Speedball voltage, B+ low on the big board [resolved]

[[email protected]]

Hi. I have one voltage check outside of the target range  for the big board:

Targets from the manual:
OA  75-100V
OB  75-100V
G    0V
B+  170-195V

My voltage readings:
OA    90.7V
OB    77.4V
G      0V
B+    114.5V

B+ should be higher. It is probably the usual suspects (crappy joint somewhere), but I thought I'd ask where was likely.

Best,
Chris

 

[Paul Birkeland]

B+ connects back to terminals 2 and 4, as well as IA and IB on the big PC board.

How are the voltages on the small board?  Does B+ pop back up if you run the amp without the 6080?

 

[[email protected]]

Small board Measurements
OA 75V
IA 120V
B-A/B 0V
IB 120V
OB 75V

It did pass checks after mounting small board earlier

Large board without 6080 B+ is 225V

 

[[email protected]]

Also, perhaps the heat sink closer to the 6080 is hotter than the heat sink closer to the 12au7 socket. Not sure if this means anything.

 

[Paul Birkeland]

Are the TIP50 transistors properly mounted?  Be sure B+ to the big board is not connected to terminal 2 or 4 by accident.

If all else fails, you can post photos of the build and we might be able to spot something.

 

[[email protected]]

OK. My 15 y/o was sharp enough to point out that I was missing an LED on the big board at D2.... 

Once I put that in, it all seems to be measuring in range. On the big board OA, OB are measuring ~110V each. That is around 10% above the high - I am assuming that is OK - or is that just too high?

 

[Paul Birkeland]

Yes, that's OK.

 

[[email protected]]

Thank you, again - for being a patient and excellent guide. Great kit.