Tube Amps / Music Electronics
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|2/7/1998 4:52 PM|
||Ampeg VT22 Cracking/Popping!!!!!!Please help!|
You know,.....I have had more problems with this amp!,....I just got it back from the shop,...the guy biased my KT-88 I bought for it. It took him 4 months to do it!,....I just got it back today. He said there was a bit of ground noise. When i got it home it started popping and cracking. I found out that a soldier joint on one of the mulican caps was shorting to the chassis. After that was fixed I turned on the amp and it warmed up. It starts to pop and hiss. When I put a guitar though it I can hear it but at certain levels it starts to make the speakers pop out and in really fast. If i back the volume is set a what seems to be a certain threshold The guitar is heard over the hum however it is distorted. If I crank the piss out of it it just sits there and hums with the guitar playing distorted loudly. When i removed the preamp tubes The amp seems stable. There are no apparent noises, or popping. I was wondering if it could be bad preamp tubes?
If you are wondering why It wasn't fixed properly in the shop. Well. the guy said he had no time to work on it. I was quite upset. Can anyone help me? Anything else I should check?. Oh yeah and when i turn the stand-by switch on the light goes on but the amp come on. When i turn it off the amp goes off and so does the light. Maybe the light is just wired wrong.
Thanks alot guys for your trouble!
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|2/7/1998 8:41 PM|
" target="_blank">http://www.eden.com/~keen/"> http://www.eden.com/~keen/
and select "The Tube Amp Debugging Page".
Of course, four months for a biasing is a poor indicator in the first place.
|2/7/1998 10:02 PM|
Hey R.G. i know exactly whats going on here regarding the standby switch mess,
the guy has screwed up the groung wiring on the multicaps.
the standby system works by lifting the ground from the caps and the 'back' of the rectifier.
i once accidentally grounded the caps directly to ground, thereby killing the standby system.
the caps/rectifier would ground and activate B+ as soon as its powered on.
|2/8/1998 7:33 AM|
I already checked out your page R.G,.....Great stuff!......you did a good job. From what I have read it seems like something in the preamp section is screwed. I pulled all the tubes and the noises went away.
I ALSO NOTED LAST NIGHT WHEN I WAS SCREWING AROUND WITH IT THAT HE HAD REPLACED A 12AU7 WITH A 12AX7. IS THIS AN EQUIV?. BECAUSE WHEN I PULL THIS TUBE OUT ALL THE NOISES GO AWAY. I ALSO FOUND OUT THAT ONE OF THE 12AX7 ARE NOT LIGHTING UP AND WHEN I PUT IT IN THE 12AU7 SOCKET IT DOESN'T DO ANYTHING AND THERE IS NO SOUND. I THINK THE TUBE IS DEAD. SO MY QUESTION REALLY IS CAN A 12AX7 BE SUBSITUTED FOR A 12AU7?. THANKS SO MUCH GUYS!
|2/8/1998 1:34 PM|
Is there a equiv for this tube?......
|2/8/1998 2:31 PM|
closest is 6Q11.
others that will work (i.e. can plug in and expect some kind of signal processing), but the gain characteristics will certainly be incorrect for the various circuits: 6D10, 6U10, 6AC10, 6C10, 6AV11, 6AK10 (this last one has a 50% higher filament current draw). depending on your exact application (which you didn't specify), i would guess that the 6C10 would be your next best bet to a 6K11/6Q11.
|2/9/1998 8:30 AM|
The 6K11/6Q11 is a tube containing three independent triode sections, one like a 12AU7 and the other two like a 12AX7. In this Ampeg circuit, the 6K11 is used as the line-level preamp, with the first two sections as gain stages and the third as a cathode follower with the active mid control in the feedback loop. The 6C10, 6D10 & 6U10 will plug in here, but the tonal response and the gain will be a little different since these three tubes have a different "mix" of internal triodes than the 6K11. A 6BK11 will also work, but that's a more difficult one to find.
On older Ampeg amps, with chassis mounted tube sockets, a pair of 9-pin sockets can be fit so that these Compactron tubes can be replaced functionally with the standard 12A_7 types. With your VT-22 (same as V-4) it's damn near impossible to do this conversion because of the circuit board.
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