73 Silver face Twin Reverb ?

[überfuzz]

Can mean a bunch of things, but first bed is a bad filter cap. Or... maybe a bad solder in a newly replaced filter cap... Did the buzz appear after you fired it up after replacing the old filter caps?

[gtrplayr1976]

Yes it did, but I didn't hear the amp before. It belongs to a friend.

[überfuzz]

Ok. Just to rule out the filter. Check the filter if you're not 100% on the soldering/wiring job. (Did you test the caps in any way before you mounted them?) If the filter is bad you might see some AC voltages in the power socket.

[52 Bill]

How did you set the bias on the amp?

[m-fine]

If the amp is stock, the bias adjustment is a balance between the tubes, with no real bias adjustment. I would fix that.

You can pull the first reverb tube and the trem tube to rule those sections out. I would also pull the reverb tank RCA connections. The simpler the circuit in play, the easier it will be to track stuff down.

Sniffing for AC signals on the B+ and B- (bias) would be my next step. Did you replace the bias filter cap?

[m-fine]

Oh, if you have not done so, relace the cathode resistor on the reverb driver tube with a larger value. It is probably not your problem yet, but it will be.

[gtrplayr1976]

How did you set the bias on the amp?

Hey Bill.. I added a bias pot, and used a probe.

[gtrplayr1976]

If the amp is stock, the bias adjustment is a balance between the tubes, with no real bias adjustment. I would fix that.

You can pull the first reverb tube and the trem tube to rule those sections out. I would also pull the reverb tank RCA connections. The simpler the circuit in play, the easier it will be to track stuff down.

Sniffing for AC signals on the B+ and B- (bias) would be my next step. Did you replace the bias filter cap?

Yes , all major caps were replaced.

[gtrplayr1976]

Oh, if you have not done so, relace the cathode resistor on the reverb driver tube with a larger value. It is probably not your problem yet, but it will be.

How much larger ? and wattage ?

[m-fine]

Look at the black face circuit as an option. That one used 2200 with a 25-25 bypass cap as did early silver face models. My silverface came with a 470 which drifted even lower, and that translated to too much current in the 12at7 and frequent destroyed tubes. The later 135 models decreased the transformer HV from 440 to 395 and increased the cathode resistor to 680. Without looking at a tube chart, my gut would be to go with at least 1500 there if your voltage on pins 1&6 is over 400 volts.

[gtrplayr1976]

This is one of the Master volume/boost Twins..I'll do a little comparison on the two amps. ...component wise. Thanks

[gtrplayr1976]

Look at the black face circuit as an option. That one used 2200 with a 25-25 bypass cap as did early silver face models. My silverface came with a 470 which drifted even lower, and that translated to too much current in the 12at7 and frequent destroyed tubes. The later 135 models decreased the transformer HV from 440 to 395 and increased the cathode resistor to 680. Without looking at a tube chart, my gut would be to go with at least 1500 there if your voltage on pins 1&6 is over 400 volts.

V3 right? What if I added a higher resistor ,and the bypass cap ?

[m-fine]

If it was a MV model the factory resistor was likely 480 plus or minus 20+% (optimistically labeled 10%) but it could have been replaced over the years.

[m-fine]

3 rd tube from the right when looking at the back of the amp, should be a 12at7. The resistor should be on the board fairly close to the tube, but I would have to look at the layout to find it. Just follow the wire from pin 8.

[gtrplayr1976]

cool..thanks...I have the layouts already