Shunt Reg voltages (fixed)

Listens2tubes · 23455

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Offline Listens2tubes

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on: April 05, 2014, 03:17:04 PM
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???
« Last Edit: June 07, 2014, 12:43:01 AM by Listens2tubes »

Neal P.

Offline Paul Birkeland

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Reply #1 on: April 06, 2014, 08:05:00 AM
Is this the OA/OB voltage on the regulator board?

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

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Listens2tubes

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Reply #2 on: April 06, 2014, 02:05:35 PM
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.

Neal P.

Offline Paul Birkeland

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Reply #3 on: April 07, 2014, 05:04:02 AM
Are you 100% sure that you have the 12BH7 and not the 6922 plugged into that socket? 


Paul "PB" Birkeland

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Offline Listens2tubes

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Reply #4 on: April 07, 2014, 01:34:41 PM
YES! I tried the EH and a Westinghouse. BTW the "lower" KREG actually measures 2 volts. My notes say "2V?"

Neal P.

Offline Paul Birkeland

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Reply #5 on: April 07, 2014, 06:49:11 PM
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?


Paul "PB" Birkeland

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Offline Listens2tubes

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Reply #6 on: April 08, 2014, 01:00:35 PM
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.

Neal P.

Offline Listens2tubes

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Reply #7 on: April 08, 2014, 01:23:49 PM
Pictures for your scrutiny.
« Last Edit: April 08, 2014, 01:25:22 PM by Listens2tubes »

Neal P.

Offline Paul Birkeland

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Reply #8 on: April 09, 2014, 06:43:31 AM
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).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Listens2tubes

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Reply #9 on: April 11, 2014, 01:13:29 PM
MJE5731AG are what's there.

Neal P.

Offline Doc B.

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Reply #10 on: April 11, 2014, 01:35:52 PM
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.

Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline Listens2tubes

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Reply #11 on: April 17, 2014, 01:47:58 PM
Yes, I just checked and they are LM431 chips. So they can be problematic?

Neal P.

Offline Listens2tubes

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Reply #12 on: May 10, 2014, 10:40:57 AM
Just ordered some Motorola MPS425 from Electronics Goldmine. Will report back after changing them.  :'(
« Last Edit: May 10, 2014, 06:00:13 PM by Listens2tubes »

Neal P.

Offline Paul Birkeland

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Reply #13 on: May 10, 2014, 11:19:24 AM
Quote from: Listens2tubes on May 10, 2014, 10:40:57 AM
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?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Listens2tubes

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Reply #14 on: May 10, 2014, 06:01:16 PM
I meant ordered so I corrected my post.

Neal P.

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