EF86 tubes not lighting up

[Aural Robert]

I finally got around to getting this project finished. It's been a while since I assembled it so I went through the manual and rechecked all my wiring and connections, checked my resistances and all appears ok.

Plug it in and power up, all the LEDs on the underside light up, the 2 middle tubes light up, but the outermost EF86's do not. I didn't try to take any voltage measurements, just shut it down and came here for advice. ??? Where do I look first?

Aural Robert
... Oh what fun it is ...

 

[Adrian]

Be sure to look real close, under darkened conditions, at the EF86s.  The heaters can be hard to see behind the shields.

 

[Doc B]

The very first thing that popped into my head was "why didn't he take voltage measurements?" 

 

[Aural Robert]

I got a few minutes yesterday to power up and check my voltages. The B side is almost spot on, but on the A side the following do NOT check out:

Kreg (should be 1VDC) reads 0.3mv (this is the same on the B side)
OB (should be 100VDC) reads 58
breg (should be 100VDC) reads 55.8
OA (should be 170VDC) reads 0

I also checked the source points for these and got identical readings. I swapped the tubes and nothing changed. I checked all my solder points and resistances in this area and all is good. So, where to look next?

Aural Robert
... He's checking it twice ...

 

[Paul Birkeland]

Resolder the center leg of each MJE5731A.  The 0V on OA would indicate that no current is reaching the plate of the 6922, which could easily cause all the other issues you describe.

 

[Aural Robert]

Thanks Paul. I tried that and no change. I guess I could have a bad MJE5731A or I toasted one installing it.

I`ll ping the Queen for a couple of replacements.

 

[Paul Birkeland]

Thanks Paul. I tried that and no change. I guess I could have a bad MJE5731A or I toasted one installing it.

I`ll ping the Queen for a couple of replacements.

No, that would be a waste of your time.  Very few soldering irons are capable of destroying an MJE5731A, and it would take a significant amount of time for that to happen (several minutes of exposure with a very, very hot iron).

The other options for OA being 0V would be a miswire directing the voltage from OA to ground.  You can power up your Eros, let it sit for 2-3 minutes, then power it down and check that the B+ is under 12V.  Next, carefully check how hot the MJE5731A is that feeds the OA that is 0V.  If the MJE5731A is hot, then you have a short that's drawing that voltage down, which is generally an improperly placed jumper wire, or an improperly placed component.

 

[Aural Robert]

Are you going to be there on Saturday? I was thinking of coming down to the meet anyways so this gives me a great excuse.

Aural Robert
... 58 angels at my gate ...

 

[Paul Birkeland]

Sure, I'll be there, and I can give you a hand.

-PB

 

[Rocketman248]

Ultimate customer service right there.