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Vox AC30 crackles

6/7/1999 6:24 AM
Vox AC30 crackles
Hi everybody!  
My mate's AC30 crackles. I pulled out the outer EL84 and it worked, no more crackling, though it breaks up earlier. After all that's what he wanted!  
Do you recommend this "half power" mode?  
Will it eventually kill the amp?  
Are the crackling noises due to bad or worn EL84s or defective cathode resistors?  
6/7/1999 8:57 AM

The bias voltage on the other tubes will be effected by removing one or more from the power section. They are self biased and depend on each other for the correct bias point and thus idle current level.  
You'll end up drawing way too much current through the other tubes if you do this and eventually ruin the remaining power tubes.  
So in a nut shell: IMO this is a bad thing to do and I don't recommend it.  
6/7/1999 5:57 PM
Bob S

If pulling the power tube stopped it, you'll need to pull all your power tubes, clean a retension all the tube sockets. This is fairly common on old AC-30's  
Bob S.
6/8/1999 5:06 AM

Having had a similar problem that plagued me for ages, I'd suggest replacing the tube sockets and all the attached resistors. When they've been so hot so many times, they don't keep their tension very long after retensioning. The resistors usually suffer too. Mine were way out of tolerance.  
I must say, old AC30's are a pain in the arse to keep on the road, and most of the problems are caused by running so hot. It drys out all the electrolytics as well.  
Just my $0.02.  
6/8/1999 7:05 AM

Would doubling the wattage rating on the resistors (i.e. 1 watt is replace with a 2 watt) make them last longer?  
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