terrible mismatch.

I'm new to the MG contact cleaner. Someone recommended it to me over DeOxit. I do have plenty of deoxit on hand too though. Can the added silicone be a problem?

I did try some other good 6v6s from my Princeton and not much difference.

The amp is very quiet. No hum or hiss otherwise. Anything I am missing?

[Dave]

Yes, its normal for the normal channel to be slightly quieter.


I would think that coating the resistive surface of the pots with silicone would be bad joojoo. I'd probably try to clean that out.


Does it have the original filter caps? I wouldn't even turn it on if they are still in it.


Dave

[OldGuitarPlayer]

I think I would agree with Dave about the filter caps, I would replace them asap if they are original. Also there's probably an electrolytic in the bias circuit I'd replace. I know that amp has reverb and tremolo, those can sometimes give issues - don't know if you have the switch, if not you can make one so you can switch those in and out. I've also heard of shops getting those in where the pre-tubes are all mixed up, I believe there are two 12AT7 tubes and four 12AX7 tubes. It would be cool if it were the original tubes though! Cool find!

[jordan86]

None of the glass is original.

[Latole]

Checked bias: 435v on plates. Power tubes measuring at 20 and 24ma. (8.9w and 10.5w pd) Not a terrible mismatch.

Mismatch is not bad. I leave it.

As say before; replace all filter caps with F&T caps
Bias filter cap and by pass filter caps too

[shooter]

The amp is very quiet. No hum or hiss otherwise. Anything I am missing?

tech note;
you seem to be using "quiet" to describe both good AND a bad, maybe switch to "low output", "loss of volume". for the bad.


am I right, the output was good when you got the amp, you cleaned, you lost volume?
IF SO;
with some audio jacked into the amp at around 3 on the volume, slowly push down n kinda "rock" the tube in a circular motion...PREAMP only for now, so stop at the PI, stop when they tubes are too hot to play with.
easy touch, no MMA stuff

[jordan86]

Hey guys! I believe I've solved this...

Replaced all the electrolytics. F&T on filter/bias, and Sprague on the bypass caps. No improvement. Lifted a few coupling caps to test for leaks. No leaks. Also, did some of the other recommendations given here (tube rocking), etc. Stumped!

In the process of soldering my PI coupling caps back in, I did another triple check on things and discovered a poor ground connection on the Phase Inverter section. The bare ground wire was just sorta resting on top of the pool of solder on the grounding plate. Crazy that it's been like that for 60 years. I nudged it ever so slightly and it broke completely free. Got it soldered back in well and she rips now!

Amp is quite LOUD now, as in volume and output ;)  Noise floor (hums/hisses) is still pretty good. Nothing worth chasing at the moment.