Crack hum and jack voltage

[jaytee]

I just moved my good working speedball crack from one room to another. Upon turning on, the headphone output had a faint hum that became loud within a couple of seconds. I turned it off and checked all voltages. They were Okay, but when I checked voltage at the tip of the HP jack, in a few seconds it went to 17vdc then dropped to zero. Repeated and got same results. Any ideas other than possible bad ground? If it is just grounding, where should I reflow?
Thanks

 

[jaytee]

OK, i just reflowed everything I could get to that may have been suspect. Still the same problem, but noticed that using some cheap headphones allowed me to listen to what the hum was doing which sounded more like an RF issue. When I would move around the hum pitch would change. Also, when turning up the volume pot, it would get louder, then it all of a sudden went away. The hum was loudest when at it's lowest setting and would sometimes go away as you turned it up, then would go away again at max volume. No consistency. Weird stuff. So I try different tubes and found that the stock 6080 tube worked okay but almost every tube I tried would hum at least upon turn-on including a tung-sol 5998. Then I found one tube that was dead quiet even at turn-on. An RCA 6AS7G. No hum at all. Any ideas? The other tubes used to work great. I still believe something is wrong, just don't know what...

 

[Deluk]

Maybe take it back to its original position and see if it goes quiet again?

 

[Doc B]

Sounds like it might be a volume pot issue.  Try reflowing the connections to the volume pot.

 

[jaytee]

I tried both above suggestions. Same thing. Why would it work fine with a 6A7SG but not a 6080? If the pot is bad, wouldn't it act up with any tube?

 

[fullheadofnothing]

When was this kit purchased?

 

[jaytee]

I've owned the basic crack for quite a while. Don't know exactly, but the speedball kit was within the last few years...Curious as to why you ask though!

 

[fullheadofnothing]

Post the name your order was made under and I can look it up.

 

[jaytee]

The name that the SB kit was ordered is John Trujillo in Riverside, Ca which is who I am. The basic kit was ordered in a group and do not remember the person who did the ordering. All I remember is his name was John as well. Just don't remember his last name.

 

[fullheadofnothing]

There was a bad batch of MJE350s in early 2014. You ordered your Speedball on 3/10/14. Your order shipped on 3/24/14. Those dates are within the known window of bad MJE350s, and therefore should be replaced. Either order them yourself or contact replacementparts at bottlehead dot com

 

[jaytee]

Wow, really? Okay, I'll contact you guys for those parts. What are the symptoms of those transistors being bad?
Thank you Joshua

 

[Paul Birkeland]

Hum/noise.