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Help..................... I am a little worried.

I am hearing a strange sound in my system that sounds.......well it's hard to discribe but, maybe a coughing, crackling kind of thing. It's not real loud, and I only hear it when I am not playing music. I have had some problems with my power amp (VT-200) blowing some tubes in the past, so I am thinking it might be something with it. The thing is ARC just went over it (about 2 months ago)and said everything is fine and installed all new tubes. I wonder though "Is everything fine"?

Does anyone have any ideas for help on this one. Could it be something else and how do I figure out what's causing this. Needless to say I am a little worried........ If it is the amp shipping this thing from TX to MN. isn't cheap.
cmo
zaikesman
3,017 posts
 
Is the noise in one channel or both? The most common causes of intermittent noise, a bad tube or a bad connection, are often channel-specific. If the noise is in both channels, then look at any small-signal tubes shared by both channels. If the circuit is all dual-mono, then a problem showing up in both channels wouldn't be caused by one bad tube.
rhocken
18 posts
 
Even new tubes can be bad. Had the same thing happen with my CJ power amp. I called CJ and spoke to Mr. Johnson who advised me that it was likely one of the input tubes. He mailed a new input tube to me at no cost. I put it in and voila, all was well! My guess is that you have a similar problem. Cracking and hissing sound. See if you can isolate it to one channel and then swap the input tubes. If it travels to the other channel, then you will have isolated the problem.
cmo OP
471 posts
 
Thanks for the advise. I will call ARC tomarrow, in the meantime it does seem to be comming from the left channel only. Trouble is there are 8 power tubes and (I think) six driver tubes in one channel of the power amp......... looks like I have my work cutout for me.
kkursula
95 posts
 
To find out which tube, turn the amp off, remove all power tubes (4) of that channel. Replace them one by one, and at the point when you get to the bad tube(s) you'll know. Do not forget to turn the amp off in between doing it.
unclejeff
1,313 posts
 
All of the above responses are correct. Before you start changing out tubes, I suggest you draw yourself a diagram of tube sockets and number them. Next, label your tubes alphabetically. So, 'A' is in hole '1', etc. Also this will help if you think you might get the wrong tube in the wrong hole.

I know this sounds a bit redundant, but if you have never done this, you might feel more comfortable and you might not be encouraging any regrets.

First, I would swap everything to see if the sound moves from one channel to the other. Then I would start swapping tubes back, one at a time, until....Bingo!
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