Princeton Reverb - Reverb Noise

[Bombacaototal]

I would mount the 220K directly on the return jack. Just let the jacks use their own self grounding (no insulating washers) and don't run any extra ground wires to the jacks. Maybe that will work. It did for Leo.

Done as suggested. Unfortunately no difference

Is it worth attempting the isolation washers or is the ground loop is probably coming from elsewhere

[sluckey]

Is it worth attempting the isolation washers or is the ground loop is probably coming from elsewhere

Remember the gator clip test? The results indicate the hum originates in the recovery tube. Insulating washers should not make any difference.

I went through this with my TDR (Deluxe Reverb) build several years ago. My cure was rolling tubes in the recovery tube socket. I ended up using a 5751. I do recall a guy that had hum problems that appeared to come from the recovery tube but were actually caused by the 12AT7 driver. He swears that another 12AT7 was his fix. Didn't seem logical to me but sometime hum issues can be very illogical. Try this. Disconnect the tank cables from the amp and use a gator clip to ground the return jack. You should still have hum with the reverb pot turned up. While listening to the hum, pull the 12AT7 driver tube. Any difference?

[Bombacaototal]

Is it worth attempting the isolation washers or is the ground loop is probably coming from elsewhere

Remember the gator clip test? The results indicate the hum originates in the recovery tube. Insulating washers should not make any difference.

I went through this with my TDR (Deluxe Reverb) build several years ago. My cure was rolling tubes in the recovery tube socket. I ended up using a 5751. I do recall a guy that had hum problems that appeared to come from the recovery tube but were actually caused by the 12AT7 driver. He swears that another 12AT7 was his fix. Didn't seem logical to me but sometime hum issues can be very illogical. Try this. Disconnect the tank cables from the amp and use a gator clip to ground the return jack. You should still have hum with the reverb pot turned up. While listening to the hum, pull the 12AT7 driver tube. Any difference?

Thanks sluckey. I did exactly as instructed but unfortunately no difference. Maybe I also checked the grounding on both pots

[pdf64]

Fully bypassing (ie well below mains freq) input stage cathodes cab be beneficial for signal to noise ratio, ie minimising hum and hiss. The reverb recovery stage may be regarded as an input stage.

[Bombacaototal]

I removed the cathode cap of the reverb recovery. Indeed an improvement as far as noise but as you said weaker reverb, and also the frequency reponse seems to have changed slightly. I still prefer the sound of the reverb with the cap but I cannot stand the noise floor, so will leave the cathode without the cap for now.

I also just bought a low noise 7025. Cannot wait to try it out. Hopefully that will do it! I will report back as soon as I have it.
https://www.watfordvalves.com/product_detail.asp?id=684

Many thanks again for the help.

Forgot to report back. I tried the low noise 7025, and noticed an improvement, maybe 10% or 15% less noise but overall the noise floor is fairly high. I think the only option left is having the amp without the reverb recovery cathode cap, even if it sounds less nice overall.

[TUBEDUDE]

Still sounds like a grounding/sheilding issue if the noise/hum level is so noticable as to require circuit modification to be useable.

[Bombacaototal]

Still sounds like a grounding/sheilding issue if the noise/hum level is so noticable as to require circuit modification to be useable.

So I played around with different reverb pans, and also different grounding options on the pan itself. They are usually only grounded on the return (red) but for some reason I get the least amount of issues with both send (Black) and return (red) grounded inside the pan on ones of the 3 pans I tried.

Still there is issue, and below is an audio of master at 3 o’clock (I added a dumble style master on mine) and you can hear me turning the reverb pot up and down. I am using the least noisy of the 3 pans with send (Black) and return (red) grounded inside the pan.

[norburybrook]

Still sounds like a grounding/sheilding issue if the noise/hum level is so noticable as to require circuit modification to be useable.

So I played around with different reverb pans, and also different grounding options on the pan itself. They are usually only grounded on the return (red) but for some reason I get the least amount of issues with both send (Black) and return (red) grounded inside the pan on ones of the 3 pans I tried.

Still there is issue, and below is an audio of master at 3 o’clock (I added a dumble style master on mine) and you can hear me turning the reverb pot up and down. I am using the least noisy of the 3 pans with send (Black) and return (red) grounded inside the pan.

that's not right definitely. I Built a princeton reverb recently in a wreck chassis, I had to mount stuff where I could and it's all in reverse etc but it's quiet, that noise sounds like a trainwreck express!!!!!! which you would expect something definitely squirely with your amp but I'm afraid I can't help with what that is...sorry


M

[tubeswell]

Is this a head? or a combo? (How close is the pan's output transducer to the PT?)

[Bombacaototal]

Is this a head? or a combo? (How close is the pan's output transducer to the PT?)

It’s a head and I’ve tried with the pan as far from the amp as I could.
I think there is still a ground loop or cold solder joint somewhere

[tubeswell]

So did you turn the pan around so that the output transducer was away from the PT end of the chassis?

[Bombacaototal]

So did you turn the pan around so that the output transducer was away from the PT end of the chassis?

Yes, I tried with the reverb pan at about 2 meters away from the amp

[pompeiisneaks]

I literally had to play with the reverb pan on a Reeves Space Cowboy because it was causing hum, I ended up twisting it slightly off axis and adding in extra cardboard on the bottom of the reverb bag to create a bit more 'noise cancelling' before I got it to a 'semi decent' level. It can be quite a PITA to get reverb pans inside the cabinet, to not hum. As soon as I moved it outside the cabinet, it went dead silent.

~Phil

[tubeswell]

I think there is still a ground loop or cold solder joint somewhere

Ground loops are a nuisance in reverb circuits (because the S:N ratio is particularly important in the recovery stage). Where have to got the reverb recovery stage grounded?

(I presume you've re-flowed all the joints?)

[Bombacaototal]

I think there is still a ground loop or cold solder joint somewhere

Ground loops are a nuisance in reverb circuits (because the S:N ratio is particularly important in the recovery stage). Where have to got the reverb recovery stage grounded?

(I presume you've re-flowed all the joints?)

My reverb recovery cathode is grounded at the buss bar which goes to a star ground washer near the input. It's supply is also grounded at the same place (ie star ground washer)