Tube Amps / Music Electronics
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|previous: Enzo Maybe yes, maybe no. The plate cap... -- 8/20/2003 5:57 AM||View Thread|
|8/20/2003 3:42 PM|
|hasserl||Re: Tracing down source of static|
Thanks for the reply Enzo.
The amp is a Carvin Vintage 33, I can email a schematic to you. The tubes were the first thing to be subbed, even by the owner before he brought it over to me. Then I have subbed and swapped them till I am sure it is not a tube.
The amp does have two speperate channels, each with it's own eq. The input signal is split to both sides of the first 12AX7, from there it travels to the seperate channels. After the tonestack and volume/gain controls of each channel the signal flows through a channel select relay, then the signal from only one channel travels on to the effects loop, reverb and PI. The noise can be controlled by the first volume control of each channel.
I do not have a scope. But I have ground the grids of the tubes (no CF's) and this will eliminate the noise, even the the grids of the first. Everything seems to point to the input, but I am struggling to see where it could come from.
Since my last post I did pull the offending caps, rendering the clean channel and reverb inoperative until I get replacements (hopefully today). The DC volts at the input have dropped to ~.7, whether as a result of pulling the caps or incidental. But as I worked thru the amp checking voltage readings the noise lessened until it was not bad at all. A recheck of the volts at the input were down to ~.03 and lower. Then the noise level started fluctuating, when it became louder the DC volts at the input always increased and when it was tolerable the volts were decreased.
I know that sometimes when troubleshooting things you can get into a wild goose chase that consumes time and leads nowhere. I think I may be doing that now, but there does seem to be a correlation between the noise and the DC volt level at the input. Something is causing the noise, and it seems to be located right at the beginning of the circuit, and there is very little there to go wrong.
|MBSetzer Maybe the small bit of DC at the in... -- 8/20/2003 5:56 PM|