Crack Voltage Issues - T2,3,4 - Mild buzz

[architect5150]

My voltage checks read for the following:

2 - 147 - supposed to be 50-100
3 - 81 - supposed to be 0???
4 - 147 - supposed to be 50-100

Could this be what is causing a slight but noticeable buzz that is the same regardless of the volume? Could this be a bad 12AU7 tube?

This is the only thing I found out of spec. All resistances checked out. Other voltages were on the high end but within spec. My house gets around 126VAC so the math checks out on why they would all be a little high .

EDIT: The sound is great otherwise, and the LEDs light up perfectly fine.

 

[Paul Birkeland]

You should never, ever listen to an amp that doesn't pass its voltage checks.  The voltage checks are there to tell you whether the amp is safe.  Your amp is not safe.

I can recall doing a repair of a Crack a few years ago.  The owner left a note that his amp didn't pass its voltage checks, but he plugged his headphones in anyway.  He fried the right driver on every pair of headphones he owned! (All for a backwards capacitor)

I'm very curious about your statement that terminals 2 and 4 should be 50-100V.  Could you take a screen shot of the manual where you see that and post it here?

Terminal 3 touches the chassis.  If you have 80V here, you have big problems.  The biggest cause of this issue is where the black wires meet at the headphone jack.  If one is loose in the bunch and not well soldered, you may end up with this problem.  This is also a bit of a safety issue.  You must not use your amp until this is resolved.

 

[architect5150]

UPDATE: All voltage checks pass now. I tightened the living s**t out of the transformer screws and added just a drop of solder between the grounding tab and star washer and everything checks out now. I was incorrect in my earlier post, I had said 2 and 4 and meant 1 and 5. Regardless, all voltage checks pass now.

I have 85, 176, 0, 176, 85, 0, 115, 0, 115, 0

There is still mild (not loud, not soft) buzz in both channels that stays the same regardless of volume. When I pull out the 12AU7 tube and turn the amp on the buzz goes away pretty much completely.

Does this mean it's the 12AU7 tube? When I received the tube, one of the pins right next to the gap was bent a little (can't remember if it was 1 or 9) so I moved it back into place.

I am going to pick up some 96-99% pass 12AU7 tubes from a guy here in a couple hours to check, just wanted to see what people think before spending the money. I know they are cheap but I'm a tightwad haha, hence the reason I built the Crack!

 

[Paul Birkeland]

There is still mild (not loud, not soft) buzz in both channels that stays the same regardless of volume. When I pull out the 12AU7 tube and turn the amp on the buzz goes away pretty much completely.

That's a great way to destroy your 6080, please don't do that.

Does this mean it's the 12AU7 tube?

No, pulling out the 12AU7 causes the amp not to pass any signal, it also causes your 6080 to draw a ton of current, and eventually you would hear the sound of your 3K resistors crackling and smoldering until they blew apart.  You likely have a solder joint on a filter capacitor that isn't solid, or the junction of the black wires on your headphone jack is not properly soldered.

I am going to pick up some 96-99% pass 12AU7 tubes from a guy here in a couple hours to check, just wanted to see what people think before spending the money. I know they are cheap but I'm a tightwad haha, hence the reason I built the Crack!

It will cost you no money to go over your solder joints and find the one that's causing your problems.

If you used 12U as your ground terminal and you got 80V at terminal 3, tightening up the transformer hardware didn't directly solve your problem, but rather it likely moved a loose wire to allow the amplifier to operate temporarily.

 

[architect5150]

Thanks, the issue has been resolved!