Princeton Reverb Help

[Valvehead]

Ive got a PR that has a low freq. hum. sounds like its around 160-200hz

Ive done a few things :

checked volts and bias
swapped all tubes

the hum is not affected when i short V1 pin 2 ... V2 pins 2/7 .V3 pin 2

it reduces the hum a little when i short V1 pin 7

it kills the hum when i short V3 pin 7 --amp gets quiet

having the reverb tank plugged in has no affect
turning the rev pot changes the hum a bit, but doesnt really kill it or drastically reduce it..

its there with the Volume on 0 , turning it up the amp and hum gets louder .

i swapped 3 caps right before that stage (v3 pin7 ) = .022 , .003 , 10pf .

i tried moving the wires around

is this stage supposed to have a shielded cable? all the wires are new cloth style

all the caps were replaced in 2003

i found the 2 100 ohm heater resistors near the light were burnt, i replaced those .


any ideas ?

[tubeswell]

So you swapped the V3 tube already?

[Jazz P Bass]

The fact that the caps where replaced in 2003 does not verify that they are good.
Break out the voltmeter & measure the Vac ripple of each stage of the B+.
Sounds like one or more caps went south.

[Valvehead]

yes V3 swapped -- BUT -- i did NOT swap the rect tube yet. I had to order one last night.

jazz- is that just AC to ground ?


I clipped in a new 47/450 cap at each terminal of the can cap. At one of them it GREATLY reduces the hum , the others it helps a little--- so it looks like i need a new can cap !





A side question: the main can cap is a 20/20/20/20 .........would a 40/20/20/20 be ok in this circuit ?

[pontiacpete]

That's the one I've used and worked fine.

[Jazz P Bass]

yes V3 swapped -- BUT -- i did NOT swap the rect tube yet. I had to order one last night.

jazz- is that just AC to ground ?


I clipped in a new 47/450 cap at each terminal of the can cap. At one of them it GREATLY reduces the hum , the others it helps a little--- so it looks like i need a new can cap !





A side question: the main can cap is a 20/20/20/20 .........would a 40/20/20/20 be ok in this circuit ?

Yes. Vac to ground.

Personally, I would simply tag on the cap that reduced the hum.

I have spent good money on the multicans only to find on more leaky. (ie: hum)

[Valvehead]

thanks guys !

[pops]

I used to tag caps on a can until one shorted now i take it out of the circut. Replacing the can is best as one bad cap is as old as the rest and will go south soon. If you don't want to replace the can, use individual caps, but do one do all and replace the bias cap also it is most likely older than your filter caps as it gets missed a lot.

[pops]

I used to tag caps on a can until one shorted now i take it out of the circuit. Replacing the can is best as one bad cap is as old as the rest and will go south soon. If you don't want to replace the can, use individual caps, but do one do all and replace the bias cap also it is most likely older than your filter caps as it gets missed a lot.

[Valvehead]

got a new can on the way pops !