Fender Pro Reverb AA165 distorted Bass Notes

[Platefire]

I've always thought I would enjoy running sound but I was always occupied in lead guitar or occasionally bass slot. Knowing how bands work(especially the lead singer) , I could see that it could be a very uncomfortable position to work.

[Dave]

I'm wondering if you are not simply swamping out the reverb pan. How does the reverb sound on around 3 or 4 with your hearing aids in?
Some observations that I have about the reverb circuit... May not have anything to do with your problem...
Cathode ground on reverb return is prone to ground loops. A loud enough hum from a ground loop "could?" be related.
Sometimes a 12BH7 sounds better as a reverb driver than a 12AT7.
Sometimes the springs on a really old tank can get a little loose and flabby and make it easier to swamp out.


Dave

[tdvt]

BTW - don't ever volunteer to run the sound. Every band member wants it different.

Somehow, I was always the default sound guy (from the stage)  Thankfully, most of the guys over the years were reasonable....but not all

Just ran some quick voltage checks/guitar test on my Pro. My rattle/distortion is NOT reverb circuit-related, but in the process I found some significant board leakage, in spite of extensive cleaning & de-waxing. Thought I had that addressed, but apparently not.


Seriously considering just building a new board for it & moving everything over.

[bmccowan]

Fender boards - As I understand it, the original problem was moisture in the boards. And then Fender "corrected" it by waxing the boards. So now we are dewaxing the boards. What is to keep the moisture problem at bay, I wonder? Is there another product that might seal the board after dewaxing? It would need to have a high melting temp and be non-conductive. I see that folks melt and clean the wax off, and then finish up with isopropyl. I think it is down to bare cardboard at that point.

[Platefire]

   This is what my Pro board looked like when I got it. As you can see, a real mess in more ways than one. The guy that sold it to me believed it would never work again without a new board. Not only was it filthy but wavy as the sea.  As I remember, I cleaned this one with Isopropyl. I never have detected any conductance through the board. It's really working right now like I always wanted it to.


Dave--I think you are referring to me? Yes, if I have to do any serious critical listening with my hearing aids in because of not only the volume loss but treble/highs loss. Previously before I changed out a lot of parts, when you turned up the reverb up it added serious amounts of gain to the signal plus more humm. Now I can detect an ever so slight amount of gain, not enough to bother with. The reverb just gets deeper when you turn it up now, with no hum.

[tdvt]

Those are some scary pics!

I have 0 to a few mV DC in some areas, but I was seeing 3V± in the bad sections & was able to induce noise into the circuit by scratching the board with the meter probe.

Visually, the bad areas look as clean as the good sections & had similar heat gun/iso bath treatments.

If I have to depopulate the board for real cleaning, I am thinking I'd rather just move stuff onto a new one & would probably use some garolite/bakelite sheet that I have in stock from making tele pickguards.

That stuff is a similar thickness to the original eyelet boards but seems to be much more stable.

[Platefire]

I think I used Q-Tips, tooth brush and Isopropyl Alcohol to work around under everything on the board. It was pretty painstaking but I was just determined to make it work.

[tdvt]

I took custody of a second '79 UL Pro Reverb yesterday & while not nearly a waxy as the first one, it too, has significant board leakage.

I am seeing around +2V on the board near the preamp tube B+/100K eyelets.

On the little rectifier board that the bridge rectifier lives on, I am seeing +5V to +6V, well away from any eyelets.


This one is completely untouched inside & in spite of the old original e-caps & the board leakage, is essentially fully functional (other than weak trem) & surprisingly quiet.

[Platefire]

Me, being that it's operating without any problems presently, I would clean those areas with Alcohol and then dry it out with a hair dryer and call it good.I would check resistors, coupling caps and definitely change filter caps being 30+ years. On the Trem---put in one of sluckey's Tremenators--they nice and clean,  no ticking and no more bugs to change out

[tdvt]

Me, being that it's operating without any problems presently, I would clean those areas with Alcohol and then dry it out with a hair dryer and call it good.I would check resistors, coupling caps and definitely change filter caps being 30+ years. On the Trem---put in one of sluckey's Tremenators--they nice and clean,  no ticking and no more bugs to change out

I will admit I am torn; on one hand it is working, on the other hand, for how long?

I am guessing that it was left for dead a while ago. I received it in pieces, directly from the storage locker & there was no sound when I first put it on the LL. But just a couple broken coupling cap leads. Replaced those parts & off she went.

I actually haven't finished the first one to my satisfaction (occasional static I am attributing to the noisy board) so probably best NOT to go to deep on this one yet.

Don't know if you have ever checked out Brad's Guitar Garage on YT. He's been up to his eyeballs on a few different silverface rehabs with some rather intensive board cleaning, seems to be a thing with this era amps particularly.