Tube Amps / Music Electronics
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|10/20/1999 11:51 AM|
||HELP...My Crate GT-50 Died!|
Help...while I was playing through my Crate GT-50 (4 6V6 tubes) I noticed that the volume decreased....then the sound got real farty...then got lower untill the pilot light went out and i noticed a funny smell...not like a burning smell. I pulled the tubes out one by one and noticed a burnt smell on the base of one. I know I'll have to go into the amp but does the above symptoms sound familiar enough to anyone to give me a hint of the problem.
|10/20/1999 1:15 PM|
Are you sure it´s not, just a fuse?
I know how easy it is to think it´s something more serious.
When a slow-blow fuse goes, it causes a farty sound when the voltage drops.
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|10/20/1999 5:10 PM|
Yes....the fuse did go but I believed it to be because of something else. Does a fuse go like that occassionally with no reason?? The burnt smell on the base of one of the tubes could be because of heat build up or being near the power resistor.
|10/20/1999 5:15 PM|
Sounds like you lost a tube. What kind of 6v6's was it running? When a tube arcs and shorts out, you lose the fuse and also generally (not always, though) have some damage to the power supply. Being a Crate, I wouldn't rule out a bad socket or a broken solder connection. Also check the rectifier diodes and make sure one of them isn't misbehaving.
|10/20/1999 7:25 PM|
|10/20/1999 5:27 PM|
check/replace the coupling caps to the output tubes
|10/20/1999 7:10 PM|
Could be bad sovtek 6V6s. Shit happens with those, eventually. A bad tube could have taken the OP trans with it, but hopefully not. To rule out a shorted power trans, I would pull all 4 6V6s, put in a fresh fuse (maybe a 2A fast blow), and turn on the power switch. If the fuse doesn't blow and the 12AX7s light, go through and check all the AC voltages at the transformer leads and if all are present, check all the DC supply points for proper voltage.
If all this checks out good, then I would do as Gus suggested. Replace the phase inverter to power tube grid coupling caps with good polyester or polypropylene units, plug in another set of 6V6s (even new sovteks will do), and fire it up. Check for sound. If you have decent sound, you know the output trans isn't cooked. If good, go back & check voltages on the 6V6 pins just to make sure bias voltage, etc. is in spec before buttoning up.
This is actually a pretty good amp. If you have a schematic, trace out the signal path. You'll find three places (I think around op-amp buffers) where the signal goes through some electrolytic coupling capacitors. (Yuk!) Change these out to film caps and the overall sound quality will improve.
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