Hi guys-
Just put together a Ceriatone Overtone and have an issue, seems to be a little more technical expertise on this board so I thought I would post here as well as the Ceriatone board.
With no power tubes inserted my B+ plate supply is 420v or so. In this condition, the preamp circuitry works as expected, the signal @ the preamp out is clean and all is good with the world.
Inserting the power tubes (biased as off as possible) drops the plate B+ to 330v or so and there is what looks like modulated power supply hum in the OT output signal. Signal level and controls do not alter the hum content in any way.
I have tried a couple different pairs of 6L6s, they both behave the same.
Any thoughts?
Thanks in advance!
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Cinstan wrote:Hi guys-
Just put together a Ceriatone Overtone and have an issue, seems to be a little more technical expertise on this board so I thought I would post here as well as the Ceriatone board.
With no power tubes inserted my B+ plate supply is 420v or so. In this condition, the preamp circuitry works as expected, the signal @ the preamp out is clean and all is good with the world.
Inserting the power tubes (biased as off as possible) drops the plate B+ to 330v or so and there is what looks like modulated power supply hum in the OT output signal. Signal level and controls do not alter the hum content in any way.
I have tried a couple different pairs of 6L6s, they both behave the same.
Any thoughts?
Thanks in advance!
I dont care for using the chassis as a ground but....
Sounds like the main filter cap bank ground is broken or not hooked up
Or the transformer is not rated correctly
It seems that too much current is flowing somewhere to pull the voltage down like that. Just remember that current through a resistance causes a voltage drop across that resistance. So take some measurements around the power section with the tubes pulled and then again when they are in...when you find some weird voltage drop across a resistance when the power tubes are in...you've found where the current is flowing...then it's just to figure out why.
Thanks to drz400 and Fischerman.
It turned out that both of the main filter caps were open! This design has two 200Uf caps in series for the first stage of filtering (OT primary).
I had jumped each one independently to no avail, I jumped them both on a whim...all is right with the world again, go figure.
Thanks again for the good advice guys!
Stan
