HUM! Need some help...

[danman]

To check the coupling caps, set your meter to the highest DC voltage scale and check for DC voltage at both ends of the caps. If the cap is healthy you will only read DC voltage on one side and none on the other. The coupling caps job is to block DC but allow AC to pass through. If you read DC voltage on both sides of the cap then it is defective.

[MHProd]

So, with the recto and power tubes in I have 425V on the PI side (no tubes in). On the other side of the caps, I get -48V.
Should take some measurements without the power tubes but with the preamp tubes installed?

[danman]

That sounds correct. The negative voltage on one side of the cap is the bias voltage. If the cap was bad you would be seeing the higher number on both sides which would upset the bias to the power tubes.

[MHProd]

So, without the power tubes I get the following:

B+ 470V measured at the mains 32uF where the OT CT and one side of the choke are:

V1:
1. 229
3. 1.8
6. 233
8. 1.8

V2:
1. 189
6. 340
7. 189
8. 191

V3:
1. 259
3. 44
6. 253
8. 44

Looks within specs I believe.

So,I guess something is definitely wrong in the communication between the power amp and the PI.

[MHProd]

The choke measures 108 Ohms.

With the preamp tubes only. I get 470V on both sides of the choke.

With only the KT66 in biased at 37ma, I get 435V on both sides.

Where else should I look?

[neikeel]

Your voltages look ok.

It will almost certainly be something silly and embarrassing that you cannot see because you have looked at it so much and as such you must post some pictures of the board and the PI in and out wiring if you want us to help

We have all been there

[MHProd]

Fixed it!

I originally built the amp with the PPIMV. Somehow I must have wired the OT primaries backward. After removing the PPIMV, I rewired the leads to Pin5 in the right order which resulted in the hum/fuses blowing fiasco. Swapped them around and everything is fine now!

Still have to open a photobucket account though...

[danman]

Glad you got it fixed!