Mainline Resistance Check

[bdog9]

OK. Check resistance as suggested and range form 25 to 0 noted, so moved to voltage test. When I switched on the power the tubes did not glow and I turned it off. I could smell heat and on careful inspection the green resister on the power board had one leg with bubbling solder.
It has cooled now.  Advice?

[Paul Birkeland]

Remove the red wire leaving the +275V pad and power up the amp again, measuring what's available on the +275V pad if you don't get the hot smell again.

If the resistor continues to get hot under these conditions, then you have a backwards 100uF/450V cap or you have swapped two of the caps on the power supply board on accident.

[bdog9]

Cleared both red wires from 275 connection, powered up and no smoke and 365 volts between 275 + and ground.

[Paul Birkeland]

When you put back one of the two red wires, you'll get that issue again, and that can be used to narrow down which half of the amp is misbehaving.  It's also possible that either wire causes the same problem, in which case you've just made the same mistake on both channels.

[bdog9]

Thanks for your help ! Back to the build.

[bdog9]

Reporting back. Stepped away a day or two and came back to reinspect all connections. On removing the two C4S boards I embarrassingly found the black wire going from inboard bA to inboard bB going instead to a lead just to the inside of the transistor  on both boards. The lead is on the inside of the transistors but in a direct line with IA.
I unsoldered them both cut new wires and positioned them properly.
I continued to inspect and found a few solder joints that I cleaned up.
I rechecked the resistance and all was good.
Inspired I installed the tubes and they did not light up in spite of a good fuse.
I rechecked my voltage at 275 and got no reading. Disconnected red wires at 275 and still no reading.

[Paul Birkeland]

Are you certain the fuse is in the correct half of the fuse holder?

[bdog9]

yes .

[bdog9]

I have power to the transformer from the switch. No power at the +125v lead, either one.

[bdog9]

OK. Went back to the manual and ran all voltage tests as described. All were successful. Redid my resistance checks and all were good. Stopping for the evening

[bdog9]

Removed the red leads to the power board and tested from +275DCV both links to ground and got nothing.

[Paul Birkeland]

Your last two posts are somewhat contradictory.  If you passed all your voltage checks, then you have to have the correct DC voltages coming out of the power supply board.

[bdog9]

Sorry, I just retested using method on pg 49 and also the method you recommended in the the forum and did both get 361-389 vdc.  My mistake.

[bdog9]

Checked resistance again, All check ok but some that should be o ohms are 1 ohm, I used the harbor fright dmm for these measurements, It did not want to measure high volt dc so I switched dmm to the Klein which worked well. I think this was this mornings problem. In any case I installed the tubes powered up and they lit up. Voltages varied from what they were supposed to be. +275vDC 302V  +6.3vDC  59  -6.3vDC  52.8. The wording on the next measurements is confusing to me. The IA on one board was 302 on the other it was 301. I did not recognize an IA on the B side but measured Ib and got 215 one the first board and 300.5 on Ib on the second. The Breg was 215 and 300 The -reg was 215 and 300 and the Kreg was 2.7 and 300. I think something is wrong ?

[Paul Birkeland]

You have 300V on a Kreg terminal?