New build, voltage question

[MachineShedFred]

Hello!

So I just built a Reduction, and I have a couple questions.

1.  I am showing 150V on terminal 2, where the manual says it should be 70V to 90V.
2.  The red LED from the center post of socket A to post A3 does not light up, where the same LED on socket B does.

Any thoughts on what I screwed up?

EDIT:  I noticed one difference between the pic in the manual and mine:  the manual shows the capacitor between terminal 6 and 14 at 0.1uF.  The part I received is 0.01uF.  The one on the other side is the proper 0.1uF.

Would that account for the voltage change and LED not being active?

(I've attached photos of the two different capacitors)

[Paul Birkeland]

That's certainly a misprint on the label of the cap, we'll have to check our inventory to see if there are any more like that. 

One thing to try is to swap tubes to see if the voltage issue follows a tube or is related to the actual build. 

Your voltage indicates that one of the triodes is not drawing current.  If this problem does not follow a particular tube, let us know and we can direct you on debugging.

-PB

[MachineShedFred]

I swapped the tubes, and the unlit LED followed the tube.  The voltage on terminal 2 then was in the range it's supposed to be.  I don't know if the information about that LED is useful for diagnosing anything, or if the LEDs are just there to add a bit of resistance and help discharge capacitors for safety (and let you know there's voltage pumping through the thing). 

Two things I noticed after the swap:
1.  as I said, the LED that was not lighting going from the center of socket A to A3 lit up after swapping the tubes.  The LED going from the center of socket B to B3 ceased lighting up.  Bad tube?
2.  on a cold start, it takes upwards of two minutes for the tube in socket-A to start glowing, but it eventually does, then the LEDs come on, and the voltage reads 75V like it should.  This "taking forever to heat" behavior does not follow the tube - it happens on socket-A with either tube.

Sounds like there may be multiple issues?

[Paul Birkeland]

The two 5 lug terminal strips around the vents in the chassis hold the components responsible for heating the tubes.  Some parts are common to both tubes, and some are not.  Since one tube lights quickly and one does not, you will want to concentrate on reheating the solder joints on the A side of those 5 lug strips (just reheat all the joints), and be sure you have good solder joints on the shielded twisted pair feed that goes to A4/A5, which carries the 6V heater voltage to the tube itself.

[MachineShedFred]

Ok.  Progress!

I reheated all of the terminals on the 5-lug strips, and reheated A4 and A5 because I saw that the resistance on 33 was around 25 ohm, where 37 was only 4 ohm.  That got both of 33 and 37 to ~4 ohm, and the tubes both heat up at the same time now.

However, I still have twice the voltage on terminal 2, and one LED out on socket A.  Switching the tubes gets all the terminals connected to socket A into spec, but causes many of socket B to double in voltage, as well as cause the LED from center to B3 not to light up.

[Paul Birkeland]

Well, you may well have a 6922 with half the heater out.  If you e-mail replacementparts(at)bottlehead(dot)com we can mail a replacement. 

-PB

[MachineShedFred]

I've sent an email.

Thanks again for your help, hope to hear some glorious sound from this thing soon!