1

MP566 Tube microphone preamplifier / Re: High Voltage running away

« on: August 04, 2023, 04:21:56 AM »

Sent an email your way, thanks.

2

MP566 Tube microphone preamplifier / Re: High Voltage running away

« on: July 27, 2023, 07:51:03 PM »

D14 looks good, 3V3 across it when powered up, starts to drop as the voltage across TP2 and 0V increases.

3

MP566 Tube microphone preamplifier / High Voltage running away

« on: July 25, 2023, 10:16:06 PM »

Hi.  On a new build of the 566 I'm running into an issue with the voltage between TP2 and V0 ramping up past +240V to ~+380 before the fuses cut the power.  The board pulls >1A while this is happening.  I'm using a 501 to power the board which is working fine on other kits I've built, I've gone over the troubleshooting instructions and all the components look well soldered and correctly oriented, and the tube itself looks healthy (from what I can see).  The output transformer is not on the board while testing per the instructions.  Any help you can provide would be much appreciated.

Thanks!