Failed voltage check, some LEDs not lighting up, tube no longer lighting up

[Shackney1127]

Resistance checks passed. A side LEDs of shunt regulator board no longer light up. Tube B doesn't light up. Here are my voltage readings:
1A: 218v
1B: 255v
OA: 164v
OB: 146v
OC: 96 V
OD: 141 v
OkA: 95 v
OkB: 138 v
OkC: 1.7 mv
OkD : 0.98 v

I can supply pictures if needed.

Thanks,
Stephen

 

[Paul Birkeland]

If the tubes don't light up, nothing in the high DC voltage section and C4S board is going to work properly.

The tubes glow from the shielded twisted pairs of wire that feed pins 4/5 on the front two sockets and pins 4/5/9 on the D socket.  I'm guessing by your voltages that the 12AU7 is still glowing, are the rest dark?

 

[Shackney1127]

Only the left EF86 tube isn't lighting up. I'll check the wiring when I get home. It lit up before, so I'm not sure what could have happened.

 

[Shackney1127]

One of the issues might be one of the tubes. I examined the wiring and found nothing wrong. I decided to switch the EF86s around. Sure enough, one tube lights up regardless of which socket I put it in, and the other doesn't. Both always get warm, so that tells me both sockets are getting power, right?

 

[Paul Birkeland]

Yes, you may have a tube with pins that need a tiny bit of extra cleaning.  This doesn't necessarily indicate a bad EF86.

 

[Shackney1127]

Cleaned both the pins. Same result. You can't even see it lit up in this picture. One lights up at the very bottom, the other not at all. Both get warm.

 

[Shackney1127]

Some other pictures.

 

[Doc B]

See how the top of the left EF86 is white instead of silver? Left EF86 is cracked and the getter is shot. Replace it.

 

[Shackney1127]

Replaced the offending tube. Readings are as follows:
1A - 239v,
1B, 279 v
Oa, 161 v
OB 163 v
OC 95 V
OD 94 V
OKA: 94 V
OKB: 94 V
OKC: 0.95v
OkD: 0 85v

 

[Shackney1127]

All tubes now glow.

 

[Paul Birkeland]

Now you will need to do some investigating regarding why the regulator board above the 12AU7 socket is no longer working.  Can you post the IA, IB, OA, OB, KregA, and KregB voltages on that board?

 

[Shackney1127]

Readings are as follows:

1A: 286v
1B: 286v
OA: 283v
OB: 238V
KregA: 1.2 v
KregB: 8v

 

[Paul Birkeland]

Well there are issues on both sides of the C4S regulator board above the D socket, as one side has enough regulator voltage to work and the other side seems to be saturated and not regulating.  Weird results like this are something I've run into when I have swapped wires leaving that board going to the tube socket (swapping the Kreg leads would likely cause this exact issue).

 

[Shackney1127]

Unscrewed thldere board. The white wire attached to C8 had been knocked out. I resoldered it. Powered it on. The LEDs on the A side of the board turned on, so I started to do voltage checks only to notice the LEDs had cut back off. Here are pictures.

 

[Shackney1127]

Any advice? Thinking of completely replacing the wire pictured. Do I just need to send it in to fix my mistakes? Just want to know what my forward path is with this project.

Thanks,
Stephen

 

[Doc B]

It is possible that a wire has been nicked when the insulation was stripped and the nick turn into a break as the wire was worked. These will sometimes be under the insulation where they can't be seen and often cause intermittent behavior.

 

[Paul Birkeland]

I would send this in for repair. You can contact queen(at)bottlehead(dot)com and let her know that we have been working on this on the forum and I let you know you could send your kit in for repairs.