Premier Reverb 90 hummm

[hylaphone]

Anyone here successful taming hum in one of these units?
The couple I've heard were inherently noisy, bad layout, half-wave rectification, etc.
Short of reworking the whole layout, any tricks to these?

One here has new e-caps, fresh tubes, elevated heater CT... and tried everything I can think of to quiet the 60Hz hum.
Certainly ground loop issues, I'm not sure how to tackle that without isolating all signal grounds.. a real PITA

[drewl]

Funny, I rebuilt two in the past couple months.
the first was a bitch to get quiet, the second one was dead quiet.

I think using individual filter caps on the second one made it alot quieter than the multi-cap replacement from AES on the first.

Make sure you have a good ground connection to the chassis, sand it down to fresh clean metal.

I installed a three prong grounded cord and installed fuses in both for safety.

[hylaphone]

Indeed, the new caps are individual. Fused and grounded power cable.

With output plugged into an amp, the unit causes hum even with the power off. Unplug its power cable and the hum goes quiet.
Turn it on and the hum increases as I dime the reverb control.

[hylaphone]

Well, I had to "lift" all signal and power supply grounds - isolated the jacks/pots and did the old resistor-cap-anti//diodes to gnd trick and the unit is now dead quiet.
Sounds pretty damn good too!
Ground scheme is buck wild in these, if I work on another I will skip right to this measure.

[pontiacpete]

isolated the jacks/pots and did the old resistor-cap-anti//diodes to gnd trick and the unit is now dead quiet.

Would you mind explaining this? I'm working on one of these again.

[hylaphone]

Sure - just isolate the input jacks and reverb knob and run all signal and power supply grounds to a single point, which is "lifted" above chassis ground by a 10r resistor, .1uf cap, and some anti parallel diodes. I used a 35A bridge. Power cable ground is the only direct connection to chassis.

[stereomonostereo]

I've worked on a bunch of those. Some are noisier than others. Another thing to check out is the combination AC ON/OFF, Volume pot. Moving the AC off of that usually cuts down on the noise a bit