Premier 90 Reverb Unit

[musipol]

@amplexus
Your explanation does make sense. Safety ground is not disturbed.........and this additional circuitry merely limits ground currents through the 0V reference. It intuitively seems safe provided diodes and resistor don't fail open. I use high current bridge and 10w, 10 ohm resistor, 600V cap as a precaution. Thanks for your input.

 

[inkster]

I was able to quiet one down by completely recapping and correctly orienting the film caps, had to alter the heater supply wiring slightly but I don't recall what I did exactly.

 

[JohnRoberts]

that Red C penciled in might be the lag that is causing the stage to be too slow and rectify the RF. I ASSume the rectification is occurring in that first stage,

JR

 

[luthierwnc]

Hi All,

Please forgive a new member resurrecting a zombie thread on my second post but this seems the right place. I’m going to rehab a friend’s Premier Reverb 90 back to working condition. Right now all you hear is dead filter caps. The unit is in good shape. Other than a few mouse turds there wasn’t any corrosion or heat damage. The pots work. All the signal caps and resistors register surprisingly close to spec. Cab’s on the high end of what you’d expect. Tank and tubes seem OK.

There’s no time or price rush on this and it doesn’t have to be collector condition. Safe and quiet is the goal.

In reading here, the AmpGarage, Gearpage and NoiseMikers I found a wide variety of approaches. That gets even more complicated because my chassis is a completely different layout than the ones shown in this thread – older, I think, and unpainted like CJ’s second project.

I thought I’d do this in stages starting with new filter caps, signal caps and metal-film resistors. Those will be grounded more like the hybrid schematic from NoiseMikers with separate star and chassis points. I’ll put in a bridge rectifier too.

If that goes well next comes a three-prong cord, fuse and new footswitch cable.

Now that this has been up a while I was hoping folks would chime in about what mattered and what didn’t in your versions particularly:

a) is using a 12AX7 an improvement (I have a few),

b) is the ground-strip isolation network effective or would a little transformer work better,

c) is having the switch on that pot a noise headache,

d) would you stick with the component values?

One thing I could do with this weird chassis is cantilever a daughter-board under the pots and jacks for working room. Shielding the plywood also came to mind.

Thanks for looking, Skip