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In Reply to: Re: crackle!! posted by Tarbaby on February 13, 2007 at 08:43:59:
Tarbaby, hi. Don't get too bummed out about it. Your amp looks like it uses 1 12AX7 ( one section for each channel) and two 12AU7 as phase splitters. Yeah, if you haven't done try changing out the input tube. Have you tried OS or NOS tubes in these positions? Your amp uses some kind of auto biasing scheme. If this is an active bias set circuit (adjust negative voltage on output tube grids for a pre set amount of cathode current automatically) I could see this as a source of problems. Have you talked with anyone at the factory? A tech who knows your amp backwards and forwards may offer big help.
Follow Ups:
There was nothing wrong with my amps after all, it was the 12ax7's going bad causing the crackle. The reason why I overlooked the tubes is because they are under 100hrs. This is the first time a tube has crapped out on me this early, I will never buy the new Tung Sol 12ax7 again. Thank you all for your help, couldn't have figure it out without your input.
Elektron, I greatly appreciate all your help.
I will try to change out the AX7's and Au7's to see if it helps, I'm hoping this is the problem as this is a cheap fix. As I stated earlier, I have replaced all tubes approx. 6 months ago, it could be that the Tung Sol AX7's (new version) are defective or something.
I've tried contacting Audio Valve, but they are in Germany which make very difficult. These are the best amps I've had when they work, so I'll keep trying.
Tarbaby, hi again. Congrats! You solved your problem. If I were you I would try to round up some OS or NOS tubes for your amps. You won't have to mortgage your house. These OS tubes will make a good benchmark against new production ones. Try to get them from the peak years of production if you can (50's 60's). I have OS tubes used for many years that perform and test fine. There were so many AX and AU made examples of these types should be available for a long time to come.
Thanks for your advice, where do I start looking for OS tubes? ebay? The NOS tubes I've seen are up there in price.
Tarbaby, hi. It sounds like a truism, but it is always wise to know your seller. I would start with Antique Electronics in Tempe AZ (tubesandmore on the net). I would request a catalog. The folks in sales have always been more than helpful. They can walk back into the warehouse and check the bins for what is in stock. Very cool. Also, I like Michael Marx at SND Tube Sales. Mike is a one man band but he knows his tubes. I've known Mike for over 20 years. Do some comparison shopping via the net. There are some good sellers who sponsor AA. Check Fair Radio Sales in Lima, Ohio. They have a web site. Also - try to find out of there are any HAM fests in your area.
These amateur radio fests always feature a swap and shop. Sometimes it is in the parking lot a la tail gate. I know I'm forgetting a lot of dealers (no offense intended). I'm getting over a terrific cold and my mind is not at its sharpest. I would also get a copy of the GE Essential Characteristics handbook (Audio Amateur has republished it). With that book plus Duncan Amps web site you can look of at least some information on types, military/industrial versions, Euro versions, etc.
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