I have a friend who is going to bring me an amp to look at that is frying tubes. I suspect an issue in the bias circuit obviously, but would like a schematic to compare to. I am not wanting to rip off anyone's design, merely service the amp properly. It is a VHT Pitbull 45watt(?) 40 watt(?) I am hoping for some voltage references, etc.
If it is not a problem to PM me a copy of the schematic, I would appreciate it. He had this amp re - tubed and got three jobs out of it before the tubes fried again. TIA
Tubes red-plating
Moderators: pompeiisneaks, Colossal
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marcoloco961
- Posts: 356
- Joined: Wed Feb 25, 2009 3:07 pm
- Location: Colona, Il. U.S.
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marcoloco961
- Posts: 356
- Joined: Wed Feb 25, 2009 3:07 pm
- Location: Colona, Il. U.S.
Re: Tubes red-plating
This must be a hard to get schematic. I guess I'm going in blind..........LOL. Hope I don't find everything covered in HAD goo. That would really suck. How the hell do you work on an amp that has had it's board covered in goo? 
Re: Tubes red-plating
Marco,
That is one amp I don't have a schematic for to help you out sorry.
That is one amp I don't have a schematic for to help you out sorry.
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marcoloco961
- Posts: 356
- Joined: Wed Feb 25, 2009 3:07 pm
- Location: Colona, Il. U.S.
Re: Tubes red-plating
It must be pretty well protected, I can't find a copy anywhere. No worries, I'm sure I will get it figured out once I get it here. Gut shots anyone............LOLM Fowler wrote:Marco,
That is one amp I don't have a schematic for to help you out sorry.
Re: Tubes red-plating
It could also be leaky coupling caps from the PI to the output tubes. This can cause the bias to be off and even cause grid current in really bad instances.
That said, I would expect only one side to go RP if it were a coupling cap as the probability of two going leaky at the same time is pretty low.
That said, I would expect only one side to go RP if it were a coupling cap as the probability of two going leaky at the same time is pretty low.
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marcoloco961
- Posts: 356
- Joined: Wed Feb 25, 2009 3:07 pm
- Location: Colona, Il. U.S.
Re: Tubes red-plating
Thank you sir. I will keep this in mind as another thing to look for with an amp that is red-plating. You were correct, both sides were red-plating, turned out to just be a bad solder joint on the cathode ground to the resistors. I appreciate your advice. Pretty awesome amp after it was up and running.TheGimp wrote:It could also be leaky coupling caps from the PI to the output tubes. This can cause the bias to be off and even cause grid current in really bad instances.
That said, I would expect only one side to go RP if it were a coupling cap as the probability of two going leaky at the same time is pretty low.