Tube Amp Archive

I want to thank everyone hanging out the Marshall forum here for your help - especially, Martin Manning! I went home and rewired the output jacks - its funny that I checked the wiring against the diagram but didn't bother to check the cliff jacks themselves as they were flipped around. Did I mention...

Awesome! I knew something was screwy there. I must have checked it against the diagram a dozen times and could not reconcile the differences with other diagrams from the web. I just assumed that the diagram was correct. Obviously, I still missed something. Going to wire it as yall suggested when I g...

I'm beginning to doubt the output jack wiring. I followed the diagram exactly.

Yes - well 428 but close

Thanks so much for this!

OK - I measured 39.9-40 ohms across both OT taps to the CT at the standby switch.

40 ohms x .041mA = 1.64vDC

is this correct?

I adjusted the bias pot and am getting 1.67-1.64vDC at both pin 3 connections now.

[IMG:280:186]http://imagizer.imageshack.us/v2/280x200q90/840/ivfy.jpg[/img]

[IMG:280:186]http://imagizer.imageshack.us/v2/280x200q90/850/okqd.jpg[/img]

[IMG:280:186]http://imagizer.imageshack.us/v2/280x200q90/841/twurk.jpg[/img]

I'm relatively new to this - would you be kind enough to explain exactly how to measure this? Most web articles I've found are not to the point.

Should I be seeing any voltage at pins 2 & 7 of V1 with no input source or audio signal present?

updated my last post with full voltage readings with tubes installed, in play

Pin voltages (in play) (all tubes installed)

V5 (EL34)
3: 420
4: 413
5: -36

V4 (EL34)
3: 426
4: 407
5: -36

V3
1: 227
2: 25.7
3: 42.5
6: 216
7: 27.8
8: 42.6

V2
1: 165
2: .4mV
3: 1.1
6: 295
7: 164.2
8: 165.5

V1
1: 192.2
2: 0
3: 1.5
6: 196.1
7: 0
8: 1.6

AC line voltage is 119vAC - checked this out first.

edit: I should have been testing that in DC. When I do this, I get 472vDC out of the rectifier and into the filter cap with the recto and PTs installed.

When taken out of standby, rectifier voltage drops to 421vDC

with the rectifier and EL34s in place, i'm getting 1000vAC plus coming out of the rectifier. this can't be right.

Pin voltages (in standby)

V5 (EL34)
3: 3.5vDC
5: -36.5vDC

V4 (EL34)
3: 3.5vDC
5: -36.6vDC

V3
1: 3.5vDC
6: 3.5vDC

V2
1: 3.4vDC
6: 3.5vDC
7: 3.4vDC

V1
1: 3.4vDC
6: 3.4vDC

The voltage threw me off too but I can't figure out where that would be coming from.

Thanks for your help - I had all the tubes out when I did this earlier. I will power it up when I get home and post voltage readings at the pins while the tubes are out.