Cap upgrades (bear with me)

[BNAL]

In my Crack I glued PVC plugs to the chassis and used wire ties to hold the caps in place. This way the caps cleared the electronics and I could still remove the chassis from the base.

From your description of your problem with the left channel going out it sounds like a bad solder joint. I would suggest looking at all the solder joints in the left channel and reheat them.

[adamct]

I agree about the bad solder joint, but the odd thing is that my Crack was working perfectly before this, and I only had 4 solder joints to install the caps. I've redone them each about 3 times now, and they never looked like there was anything even resembling a problem there in the first place. If I didn't know how to solder, it would be plausible, but it seems strange that I would suddenly become incapable of making a clean joint, even after re-trying it 3 times, when before I built the whole Crack without a single problem. I also find it odd that each time, the amp works fine for 15-20 mins, and then the left channel fades out, even though I haven't touched or imparted any vibration to the Crack. Anyway, I'll try again...it must be a bad joint somewhere... Caps can't be defective, can they?

[earwaxxer]

I admit 'fading out' sounds strange. What happens if you crank it up for awhile. Wondering if that would 'heal' it, ex. if it was a cap. I guess a cap could be bad, others would have to chime in on that.

[Paul Birkeland]

Adam,

Measure the voltages after the channel cuts out, then report back.

-PB

[adamct]

I've tried that, although only for about 10 minutes and not that loud. I'll try that if it still isn't working (I re-glued the "feet" and am waiting for them to set).

[adamct]

Will do. Thanks.

[adamct]

The epoxy on the feet had set, so I just fired up the Crack. Back to both channels working. We will see if it holds. In any case, it sounds great.

[adamct]

Well, that didn't take long. Back to one channel.

Time for dinner, so I will measure voltages later. So frustrating...

[adamct]

If it is one of the tubes, any idea which tube is the more likely culprit?

[Paul Joppa]

If it fades out slowly (several seconds) I would suspect the solder joint at pin 4 or 5 of the driver (12AU7). Each triode of the driver has its own heater, one goes from 4 to 9, the other from 5 to 9. You should be able to test this by observing the tube carefully - can you see both heaters glow when both channels work, and can you see them both when one cuts out?

[adamct]

OK, checking all the voltages will mean I'll have to de-solder the caps, then resolder them using new fly leads after I've removed the chassis from the case. I have an absolute ton of work to do tonight, and simply don't have the time for all of this. I just reheated the cap solder joints, including the joints on the leads I installed, all to no avail. Only sound from the right earcup. I'm frustrated beyond words, but so be it. I'll have to tackle this later in the week when I have less work. Frustrating, because I was hoping to listen to the Crack while I worked. Frustrating, because I have no idea how this can happen. The thing was working fine before this, I only changed four solder points, and those joints are all good. And I don't understand how the sound can repeatedly fade out in one ear cup, then come back again for no apparent reason, then go away again. All without any noise or static or pops or whatever. It just doesn't work. Maybe it is the driver heater as Paul suggested, but I can't figure out how/why that would suddenly go bad. Anyway, I'll investigate later. Grrrrrrr....

[adamct]

Grainger,

Any advice on what wire specifications I should look for? Maximum voltage rating, AWG, insulation material (Eric suggested Teflon, but any other suggestions)?

Even better, do you have specific wire you recommend?

Best regards,
Adam

[corndog71]

I would suggest putting the stock caps back in if you still have them and then rechecking all of your voltages.  At the very least it'll give you room to work and you can rule out the new caps if the problem continues.

Other things to consider:  Hopefully you're removing the tubes from the sockets before resoldering connections.  I recommend using a desoldering bulb for sucking out the old solder before adding fresh solder.  I know the leads on the esa caps are stiff.  Be sure they're not bumping up against the nearby pins.  Check all connections in the power supply.

For wire I recommend homegrownaudio 22awg copper w/ teflon insulation.  Very easy to work with and sounds great.

[adamct]

Thanks for the tips, Rob.

[Grainger49]

Grainger,

Any advice on what wire specifications I should look for? Maximum voltage rating, AWG, insulation material (Eric suggested Teflon, but any other suggestions)?

Even better, do you have specific wire you recommend?

Best regards,
Adam

The voltage rating should be 600V on SO or SJO.  However if you are not in the states you are not looking at AWG (American Wire Gauge) and NEC (National Electric Code) rated insulation.

Well, crap!  No, the caps see a high voltage.  But if you can get a foot of 16/3 SO cord.  That is the black lamp cord, three conductor, that is used for extension cords.  Also, if they have SJO cord that is just a better outer insulator. 

You should just strip away the outer covering and use the white, black and green inner conductors.