Fender Pro Reverb, Reverb hum and hiss (Pro Tube Series 2001)

[kekke]

Hello everyone, it seems a very common topic but when I dial the reverb up in my Fender Pro Reverb (pro tube series 2001) there is a huge amount of hiss added.
I decided to call out for help since I really would like to make this amp more usable.

I already solved the hum problem on the reverb for the most part...but the hiss just seems too loud to be acceptable and I want to get to the bottom of this.
For some reason I hear lots of people complaining that the amp is very noisy at idle, if someone has experience with this amp or tips that I could try to lower the noise level on the clean channel, I am all ears.
It does not bother me all that much that it is a bit noisy on the clean channel, but with the reverb added the hiss added is just unacceptable to me.

I am using new tubes right now and V1 has a 7025 in there that sounds very nice to me. I am not using the gain channel at all, neither the fx loop.

Until now I was able to lower the general noise a bit by using a NOS Mullard CV4024 tube for V7. In any case it was better than EH12AT7 tubes and I tried many brands. For the PI I am also using a NOS Mullard CV4024.
Surprisingly when I took the reverb tank from the cabinet the 'hum' that was induced was caused by the PT. So the 'hum' problem decreased greatly, I also shielded the reverb tank from the bottom and that also dropped the hum further. Yet I cannot get rid of this 'hiss' and to me it is just too loud to be acceptable and I also have this feeling that the reverb does not sound as deep as it should, I cannot get any drip at all out of this amp.

So until now I have tried this to get rid of the hiss and hum with some success:

-Shielded the bottom of the reverb tank (repositioned it).
-Installed high quality shielded cables
-Tried a different tank (same impedances, had the exact same hiss)
-Retouched all solder joints on the PCB to prevent this to come from cold solder joints
-Checked all grounds
-Checked all shielded wires in the amp.


The hiss increasing with the reverb pot probably tells me it is before it in the circuit, what should I do next?
For convenience this is the amp model and schematic:

http://ampwares.com/amplifiers/fender-pro-tube-reverb


Thanks in advance for help!

[Chuck H]

Hiss is a byproduct of gain. Reverbs require a huge amount of gain because the signal from the tank is tiny. That said... Some tubes hiss more than others. Do try different tubes to see if you just happen to have a noisy one (or two). I've had so many noisy tubes, brand new out of the box, that I always suspect a noisy tube first in these situations. If that doesn't give you any joy the only thing I can suggest would be a bleeder cap on the reverb recovery stage. The right value would reduce hiss, but may bite into the reverb sparkle just a little. This is a very common problem. I actually have an amp build that I need to solve this same problem for. It's in a customers hands now so I don't have it on the bench. He uses very light reverb and has no complaints. I have a compulsion to feed though Trust me. This is really, really normal. New reverb tanks also seem to be noisier than older ones too (buzz, not hum or hiss). A careful circuit that bumps top end below a certain cut frequency on a filter is probably the best compromise. If any of this goes over your head, take the amp to a tech or turn it in for warranty service if applicable.

[Lydian]

I'm having this exact problem on my 68 reverb. Same hiss. I don't use much, when the amp acts normal, I use 2.7-3 on the knob which is plenty. Now I crank it to 10 after just being turned on get very little reverb. After the amp is on for awhile it seems to turn to pure hiss.

Any new opinions or recommendations amigos?

[52 Bill]

I'm having this exact problem on my 68 reverb. Same hiss. I don't use much, when the amp acts normal, I use 2.7-3 on the knob which is plenty. Now I crank it to 10 after just being turned on get very little reverb. After the amp is on for awhile it seems to turn to pure hiss.

Any new opinions or recommendations amigos?

Are you talking about a 68 Princeton Reverb?

Why not start a new thread for your problem. In any case the first thing to do is to change the reverb recovery circuit tube.

[Lydian]

Are you talking about a 68 Princeton Reverb?

Why not start a new thread for your problem. In any case the first thing to do is to change the reverb recovery circuit tube.

68 Pro Reverb, and will do.