No sound from 18 watt TMB

[lpresnall]

I really really don't want to try to lift the board at this point!

[mark enger]

ya till you get contuinity all down your powerrail

[lpresnall]

Did you forget the blue dotted line next to the 22uf-450 cap?

I don't think so, but I'm gonna check everything underboard this evening. Will report back. Thanks again!

[lpresnall]

Another re-check and connecting the points that should be underboard wiring with wire on top of the board has wrought thus:

PIN 1 2 3 4 5 6 7 8 9
V1 101.3 0 .65 0---------0 86.5 -.53 0 0
V2 139.2 35.8 53.4 0---------0 142.4 35.9 53.4 0
V3 103.2 -.38 .53 0---------0 177.5 103.1 103.4 0
V4 .59 2.3* 28.5 0 0 .74 242.7 1.10* 225.5
V5 .007 3.3* 28.5 0 0 .006 244.6 .005 225.4
REC 285.5 285.5

CAN CAP CAN CAP 16uF 22uF
278 228 186 177

* This is the beginning voltage, then it drops steadily while I have the probe on the pin.

The amp is clearer and louder now, but still seems hot and I'm a ways off (to the low side) on several voltages. This is hard for me to accept and I'll have to sort it out to find peace.

[mark enger]

Is it possible the pt is hooked up wrong, i assume its multi-voltage, one thing you could try is pulling the ez81 and putting the diodes back in, this will raise your voltage 20-30v
also only measure pins 2,3,7,9 for DC on valves 4 and 5 the powetubes
IM LOOKING AT YOUR PIX LOOK AT THE SCREW IN THE BOARD FOR THE STANDOFF IS IT HITTING THE TURRET GOING TO PIN8 OF VALVE 1? if it touching and pin 8 isnt getting resistance its gonna screw stuff up

[mark enger]

here pull that screw right out

[mark enger]

and check the resistor that goes to pin3 of the powertube the cathiode is it touching a standoff screw as well

[lpresnall]

Mark, it was touching the screw! Here are the latest values:

PIN 1 2 3 4 5 6 7 8 9
V1 196.7 .007 .65 0---------0 138.4 -.009 .96 0
V2 197.8 51.9 76.4 0---------0 200.9 52.5 76.4 0
V3 139.8 -.123 .90 0---------0 252.5 139.7 140.2 0
V4 .30 .027* 10.7 0 0 .42* 339 .637* 323.7
V5 .002 .026 10.7 0 0 .002 338 .035* 322.5
REC 301.5 301.5

CAN CAP CAN CAP 16uF 22uF
351 324 265 252

* This is the beginning voltage, then it drops steadily while I have the probe on the pin.

[lpresnall]

That V1 Pin one is a typo...should be 146.7.

So it seems I'm running high on everything now.

[mark enger]

everythings looking better is it sounding better?

[mark enger]

If voltages are dropping while testing, thats a weak ground,

[lpresnall]

Yep, it's sounding pretty good although the last marshall I played thru was in 1982 so my memory might be clouded! As far as the ground, I've looked everywhere for the "right" pllace/way to ground and all the info I found is conflicting. I think Tube Depot has an 18 watt plan with a ground lug at a board standoff, but I'm unclear as to what goes there. Is the buss bar attached to it to ground the pots?

[mark enger]

is she humming at all? I always ground the buss right below or at inputs with a seperate ground lug , seperating powersupply grounding from pre-amp and phase invert grounding, but if it not noisey dont change anything

[lpresnall]

Well, there's some...don't know if I'd call it hum or hiss but it could be quieter. I was just so busy doing the happy dance around the shop over having something that resembled an amp...so I should come off the input jack ground to the buss bar and from the bar to the chassis?

[mark enger]

yep, disconnect the buss from ground over by the power transformer
add a ground lug by the inputs and ground buss to it, grind a kinda ruff area
in chassis where you bolt the lug, These amps are somewhat noisey but you can get them quiet, looks like you need to tidy up your wiring almost all your wires to the socket are a bit long, this is something you can work on later