Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dscottguitars on February 23, 2013, 03:43:45 pm
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Hello again...
I'm finishing up this amp and have a loud buzz problem when I switch it into low power mode. It is really quiet with only slight hiss in high power, but when I switch to low power I get a nasty buzz.
The voltages on the plates are:
High-490v
Low-340v
Adjusting the bias does not help.
I've done this before but not with such a spread of 150v. The other amps I did this with were 420v down to 320v. I didn't get any more noise from them either.
Any suggestions as to why with this one?
I'm really looking for that low voltage grind like Eddie Van Halen's brown sound using a variac on the wall plug.
Thanks...
Daniel
The picture is not current. I finished hooking things up but it shows the layout. I have the bypass caps grounded because the footswitch is not finished either.
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I doubt this has anything to do w/your noise, but why do you have a switch that turns off the heater on the 5Y3?
Never mind, I see it's to be able to select between tube & SS recto.
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I think I have found where the problem is but I don't know why.
I noticed on the first drawing that the switch is not in the correct place. I put in before the main reservoir caps as shown in this drawing. My other amps are like the first drawing too. For some reason I thought it would be better with the switch in front of the caps which is the only reason I changed it.
Can someone please explain why this would make a difference? I will hook it up like my other ones tomorrow and see what that does.
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That took care of the problem. Now I would like to know why...