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Ampeg SVP-CL tube choice

getdown

getdown

Oct 8, 2007
14
5
#1
I am using an Ampeg SVP-CL bass preamp, which has begun to crackle and pop intermittently while warming up. Thinking it was a tube going, I tested them all (V1-V4 / EH 12AX7, Tung Sol 12AU7, EH 12AX7, Tung Sol 12AU7) - and all tubes tested OK.
I changed them out for JJ ECC82 and 83's, but lost 80% of the gain, so I put the originals back in.
Can anyone tell me what (hopefully better) tubes I could replace the originals with without sacrificing gain or increasing noise?
 
#3
B-string said:
Sounds like one of the JJ's you received was bad. No other reason you should have lost gain. ECC83 is a 12AX7 and ECC82 is a 12AU7. If you put a ECC82 in a 12AX7'ECC83 socket you would lose gain.
Click to expand...
Nope, I kept the tubes in the correct positions, but did not try both 83's in the V1 position. I'm assuming that is where most of the gain is produced. I'll test the JJ's before I return them..
 
#5
Yep, rotate each 12ax7 in V1 till you find a culprit. I've tried many a JJ against other type tubes and never had a volume drop. Are you sure you're not using a 12au7 where you should have a 12ax7? :D

Also, it's entirely possible that there's only one bad tube in your original batch. I'd try to narrow it down and keep using the other tubes.
 
#6
UPDATE:
Indeed, one of the JJ ECC83's was hosed, although tested "good" on a simple tube tester. In V1 position, no sound out of the preamp at all.
Tapping the EH 12AU7's triggered microphonics, so I swapped them out for the JJ ECC82's, and hopefully that cures the crackling. Tone and gain are still there.
Intrested to try a Mullard in the V1 position. Anyone done that?
 
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#7
I just replaced the tubes in my CL with JJs also. The tone is fine but the gain is very low. I can turn the input gain all the way up and the clip light doesn't flash. I swapped positions of the ECC83s and that didn't change anything. I'm going to try swapping the ECC82s to see if there is a difference. I thought JJ tubes had a good reputation but maybe they aren't that great in the QC department.

Rick B.
 

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