Tube biasing for ARC and fender equipmen



In my fender hot-rod delux amp, I recently swapped the stock sovtek 5881 6l6 tubes for some svetlana 6l6gc's. I checked the bias, and it was at 80mv instead of the 60mv it should have been at. I next put the old tubes in, and noticed they were at the prescribed 60mv. I put back the new tubes, and lowered the bias so they too were at 60mv. I guess i learned to turn the bias DOWN before putting new tubes in. Should these tubes be run at 60mv as the old tubes were ?


1) Is it safe to put a set of Svetlana kt88's in my vt100m2 amp? It currently uses Svetlana 6550C's with bias point of 130mv. According to everything I have read, it is a safe swap.
2) Also, should I set the bias point the same with these tubes, and is there anything else I should do to the amp ?
I've been running kt88's in your ex-VT100, and it hasn't blown up yet. Leonard at ARC said that it was a safe swap, and that the bias voltage remains the same.
However, Kevin Deal did have to exchange my first set of 88's for a "hotter" set. I couldn't turn the bias voltage high enough with the first set.
Thanks Marc,
What did you think of it compared to the stock tubes ? John.
John, The 6L6/ 5881 tube In one of my ARC amps I set for .65ma. I have had no problems at this heater setting. Of course even better sound is attainable at higher ma. settings, but MELTDOWN will occur inside the tube.
The KT-88 tube is generally more lush sounding than the 6550. Some swear the 6550C is the most accurate though.
I have tried both KT-88 (from Kevin Deal through the grapevine of Audiophile friends) and 6550C -- I think KT-88s are nice, but I prefer the 6550Cs. I have went with warmer / lusher tubes in my pre-amp, and I think that the combo was too much. It all depends on your system & ears. The KT-88s will work, I have heard that they may be less stable than 6550C, also be sure to turn the bias WAY down before inserting them -- have heard of an occasional screen grid resistor blowing (also true with 6550s). Good luck!!