Shunt regulator voltage problem

[Mid-Ranger]

I checked the voltage with the 12BH7 installed, all LEDs light up and the tube glows, but the voltage goes from over 300 and then drops to 100......

Any thoughts on what this could be or what I should look for?

 

[Paul Birkeland]

What do you see on each Kreg?  Can you post some photos of the board and its connections?

-PB

 

[Mid-Ranger]

I get 4 for each kreg.... let me see if I can get some pics.

 

[Mid-Ranger]

Pic

 

[Mid-Ranger]

So can I go on with some of the rest of the build?

I hate to stop all progress.....

 

[Mid-Ranger]

Ok like a noobie I forgot to check the other leg, so the wire from D7 measures 222v, it's the wire from D1 that drops to 100v.

 

[Paul Birkeland]

Ok like a noobie I forgot to check the other leg, so the wire from D7 measures 222v, it's the wire from D1 that drops to 100v.

D7 should be grounded to the board through a 220 Ohm resistor.  If D7 has appreciable voltage on it (more than 1V), either the resistor is broken, or there is a wiring error.

Do not proceed with the rest of the build until the regulated power supply is functioning.

-PB

 

[Mid-Ranger]

Hi,

Sorry not D7, I meant the red wire from D6 has the proper voltage.

 

[Mid-Ranger]

Could the tube be an issue?

Half of it not working?

 

[Paul Birkeland]

Can you confirm that you have a 431 regulator on each side of the board and not an MPS4250A installed by accident.

-PB

 

[Mid-Ranger]

Yep, 431 on both ends.

 

[Paul Birkeland]

And 2N2907's in the middle? (not 2N2222's)

 

[Mid-Ranger]

Yes, took me a while to finally be able to see the writing on the A side, but both are 2907.

 

[Mid-Ranger]

Paul I have checked every single part on the shunt regulator board and confirmed them all.

Also went over the wiring for every tube pin on D socket.

I am attaching a closer pic of IB and I0.......could a solder bridge cause the voltage drop problem?

Charles

 

[Paul Birkeland]

I am attaching a closer pic of IB and I0.......could a solder bridge cause the voltage drop problem?

I don't see a solder bridge between IB and OB, so no issues there.

Can you snap some photos of the bottom of the board?

Also, can you carefully measure the voltage on each side of the 2.49K resistor on the offending side?

-PB

 

[Mid-Ranger]

Getting a low reading on the 431 regulator on the side in question......could that be it?

 

[Paul Birkeland]

What's the reading you see?

 

[Mid-Ranger]

The 2 outer legs show .825 resistance the middle leg measures .001

 

[Mid-Ranger]

Just checked the other 431 and it measures differently.

I'm checking resistance with it still soldered in the board, should I remove it to check it properly?

And could a bad LM431 cause low voltage on one side?

 

[Paul Birkeland]

Please check the voltage on each side of each 2.49K resistor.

Measuring resistance across a semiconductor won't really tell you anything unless it's completely shorted.

-PB