Fireworks in an Audio Research VT200

I would certainly like to hear about what caused this problem as I use a VT 200 in my system. My first thought was non-standard output tubes, but I assume this not to be the case. These amps are pretty picky about what they will accept in the way of tubes and tube matching. I certainly agree that I would by no means continue to play the amp until the cause can be determined. Despite the cost, I would suggest returing the amp to ARC for repair. ARC is pretty good about making repairs at no charge or at cost if they believe there may have been a component defect. Good luck.

I've had tubes blow in an ARC CA-50 & a VT100 with a loud electrical snap & a puff of smoke. In all cases the amps still worked with one tube unlit & exploded resistors next to the unlit tube. Replaced the tube & resistors & life was good again. (In one instance the resistor I "retrofited" wasn't "flameproof" & when it "blew" a very brief wisp of flame was visible.) These were all non-ARC sourced svetlana 6550c's. This has occurred once in the CA-50 & twice in the VT100 (different tube locations) I always check the adjacent resistors when suspecting a tube problem...

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