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I have a pair of Audio Valve Challenger 140 monoblocks (similar to current model 150), these amps are a little over 10 yrs old. They started to make crackle/statics noises at the beginning of each track, especially more on recordings that are harsh.
I took the amps to the repair shop 2 weeks ago, they cleaned up the inside and some of the crackle is gone. Some crackle still remains, I would love to get rid of all these unwelcomed noises. Please let me know what I can do? I have retubed both amps. I will be taking it back to the repair shop in a couple of days, what should they check?
Anyone have this problem before?
Thanks in advanced.
Are you sure that the crackle you are hearing is due to the amp(s)? It could be that you fried your speaker tweeters because it seems strange to me that BOTH of your monoblocks would exhibit the same problem. Maybe you got carried away with volume and fried your tweets. Just a thought. Good luck.
At first I thought it was my tweeters, but after hooking up three different speakers to the amps, I'm certain it's the amp.
Both amps exhibit the same problem, but not simultaneously, one more than the other.
Tarbaby, hi. If your amps employee a large mother board on to which are soldered tube sockets, the solder points being the only means by which the sockets are attached to the board, I would start there. Is the crackle sound audible in both amps simultaneously? That would be a clue as to origin - if not the amps. I would carefully resolder/reflow all tube sockets. If your amps used lead containing solder (probably a 100% chance) I would remove the lead bearing solder and rework with a tin/silver activated rosin core type - say 96.5% tin 3.5% silver. Lead bearing solders can crystalize and do other funky things after 10 years of thermal cycling. Next - make sure all ground paths are not intermittent. Take the time to clean and retension all tube sockets. If the sockets are merely solder attached hold the socket with one hand when inserting or removing tubes. Pulling on a board mounted tube socket subjects the solder joints to damaging stress. How is audio sent to the mother board? If by simple wires soldered to the board reflow those joints. All the best in finding the problem which may come down to the grid 1 pin of the input tube and some crud in the socket. I would also obtain some DeOxit or equivalent and with pipe cleaners and swabs clean every socket carefully. Clean the input jacks too.
elektron, thank you for your response.
The crackle sound are audible in both amps but not simultaneously, one amp more than the other. I do remember seeing a board, but not sure how the tube sockets are connected to the board, I will check when I get home. I am efficient with a solder iron and do have some silver solder on hand, so perhaps I might be able to fix the problem following your advice. I have done the deOxit thing which brought improvements but didn't solve the whole problem. Didn't understand the "grid 1 pin of the input tube" part.
Tarbaby, hi. Grids #1 = control grids. I was making reference to the tube pins (and socket pins) that carry the audio into each triode section - the most obvious place the signal could get garbaged up. If the DeOxit treatments plus cleaning yielded improvement this result is significant. ie - more an interface problem (pin to socket, wire to board) than an errant tube, etc. Even a poorly conducting center pin of an RCA plug (dirt, oxide, crud) could cause the symtoms you described.
I checked the amps yesterday and the tube sockets are soldered directly to the board. I performed thorough cleaning of the sockets, and solder joints, joints seems to look ok but there are some brown crud in close proximity to the joints which I think is flux.
After the cleaning I let the amps warm up for an hour before play, unfortunately, the crackling is still there.
At this point, I'm hoping it's the tubes (don't think so, just hoping)the repair shop said that the JJ's I use are crap, and they will try it with some of their Ruby tube. Just kinda bummed out now :-(
Any other suggestions?
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.
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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