Mainline Resistance Check

[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?

 

[bdog9]

I did. But now I do not. Solder joint had broken loose.After it was repaired everything sorted out on its own.Both sided biased to 145. Could not have done it without your help. Next time your in Fort Worth call me and I will make a steak dinner. Bill

 

[Paul Birkeland]

I do get to Texas from time to time... 

One thing I would recommend in your instance is to plug in some cheap headphones and play music through your amp, then give the top panel a few hard whacks with your hand.  If the music keeps playing uninterrupted, then it's rather unlikely that there are any other issues that may pop up.  If the music drops or pops, then you may need to poke around a bit more to look for other loose/broken stuff.