73 Silver face Twin Reverb ?

[m-fine]

The AC on V3 is measured with no input signal?

[gtrplayr1976]

No input , everything set to zero .

[m-fine]

Where is that .14 volts AC coming from? The ground connection? It does not seem to be coming from the B+ or a signal. That could definitely be your hum source.

[gtrplayr1976]

Well...that pin connects to a 2.2K resistor, and I added a 25uf/25V bypass cap..looks like the other end goes to ground.

[m-fine]

Correct, so can you measure any AC at that ground point? That seems like the source of the noise.

[gtrplayr1976]

I'll check it out. actually I read .10 on V3 1/6 pin ,and .14 on #2/7 pin ..nothing at the ground side.

I'm going to recheck some of the AC voltages tomorrow, and correct the data I posted. I didn't realize such a small amout of AC would cause an issue...

[m-fine]

OK, that makes a bit more sense. If you have an AC signal on the v3 grids, it is going to show up on the annodes, go through the reverb tank and so on. It will get amplified just like the desired signal so a small AC can become a larger issue with each stage. If you turn the reverb volume up, does the AC signal show up on v4 and v6 and the noise increase?

[gtrplayr1976]

The reverb tank was not connected when I made these checks , but I get what you're saying...I think

[überfuzz]

I'm not sure we want that AC voltage in the reverb tube... Even if it's low it can cause the hum you're struggling with. You did the probing without any signal, right? I have a twin reverb, but I can't probe it now to compare the reverb tube.

See if you can spot any bad solder joints around tube 3. I'd keep an extra eye out on the ground connections.

[gtrplayr1976]

I just rechecked the AC voltages again ,and I'm seeing 1.35 VAC on pin 8 V1 & V2 , V3 I'm now seeing .28 on pins 2 & 7 , double what it was. First time I checked it this morning it was very near zero. V5 pins 1,2,6,7 show .09 VAC. I'm also seeing a voltage with just the ground connected .5VAC which zeros out when I put the positive to the chassis. I also noticed there's a little thing (technical term) off V5 connected to the intensity ,covered with heat shrink , I can see a small flash when I power up. I will check the solder joints and ground on V3 also.

Correct , probing done with no signal.

[gtrplayr1976]

OK..that voltage on V3 pins 2&7 is back to .12. I have also found some bad disc caps, or deteriorating anyway. I replaced two of them with orange drops same value ( guess thats ok?) I didn't have enough to replace all of them . I do have some smaller 400V that I could use 'but the discs are 1KV . I resoldered some places that may be suspect . I see ,or hear no differences with reverb tank connected . It really isn't the hum that's concerning me as much as the rattle sound from the speakers when picking the lower frequency strings although I would like to fix all the issues .

[dchang0]

Have you considered the very real possibility that the buzzing is mechanical? I had a bad buzz when the lowest notes on the low E string were played. Turned out to be a loose rear board (you know, those super-thin ones that partially cover the back). It was vibrating and buzzing like a reed.

Also, there were some loose washers on the reverb pan (mine is suspended in the bottom of the cabinet using springs as shock absorbers) that were buzzing against the tank's body. I used sticky-backed Velcro loop to insulate the tank from the washers, and the buzz went away.

Of course, the buzzing, though it was mechanical, did respond to the volume control--it got louder as the amp was turned up and quieter as the amp was turned down.

[gtrplayr1976]

I don't really think that's it , but I will look at that possibility closer. Thanks for the reply.

[überfuzz]

Just plug the amp to a different speaker. If the rattle stops... well you figure it out.

It's hard to keep track of the issues here... Have you nailed any of the noises yet?

I actually did the same with my tremolo. Replaced all the disc caps with orange drops. It worked like a charm.

Edit, I wouldn't use a smaller cap. It's nice to have some margins.

[gtrplayr1976]

I've tried a different speaker, same thing . I haven't found anything that I can say was THE problem .

I replaced all the caps I could with what I have , but I don't have any 1KV orange drops ....400 ,and 600 , but all .01 I could order more to replace the others. I have some other orange drops around , but different values...maybe some .02, or 03 ?

I did reset the bias last night. I did notice that noise in general hum ect. was almost non existent, and I cranked the volume. Of course no input signal.. I need to try it out today to see if there's any differences.