0A2 regulator tubes

OK, I corrected the wiring on the 6SN7s...and I fired it up.

The 0A2s still did not light up.

The voltages I got were:

C1: 466
C3: 412
OA2s: 314
C4: 217

This was with about 110 AC in.
Then I tried with closer to 117-120 in. Still no OA2 action, and these were my readings:

C1: 505
C3: 440
OA2s: 325
C4: 225

Any ideas how to proceed?
 
One last thing - I just tested the 0A2s...I bought them as NOS from an online vendor. They both light up in the tester, but read "replace". Could that be the problem? Unfortunately I don't have any others to test in the circuit.
 
The voltages at 110VAC in look ok, are you sure they aren't on? They don't get very bright like other big glow tubes. Try putting a 10 ohm resistor at the very bottom of the 0A2 chain and put a voltmeter across it, checking to see if any current is flowing.

Aside from that, try leaving the 6SN7 filaments off for a few seconds after turning on the B+, then once the 0A2s turn on (hopefully), turn on the 6SN7 filaments.
 
They are definitely not lighting, as they light in my tester so I have seen them light. Also, the voltages coming out of them is exactly the same as going in.
 
Would it hurt anything to power it with the 6SN7s pulled, just to see if the 0A2s light? Or do i need to put a switch on the filaments for the test?
 
Nevermind, I quickly wired a switch.

So with the 6SN7 heaters off, the 0A2s actually started to sporadically light, though they never changed the voltage passing through them at all. It was about 350v, give or take. Once I switched the 6SN7s back on, the 0A2s stopped firing and the voltage went back down to about 317.
 
A few questions so we can narrow things down...

1) how much current is each 6SN7 stage drawing?

2) what's the resistance of the HV secondary on the PT?

3) what's the resistance of the choke?

just so my psud simulations are correct...:D
 
Something still doesn't seem right with the load. Attached is the psud sim with the resistances and values you gave. The program is usually spot on with all the ESRs correct. I'm not sure if you meant each half of the PT was 88 ohms, or the whole secondary was 88 ohms, so I err'd on the side of closeness to your voltages, but it still isn't agreeing with a 40mA load. It'll be even farther away with 44ohms/half.

But anyway, the with the voltages you gave, it's no surprise the VR tubes aren't lighting. The pair will need more than 317V across them to light. Something either at the load or somewhere else is goofy.
 

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It was 88.3 across the whole secondary - 44 across each half. I just measured again and got about the same thing. Any idea what could be going wrong? Could it also be that the 0A2s are faulty? Could I have baked them when sending too much current across them initially? Should I try a different pair of 6SN7s, that were not in when I had their wiring incorrect?
 
currituckco said:
It was 88.3 across the whole secondary - 44 across each half. I just measured again and got about the same thing. Any idea what could be going wrong? Could it also be that the 0A2s are faulty? Could I have baked them when sending too much current across them initially? Should I try a different pair of 6SN7s, that were not in when I had their wiring incorrect?
Click to expand...

There should be more than than 317V across them if they are not firing. According to psud, if the VRs are not ON and there is 317V across them, then the load is drawing 62mA, more than the 40mA it should be drawing. Double check the 6SN7 wiring again and try different tubes to be sure.
 
Wait - 40mA is what they were drawing, without the 0A2's firing. I measured that. I have no idea what they SHOULD be drawing. I'll double check the 6SN7s. The 0A2s also were only sporadically firing with 350v and no 6SN7 heaters, and they were not regulating the voltage. Does this tell us anything?
 
currituckco said:
Wait - 40mA is what they were drawing, without the 0A2's firing. I measured that. I have no idea what they SHOULD be drawing. I'll double check the 6SN7s. The 0A2s also were only sporadically firing with 350v and no 6SN7 heaters, and they were not regulating the voltage. Does this tell us anything?
Click to expand...

With a 40mA draw, the voltage across the VR tubes (without them firing) should be about 400V, so something is goofy with it being 317V. Maybe a bad 'lytic capacitor somewhere? Maybe a resistor isn't correct?
 
Hmmm...I just checked the 6SN7s and tried a different pair and everything was the same, except that even with the 6SN7 heaters off and 350v across the VRs they didn't fire, didn't even sputter like they did before.

It's possible a 'lytic is bad, but they were all new when i put them in. The only one that has been appreciably stressed is C1, as it's been getting close to 500v, sometimes more, across it every time I turn this thing on, though it's never stayed on for more than like 1-2 minutes. Where could there be a wrong resistor or bad cap? I'm 99% sure the 6SN7 wiring is right now (there's always a possibility I missed something) and same with the power supply. There's literally 3 resistors in this part of the power supply, how wrong could I have gone? I'm pretty positive those are right, other than the 2k (R4) being a 13W not 15W because I couldn't find a proper 15W at that value.
 
currituckco said:
OK, I corrected the wiring on the 6SN7s...and I fired it up.

...

Then I tried with closer to 117-120 in. Still no OA2 action, and these were my readings:

C1: 505
C3: 440
OA2s: 325
C4: 225
Click to expand...

From this, it looks like (440-325)/2000 = 57.5mA is flowing into the node with the 0A2s from the 2k resistor, yet (325-225)/2400 = 42mA is flowing into the 6SN7s, so 15.5mA is going somewhere :scratch2: Measure the current going through the VR tubes with that 10-ohm resistor method. Maybe they have gas (other than the intended type) in them. - could be why the tester said replace.
 
I didn't quite understand where I'm supposed to put the 10 om resistor and where I'm supposed to measure...Does the resistor go from where the 2nd VR goes to ground, and then the other end of the resistor to ground, and I measure across the resistor? And by the way, thanks for the tons of time and energy you're putting into this with me. You're a class act, bricktop!
 
currituckco said:
I didn't quite understand where I'm supposed to put the 10 om resistor and where I'm supposed to measure...Does the resistor go from where the 2nd VR goes to ground, and then the other end of the resistor to ground, and I measure across the resistor? And by the way, thanks for the tons of time and energy you're putting into this with me. You're a class act, bricktop!
Click to expand...

Yup, connect one end of the 10-ohm resistor to pins 2,4,7 of the bottom VR tube, and the other end to ground :thmbsp:. No problem!
 
Oh yeah, that's another thing that confused me - are 2,4,7 all tied together internally such that I can treat one pin as all three, or do I need to tie all three together externally, or what? I figured they were tied together internally, because I get 0 ohms between the pins...
 
currituckco said:
Oh yeah, that's another thing that confused me - are 2,4,7 all tied together internally such that I can treat one pin as all three, or do I need to tie all three together externally, or what? I figured they were tied together internally, because I get 0 ohms between the pins...
Click to expand...

Yup they should all be connected internally. You could use just one of them as well.
 
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