Marshall Lighted Rocker Switch hookup-Bias problem solved!

[sluckey]

Your voltage readings are not consistent. Measure again with probe directly on the tube pin. Give us readings for V1, V2, and V3. We need six readings for each tube, pins 1, 2, 3, 6, 7, and 8. We need all the numbers even if it it zero.

[JustMike]

The inconsistencies are I think, due to different tubes I'm trying.

So here's what I have, measured at the tube sockets;

v1 pin1-368v
 pin 2-0v
 pin 3-1v
 pin 6-383v
 pin 7-0v
 pin 8-0v

v2 pin 1-264
 pin 2-0
 pin 3-0v
 pin 6-393v
 pin 7-265v
 pin 8-263v

v3 pin 1-403v
 pin 2-3v
 pin 3-4v
 pin 6-423v
 pin 7-4v
 pin 8-4v

 Could it be that I might have some bad tubes? I've got a pile of GT's, JJ's, Sovteks, Fenders, Genelec, unknown Chinese etc...

[sluckey]

V1-8 should not be zero.
V2-3 should not be zero.
V3 all pins are wrong.

What make and model is your voltmeter?

Put 3 known good 12AX7s in the little sockets and don't change them. Plug in known good output tubes also. Post one more set of voltage readings.

[JustMike]

New tubes;

v1
1-295
2-0
3-2.4
6-286
7-0
8-1.8

v2
1-244
2-0
3-0
6-370
7-243
8-243

v3
1-292
2-23
3-36
6-288
7-25
8-36

Played thru the amp and it sounds good so far! I gotta go thru my tubes So I guess the easiest way to check my tubes is to just put them in v1 and listen? Now that the amp works. This was frustrating as all. It's like changing spark plugs and cleaning the carb when all I had was some bad gas...
Thanks again, I couldn't have done it without you guys.

[sluckey]

Voltages look much better. Except for V2-3. If that is really zero volts then you still have a problem. I would expect approx 1v, maybe a little less. But not zero.

What make and model voltmeter do you have?

[JustMike]

v2-3 is .75 volts. I didn't change the scale from 1Kv when I checked the last time. My Cen-Tech P37772 is a Chinese Fluke copy.

[sluckey]

All voltages now look good.

[JustMike]

Amp has been working properly and sounding good. Thanks again for the help! So now it's time to start tweaking. I decided to convert it to plexi specs following a Ceriatone layout and have done so successfully. I plugged it into an attenuator, cranked the volume all the way and noticed some redplating. I\ve heard that this isn't uncommon when using resistive attenuators. I decided to check my bias voltage and it's way low. I can only get 13mv with the trim pot cranked. Bias ckt is 47k r and a 50k pot. What can be causing this? I'm not sure where the bias voltage is derived from, so it's time for another lesson.
Thanks Again!

[sluckey]

I can only get 13mv with the trim pot cranked.

Where are you measuring that 13mV?

What is the voltage on pin 5 of the output tubes?

[JustMike]

13mv is between pin 1 & 1 ohm r to gnd. Voltage on pin 5 is -29vdc.

[JustMike]

 Put some known good tubes in and my readings are 37 & 14 mv. Pin 5 on both tubes is -34.8v. These tubes are noticeably louder than the Mullards (reissues) that were in it. I've learned that a few mv won't matter much, but this is double. A bit much, eh?

[sluckey]

Put some known good tubes in and my readings are 37 & 14 mv. Pin 5 on both tubes is -34.8v. These tubes are noticeably louder than the Mullards (reissues) that were in it. I've learned that a few mv won't matter much, but this is double. A bit much, eh?

I like for my tubes to match better than that. I'd crack the glass on that 14mv tube.

[JustMike]

 I bought some brand new Mesa EL34's and put them in. Couldn't get the bias above 22mv or so and the amp sounds bad. Very low output.
 I put in some older Marshall EL34's(Chinese, I think) that came stock with a newer DSL40c and the amp is loud.
 What gives?

[JustMike]

 So I've been chugging along trying to get this thing right and last night I made a mistake. I just want someone here to tell me how bad it was. I was measuring voltage on pin 3 and my probe slipped and shorted pins 3&2. I saw an arc between the pins...not a spark, but an arc that lasted maybe a half second. Then my B+ was gone. I powered down and pulled the tubes and checked voltages again. I have heater voltage and 680ish coming out of the xfmr. My OT primary reads 82ohms.
 I'm thinking I might have taken one of the tubes out? How do I troubleshoot this?

[JustMike]

Problem solved! Nobody asked me to check the heater voltage. I miswired the heater secondary and instead of grounding the ct, I had one side grounded. 3.6vac "kind of" works...but now this amp sounds like a Marshall.

NOW. Back to the original problem of making the rocker switch light work!

[sluckey]

NOW. Back to the original problem of making the rocker switch light work!

So, reply #1 did not address that problem? Does your switch look like the switch in reply #1? Does the switch turn power on/off? Does the light never come on or is it on all the time?

It's possible that your scavenged switch is different from the old Marshall lighted switches. Can you show us close up pics of the front and back sides of the switch?