Newbie looking for some diagnostic help (Solved)

[elawyoung]

I just recently attempted to build the Stereomour 2A3.

At the end all resistance checks were good.  My problem is on the DC voltage checks.  Below is a summary of my readings.  Any help with a diagnosis would be greatly appreciated.  All 3 tubes filaments began to glow after a few seconds.  One symptom I noticed was the 5W 4K7 and 10W 1K6 resistors on the A side were getting really hot, so much so that the black lettering turned brown and started to fade.

AC Check with the manual values in ()
A1/A4 2.52 V  (2.5 V)
C1/C4 2.53 V  (2.5 V)

DC Check with the manual values in ()
HV+ A side 372 V  (380 V)
HV+ C side 410 V  (380 V)     Out of Range

Terminal
1  280  (350 V)     Out of Range
2  215  (165-220 V)
3  0  (0 V)
4  0  (0 V)
5  162  (60 V)     Out of Range
6  0  (0 V)
7  0  (0 V)
8  0  (0 V)
9  0  (0 V)
10  0  (0 V)
11  0  (60 V)
12  -.5  (0 V)     Out of Range
13  0  (0 V)
14  198  (165-220 V)     
15  410  (350 V)     Out of Range
16  161  (60 V)     Out of Range
17  372  (380 V)
18  0  (0 V)
19  410  (380 V)     Out of Range
20  0  (60 V)     Out of Range

A1  162 (60 V)      Out of Range
A2  278 (350 V)     Out of Range
A3  ~0 (close to 0)
A4  162 (60 V)     Out of Range
C1  0  (60 V)     Out of Range
C2  410 (350 V)     Out of Range
C3  ~0 (close to 0)   
C4  0  (60 V)     Out of Range

IA  410  (380 V)     Out of Range
IB  372  (380 V)
OA  216  (165-220 V)
OB  198  (165-220 V)
Kreg A side  2.48  (2.5 V)
Kreg C side  2.48  (2.5 V)
-reg A side  0  (0 V)
-reg C side  0  (0 V)

Thanks for all the help.

[Paul Birkeland]

Neither of your output sections are drawing proper current.

The C side is particularly disturbing, do any lugs of the hum pot touch the chassis plate?

Can you post some photos of your build? 

Don't run the amp for more than 10-30 seconds when rechecking voltages, you have a short through the high voltage supply that is going to do some damage if left running for very long.

-PB

[elawyoung]

I can post some photos later this evening, are there any specific angles or connections that would be most useful to see?

-EY

[elawyoung]

I've attached some photos of the build.  I'm a little nervous I may have done some damage.  I powered the amp for about 5 minutes during the initial testing.  I went back over all the connections this evening and found that the wire connection from B9 of the nine pin connector to terminal 8L was not soldered on the B9 side.  I'm not sure what this would have done.  Everything else looked okay to me.  None of the hum pot lugs were touching the chassis.  After correcting B9 I quickly re-tested, but got the same results.  I also noticed that the 5W 4K7 and 10W 1K6 resistors overheat very quickly.  I only powered up once for the quick re-test for about 10 seconds and the resistors were very hot.

[elawyoung]

Photo

[elawyoung]

Photo

[elawyoung]

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[elawyoung]

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[elawyoung]

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[elawyoung]

Photo

[Paul Birkeland]

Will you run the amp without the 2A3's, then report the following voltages:

IA/IB on both sides of the PCB
A2 and C2
A1 and C1

-PB

[elawyoung]

Results without the 2A3's.

IA 441 V
IB 441 V
A2 441 V
C2 441 V
A1 0 V
C1 0 V

-EY

[Paul Birkeland]

Where does the red choke wire on the A side land?  I would wonder if it is somehow shorting to the 1K6 and 4K7 resistors.

-PB

[elawyoung]

Choke wire was clean into 17L. So I decided to do one more close inspection, especially underneath the PCB. I noticed that pins B7, B8, and B9 were very close together. I think maybe B8 and B9 solder joints were touching. I got in there and spaced them out... All voltage checks were clean.  I think when I mounted the PCB and positioned the connection from B8 to the PCB I torqued the pin toward B9.

Now I'm ready to make sure they stay clear, and move onto the hum balance and some tunes.

Thanks so much for your help and quick responses.  I can't wait to get on some music.

[Paul Birkeland]

Did that clear up your voltages? It wouldn't be impossible, but seems unlikely.