Sudden connection/voltage problem [resolved]

[hryc111]

I was just about to post about how much I have been loving my Crack amplifier.  I can't believe how much fun I've been having!  It's been working great for 2 weeks. I love the sound. I loved building it. I'm hooked.

But suddenly I have a problem.  It coincides with my having swapped out the 5963 tube for a 12AU7 and back again.  One channel dropped out, with lots of noise but no signal. With both tubes.  Physically removing the tubes maybe loosened a connection, but I can't find it.  I reflowed a few joints to no effect.

Checking the voltages, I get this: 1 = 54 and then drops slowly to 10v over 10 seconds or so; 2 = 179V; 3 = 0V; 4 = 179 V; 5: 83; 6 = 0V; 7 = 67V; 8= 0V; 9 = 110V; 10 = 0V.

1 and 7 have unexpected values/behavior.  Both LEDs light.

Don't know if these are enough symptoms to diagnose, but any thoughts would be incredibly welcome.

[Paul Birkeland]

Can you post some build photos?  You most likely have a loose joint or something touching that shouldn't, and that's causing these issues.

[hryc111]

PB:  Attached are a few photos.  Thank you for taking a look.

AH

[hryc111]

PB:

A few more photos in case they are useful.  Thank you again.

AH

[Paul Birkeland]

Can you carefully measure the voltage at A3?

I would definitely trim back a lot of the leads that are poking out, and if you're soldering iron has adjust able temperature, it's not turned up enough.

[hryc111]

Thank you.  I ended up reflowing lots of joints, and trimming leads, as you suggest.

At first, with stock tube results remained the same. 

I tried again a recently acquired RCA 12AU7.  And worked perfectly, which I swear it did not earlier.  1 and 5 match. And 7 and 9.

When I reinserted the Beckman 5963, now I only had one LED lit and expected voltages only at 5 and 9.

Could I have damaged the Beckman tube when it removed it the first time?  I’m brand new to tubes.  Are they more fragile when hot, for instance, which it was when I removed it the first time? 

Because of the way the repair played out, I can’t be certain which changes made a difference, but repaired it is.

Your feedback is super helpful.  Will turn up soldering iron, and generally aim for neater joints.  I’ll undoubtedly be back to the Forum.  Thanks again.

[Paul Birkeland]

I wouldn't be too quick to toss that tube just yet.  Generally I would not expect something like that to happen.  If terminal 1 is around 0V and one LED isn't lit, that could possibly be an internally shorted tube, though it's incredibly rare to have a working tube suddenly fail like that.

[hryc111]

Thank you, PB.  Could it be a pin-oxidation problem?  I've tried to gently clean the pins, but maybe there's something specific about the way one of these pins makes contact in the holder.  I did notice repeatedly that pin holder A2 was especially loose in the ceramic holder, even when that original tube was fully inserted.  I was assuming it was making contact, because it had in the past and because it looks like pretty failsafe technology.  But maybe it wasn't? 

I'll keep the tube, and keep listening.  I'll hold off Speedball installation until this configuration has remained stable for a couple more weeks. 

[Paul Birkeland]

The voltage going low on pin 1 is indicative that there's something shorting rather than an open connection.  This can be debris in the socket (potentially between pin 1 and the center pin, or pin 1 and pin 2 if the terminal 1 voltage wanders depending on where the volume control is set), or something internal to that 12AU7 that's causing problems.

Also if you were to do something like use plumbing solder and/or flux on your build, you'd be treated to problems like this.

[hryc111]

One final update.  A newly arrived ECC82 tube also works without a hitch. (That stock tube will remain a mystery for the moment.). Thank you for all your feedback.  I was definitely not using plumbing solder. 

I have only clichees to reach for to describe how much I am enjoying the tube sound of the Crack with my HD600s and HD6xx: relaxed, open, rich, liquid, warm.  It's subtle but so immediately recognizable, compared to the presumably well-designed Schiit Asgard I'm comparing it to.

I love the tube sound so much, I just ordered the Moreplay to see how it plays with my old NAD and Musical Fidelity amps.  Plus I just need soldering practice!

In high school--impossibly 45 years ago--I used to build Radio Shack projects and listen to classical music and shortwave broadcasts on my dad's old Blaupunkt stereo console, which presumably had tubes.  Having a tremendous amount of fun feeling like a nerdy teenager again, with fantastic new gear.  Thanks for designs and thanks for all the support.