need troubleshooting help

[aragorn723]

Thanks for all the responses.  I guess the first thing to do is take out the black gates.  After that:
1)  check voltages at A5/B5 without the 150uf cap
2)  check voltages with the 150uf caps in with alligator jumper clips

Hopefully the numbers will be good!

Wish I knew why the numbers were out of whack though, its good to have a root cause on these things

Dave

[aragorn723]

Hi,

The numbers with and without the 150uf caps are about the same:

IA/IB     30.1v / 30.1v
A6/B6    29.97v / 19.7v
A5/B5    1.82v / 1.40v

Looks like something funny on the A6??  Any thoughts?

Dave

[Paul Birkeland]

You now have bias voltage at least. What are your battery voltages?

[aragorn723]

Hi Paul,

The 9v batteries are at 7.5v each, and the D batteries are at 1.5v each.  Thanks,

Dave

[Paul Birkeland]

Your 9V batteries are dead.

[aragorn723]

What about A6?  That voltage is 29.97 and should be 9-21.  A5/B5 are a little low.  Is there another issue here?  Can the Quickie be safely run this way, or should I still be troubleshooting?

Dave

[Paul Birkeland]

I would put in a fresh set of 9V batteries, then remeasure your voltages.

[aragorn723]

With new batteries:

IA/IB     36.76v/36.5v
A6/B6    36.3v/23.54v
A5/B5    1.869v/1.795v


Dave

[Paul Joppa]

Back on the first page, I see you did not have this problem; both plates were at a suitable voltage. From that I conclude the PJCCS is, or at least was, working correctly. If the PJCCS were shorted on the A6 side during the preceeding page+ of discussion, you would get these measurements. Not saying that's the problem, just trying to get some perspective.

[aragorn723]

Hi Paul,

Any suggestions where a short could be?  Maybe by accident during probing (an accidental bridge from pin to pin on the socket tube maybe?)  One thing worth noting, the only joints I touched were the connections for the bias caps.  I tried to pull the original caps out without using a solder removal tool, and heated it up quite a few times to do this (probably not the right thing to do).  Could it be that the 1k got thermally overstressed and that's why the cathode voltage is off?  (Would this impact A6 potentially too?)

Thanks,

Dave

[Paul Joppa]

Sorry, the last note was quick without looking closely.

A5 and B5 are the correct value, indicating that the current source is working properly. If you swap the tubes, do you get the same result? It may be a weak tube, or one not yet run in.

[aragorn723]

Hi Paul,

Here are the voltages with swapped tubes:

35.6v / 35.62v
35.48v / 21.7v
1.86v / 1.73v

Thanks,

Dave

[Paul Joppa]

This makes no sense to me! Must be missong something.

Try swapping the PJCCS outputs that go to A6 and B6 - if it's not the tubes, it must be the plate load (?)

[aragorn723]

Just want to make sure i got this right-desolder a6, and jumper that wire to b6, then desolder b6, and jumper that wire to a6?  Thanks,

Dave

[Paul Joppa]

Sorry, I didn't look at the manual so that wasn't clear. I want to move the PJCCS wires to test whether the current source is at fault.

In the manual, OA goes to A2 and OB goes to B6 (pins 2 and 6 both go to the tube plate). Just swap those, OA to B6 and OB to A2. Check voltages at A2/6, B2/6, A5, and B5. Better check A3 and B3, too - these are the grids and should measure near zero volts but let's be sure.