Hi there,

I just finished my first build and I'm having some problems. It's Ceriatone plexi super lead 100watt. The amp is running way to hot even when I bias it for 60% plate dissipation. The V5 & V6 power tubes are flashing red when ever I push the amp and there is a nasty buzz coming from the PT. I've measured the plate voltage at pin 3 of the power tubes and I'm getting 518VDC. According to Nik it should only be about 460-470VDC. I'm also getting 3.45VAC for the heaters, this should be 3.15VAC.

The amp is pretty much stock except for a couple of minor tweaks : Reduced Screen filter Caps from 50+50 down to 32+32, I bypassed the voltage selector (I'm in Australia so I routed the 240V tap straight to the mains, Point "C" on the layout diagram, and tied off the 100 and 120 volt taps with heat shrink). Ive used the voltage selector switch to make the Negative feedback loop switchable from 4 to 8 to 16ohms rather than just fixing it at the 8ohm speaker tap.

I can't see anything obvious and Ive checked all of my connections a number of times. Could I have the wrong voltage tap from the PT, I used the red wire labeled 230V on the layout (Australian wall voltage is 240VAC @ 50Hz 10Amps).

I geuss I jumped in the deep end with this build but I've been very methodical about it and have spent nearly a year researching before I started the build.

Nik has been very patient and helpful, but I thought I might get a few more ideas from people.

If anyone thinks they have an answer, please drop me a line.

Cheers

Scott

Is your PT tight to the chassis.?
518 on the plates is really getting up there. It is possible your tubes do not like that much voltage. What tubes are you using and what numbers are you seeing for the current in your power tubes.?
Best