Nasty noises, occilation?

[Tage]

So I have built a 100 watt amp with a parallel triode input, cathode follower, tmb tone stack and long tail phase inverter with no Negative feedback. The output stage is 4 6550's with around 500V on the plates.

I fired it up for the first time today with the bias voltage at it's max, and I got this nasty crackle and popping sound coming through my speakers, I powered down as soon as I could. Unfourtunatly the only measurment I got was my plate voltage wich settled out around 497V. I checked for any shorts to B+ in my AC signal path but I don't have any. Any suggestions for trouble shooting would be very appreciated.

[J M Fahey]

Hi tage.
Verbal descriptions are fine, but schematics much better.
Please show us what you did.
No need for fancy schematic software; a clean design on paper, scanned at a local Internet house will do very well.

[Prairie Dawg]

Could be anything at this point. It wouldn't hurt to go over it with a chopstick.