Shunt Reg voltages (fixed)

[Listens2tubes]

Doing the voltage test I am getting ramp up to 340VDC then drops to 75volts both sides. Tried a vintage tube with similar results. Changed the battery in my CTech digital meter and brought out the VIZ (RCA) solid state analog meter. What do you think I did wrong???

 

[Paul Birkeland]

Is this the OA/OB voltage on the regulator board?

How is your IO/IA voltage?
How about Kreg on both sides?

 

[Listens2tubes]

OA/OB 51/45,  IB/IA 281/284,  KREG 48/42? not sure from my notes about the 42V on the lower KREG. Could not locate IO.

 

[Paul Birkeland]

Are you 100% sure that you have the 12BH7 and not the 6922 plugged into that socket? 

 

[Listens2tubes]

YES! I tried the EH and a Westinghouse. BTW the "lower" KREG actually measures 2 volts. My notes say "2V?"

 

[Paul Birkeland]

Is there any way you can post photos of your board?

Can you confirm that the 220 Ohm carbon composition resistors are in place at tube socket pins 2 and 7?

 

[Listens2tubes]

Actually I checked the 220 ohm caps at the same time. I looked at their leads to be sure they were not touching anything under there. I'll post a picture soon.

 

[Listens2tubes]

Pictures for your scrutiny.

 

[Paul Birkeland]

Can you confirm that you have 431 regulators in the 431 position?  Your high voltage at Kreg would be consistent with having an MPS4250 in there instead (don't ask me how I know).

 

[Listens2tubes]

MJE5731AG are what's there.

 

[Doc B]

The MJE5731As are the big transistors with the heat sinks. PB is asking about the smaller black TO-92 style plastic devices that do not have heat sinks.

 

[Listens2tubes]

Yes, I just checked and they are LM431 chips. So they can be problematic?

 

[Listens2tubes]

Just ordered some Motorola MPS425 from Electronics Goldmine. Will report back after changing them.  :'(

 

[Paul Birkeland]

Just order some Motorola MPS425 from Electronics Goldmine. Will report back after changing them.  :'(

Does this mean you had an MPS4250 in the position for the 431 regulator?

 

[Listens2tubes]

I meant ordered so I corrected my post.

 

[Listens2tubes]

Dang! This turned out to be simpler than I thought it would be. On disassembly I noticed I had the 220 ohm resistor from D7 soldered to the front right Kreg (see second photo) instead of the rear left bA. Once corrected and double checked for wiring and shorting errors I have 223VDC stable at rest on both sides. HAPPY DAY!!!