Phase inverter tail resistor burned/smoke

[thomasdj]

Hi,

Just finished a new project..slo 100 clone with depth mod and a few extras..
When i flipped the stand by switch off for adjusting power tube bias voltage (turned to max voltage -71v) and measure general voltage suddently the 10k tail resistor was smoking!

PI pin 1 plate voltage is 330v but the cathode voltage is also 300v+!!! Was expecting 60v or so. I cannot find anything wrong, What do i have to look after

Any help would be appreciated, thanks

Thomas

[Enzo]

300v comes from somewhere. You may have a piece of resistor lead or other wire sticking out from pin 1 or 6, and touching pin 3 or 8.

Or a little bead of solder wedged somewhere, or a drip of solder between pins.

[thomasdj]

Hi enzo, thanks for you reply and i can only give you right...

There is nothing visible..without the tube i measure 40k between the cathodes and pin 1 plate and 30k between cathodes and pin 6 plate..realy frustrating

[Enzo]

So leave the resistor unconnected for now. Power up the amp with no tube in the socket. Is there still 300v on the cathode pins?

If so, turn out the room lights and look closely at the socket. See any tiny blue sparks? That would be an arc. Otherwise, turn the lights on and find where the voltage is coming from. This will not be something the schematic will help on. Unless you miswired it, we have some unwanted connection.

Make sure the tube socket is not wired one pin off or something.

[thomasdj]

I'll do that enzo, thanks. Time is 1 in the night so i'll wait untill tomorrow and let you know the result.

[Jazz P Bass]

Soldano SloClone Schematic

Is this the schematic?
Which resistor burned?
The first thing that jumps out at me (48K cathode to plate) is you may have inadvertently connected point 'C' to the cathode.

[thomasdj]

Hi enzo and jazz p.. the amp is up running now..it was solder flux! I have never had problems with flux untill now..i measured resisrance between unused (not connected/soldered to anything) traces...cleaned the board totally and now the amp is running...as you wrote enzo..300v comes from somewhere..