Fireworks in an Audio Research VT200

Excitement is not uncommon with tube amps. 6550s, KT-88s and especially 6C33Bs can arc across grids and take out other devices in the system. My BAT VK-60s which use 6C33B power tubes have been far less reliable than the ARC Classic 150s I enjoyed for years which used 6550 tubes. In any case it is unwise not to atleast pop the top and look for other damage before changing a blown tube and restaring your system. Sniffing the box for a cooked resister at the very least should be done. The Bats have fuses attached to each power tube and still take out resisters when they blow. I have been advised to only employ UL fuses because they are more precise. Also power amps should be checked out once in a while to ensure that the power supply voltages still meet manufacturers specs. Good luck.
Jeff

I have had that happen quite a few times with various ARC amps. Usually it is a tube arching.
Sometimes it will take out a resistor. I would definately check the tubes at least.

Hi
I have repaired several ARC VT 200 amps with this situation.
It typically starts when one of the output tubes shorts and causes an arc in the plate or cathode ciucuit. It burns away some of the conducting trace ( hence the fireball) and sometimes takes out a resistor on the cathode or screen.The related tube should be tossed out and replaced.

I WOULD NOT CONTINUE TO USE THE AMP IN THIS CONDITION.....

Right now it is an easy and inexpensive fix.
Best to keep it that way.
Good luck.

Mike

The 200 banks several tubes onto one adjustment

My VT200mk2 stopped John Denver during an immense crescendo with a tube arc & an impressive white flash of blown resistor underneath -yes that smell is quite pungent - AR do fireproof their resistors. The 6550s were about 1200 hrs in but I replaced the lot. Leonard at AR is very helpful.
Maybe I should keep a fire extinguisher at hand given the above tales! Doa nt of you have experience with tube rolling in VT200mk2?
Doctor from durham, england

From the above posts, sounded like no speakers were damaged in any incidences. I have heard drawback of ARC amp - using one pot to bias 4 or more tubes leaving one tube to work much harder than others. Other brand, like Jadis or Sonic Frontiers, give each tube individual trim pot to bias the tube and consequently reduce load differences. Not sure how true this statement is.

So the 6C33 in BAT/Tenor also arc easily like 6550? I would think if it is good enough to be in a Russian Mig, it should be build like a tank. I ask because I now own VK-150, would like to keep my house and speakers intact. What can user do to prevent arcing short of changing tubes every other week?