shunt regulator voltage is low [resolved]

[keithp]

I am testing the shunt regulator voltage before proceeding with the signal path wiring. One channel is perfect at 225 volts and the other one is only 95 volts. I switched 12BH7 tubes and get the same results. I am proceeding to dismantle the board and rewire. Any suggestions?

 

[Paul Birkeland]

One channel is perfect at 225 volts and the other one is only 95 volts.

You have a short at your socket, between D2 and D3 or D7 and D8.  This is grounding either D3 or D8 through one of the 220 Ohm resistors, which gives you ~100V instead of 225V.

-PB

 

[Paul Birkeland]

Hello Keith,

Just checking in to see if you've made any progress.

If this suggestion did not solve the problem, can you post these voltages:

IA
IB
OB
OA
Kreg A side
Kreg B side


-PB

 

[keithp]

Here is what I measured:

IA        292
OA      223

IB      291
OB    87

KREG A      5
KREG B      0



Thanks for your help
Keith

 

[Paul Birkeland]

KREG B      0

This is very indicative of a short between either pins 2 and 3 on the 12BH7 socket or pins 7 and 8.  (Sorry to sound like a broken record, but the voltages are strongly pointing to this)

It's also possible that the Kreg on the offending channel isn't connected to the correct pin on the 9 pin socket (should be 3 or 8).

It's also possible that the wire intended to go to Kreg is going to -reg.

-PB

 

[keithp]

I found a bad solder joint in the ground circuit on the shunt regulator board. Resoldering the joint seems to have fixed the problem as I am now getting ~220 volts on both of the red leads.