'61 Ampeg R12-R Hum

[ca7922303]

Ground pin1 of the PI tube (V4), see if that kills the hum.

Haven't been checking for any output lately while trying to find a ground issue, but now I'm seeing that V1 socket is not lighting up any tube installed and no output. Anything with V1 socket could cause a hum?

[ca7922303]

Haven't been checking for any output lately while trying to find a ground issue, but now I'm seeing that V1 socket is not lighting up any tube installed and no output. Anything with V1 socket could cause a hum?

Nevermind the no output, found a broken wire on V1 pin 7. Have output again, same hum.

[SoulFetish]

You asked in another thread how someone could get killed? This is one example of how- grounding pins of a rectifier tube.

That's why, unless I'm trying to establish a DC ground point, the safest way to ground out circuit nodes when troubleshooting noise is using a large value/high voltage film cap, with one side connected to ground, and the other used as a probe. That way, if you inadvertently make a mistake and probe the wrong point, there is usually no damage done. (just make sure to discharge it after probing high voltage nodes, or it's gonna' hurt your feelings if you forget).

[ca7922303]

Ground pin1 of the PI tube (V4), see if that kills the hum.

To clarify, I did ground pin 1 of (V4) like you requested. I meant to say 6SL7 pin 1 to ground. Not real familiar with the tube numbers on vintage amps. I've gotten familiar with 6l6/el34/12ax7 and solid state rectifiers, not 5y3/6sl7/6sn7. Slip of the tongue.

[g1]

No hum with PI tube grid grounded means the hum is most likely from before that point.
It was not too clear earlier if you had tried it with all tubes in place except for V2, so try that now, or try it again if you had already done it. Make sure 'intensity' pot set at zero.

[ca7922303]

No hum with PI tube grid grounded means the hum is most likely from before that point.
It was not too clear earlier if you had tried it with all tubes in place except for V2, so try that now, or try it again if you had already done it. Make sure 'intensity' pot set at zero.

V2 removed, intensity @ zero, same hum as before. Only difference I hear is with volume on 10, the white noise is gone now.

[ca7922303]

V2 removed, intensity @ zero, same hum as before. Only difference I hear is with volume on 10, the white noise is gone now.

Just noticed, none of these tubes are labeled. Could wrong tube installed be possible source of hum?

[g1]

I guess it's possible. The numbers are usually on the glass. When they get rubbed off, sometimes you can still see them faintly with a magnifier.

With V2 still removed, ground the center lug of the intensity pot just to make sure the hum isn't coming down that wire.
Also move the wire around that goes to V4 pin 1. See if it has any effect on the hum level.

[ca7922303]

I guess it's possible. The numbers are usually on the glass. When they get rubbed off, sometimes you can still see them faintly with a magnifier.

With V2 still removed, ground the center lug of the intensity pot just to make sure the hum isn't coming down that wire.
Also move the wire around that goes to V4 pin 1. See if it has any effect on the hum level.

Had to step out. Be back on it shortly. Thanks.

[ca7922303]

I guess it's possible. The numbers are usually on the glass. When they get rubbed off, sometimes you can still see them faintly with a magnifier.

With V2 still removed, ground the center lug of the intensity pot just to make sure the hum isn't coming down that wire.
Also move the wire around that goes to V4 pin 1. See if it has any effect on the hum level.

(V2) removed, intensity center lug to ground, no change in hum.
(V4) pin 1 no effect on hum when moving around wire.

[g1]

Yes V4 pin 1 to ground does kill hum.

Now ground at the other end of the V4 pin1 wire, where it meets the board. Hum still gone?

(V2) removed, intensity center lug to ground, no change in hum.

Ground other end of wire from center lug of intensity pot (at board), hum still there?

[ca7922303]

Now ground at the other end of the V4 pin1 wire, where it meets the board. Hum still gone?


Ground other end of wire from center lug of intensity pot (at board), hum still there?

(V4) pin1 wire @ board to ground(no hum)
Intensity pot center lug wire@board to ground(hum).

[ca7922303]

(V4) pin1 wire @ board to ground(no hum)
Intensity pot center lug wire@board to ground(hum).

Im noticing that footswitch echo on/off is intermittent and although tremelo on/off works, when echo is on, tremelo button sounds microphonic when touched?

[ca7922303]

Now ground at the other end of the V4 pin1 wire, where it meets the board. Hum still gone?


Ground other end of wire from center lug of intensity pot (at board), hum still there?

What about disconnecting the footswitch(grey wire) connected to the 3 lug terminal in photo?

[g1]

It's worth a try. I thought that with V2 removed and it still humming this would eliminate the footswitch but try disconnecting it anyway.