Mesa Mark IIb - need help restoring amp

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bluelair

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Purchased a fuse-blowing Mark IIb on Facebook about 2 years ago. Quickly determined it had a blown power transformer.

Here's how it looked before:

f4q7ksA.jpg


5vdLwDw.jpg


ZDERdHt.jpg


Since Mesa doesn't sell the PTs any longer, I went with this one which had the closest specs. http://www.classictone.net/40-18042.pdf

Replaced the caps and tubes as well with new Mesa caps and JJ tubes.

Here's how it looks now:
8yHcl3k.jpg


The new Classictone PT has a lot more options than the original one. I went with the 690v high voltage option, which I wired to the original power supply board. I wired it with the 2 red-white wires and the 1 red-yellow CT wire to the PS board. Also wired the two green leads to the heater pins of the nearest tube socket.

Powered it up with a a variac to take some readings. Sound is very scratchy, I have to put a strong input signal in to get any sound at all. Pots are quiet.

The weird thing is that when I power the amp down, by backing down the variac, there are two distinct points where the amp wakes up and sounds awesome as the voltage drains down to zero. The amp sounds like it probably should, however it ONLY does that while descending the voltage, there's no way to hold it.

Here's the schematic:
4137.gif


I tried both patching the send-return jacks on the back, and also plugging a guitar directly into the return port, got the same sound results.

Took some voltage readings,
"A" was 440-441v (Spec: 445v)
"B" was 440v (Spec: 444v)
"C was 422v (Spec: 433v)
"D" was 416v (Spec: 425v)
"E" was -61v (Spec: -52v)
"F" isn't there, seems to be for the EQ, which I don't have.

Next I tested the AC voltage of the heater wires (green) that are connected to the tube pins. They all consistently tested around 3.8-3.9v AC, the further away I got it dropped down to 3.6-3.7.

I'm still struggling to decipher the schematic vs. the actual layout to test the tubes. I *think* I have it right,

V1 is the first 12AX7, closest to the input jack (V1A and V1B are the same tube, just different pins), upper right in the photos above.

Then V2 and V3 are in line, next to it.

I don't have Reverb so no V4. And V5 is on the other board to the left to the 6L6s.

The below is what I got from the tube pin readings to compare against what was on the schematic.

V1A Pin 1, 269v. (Schem says 266v)
V1A Pin 3, 2.14v. (Schem says 2v)

V1B Pin 6 140.4v (Schem: 130v)
V1B Pin 8 1v (Schem: 1v)

V2A pin 1 225.5v (Schem: 220v), Pin 3 - 1.37v (Schem: 1.2v)
V2B pin 6 253.8v (Schem: 250v), Pin 8 - 1.69v (Schem: 1.75v)

V3A pin 1 - none because I don't have Reverb.
V3B pin6 202.2v (Schem: 220v), Pin 8 2.29v (Schem: 2v)

V5A p3, p8: 87.1v (Schem: 80v)
6L6GC tubes, Pin 5: -74v (Schem: -51v)

Do these look OK?

What would you try next?
 
I'll suggest check point E voltage, the BIAS voltage seems not quite right.
Check those silver shell caps and the resistors for BIAS voltage.
 
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