Just wondering about biasing this 65 bass head that I just re-capped and re-tubed with new 6CA7's. There's only one trim pot, is that the adjustment or do I need to read across the emitters? Also, knowing the high PV on these, I'm with some skepticism planning on using my bias meter if in fact that is a bias trimmer(reads from my DMM). Anyone else dare use theirs?
Thanks
Yep, dat's the trimmer
The plain sixty-five bass head only has one trimmer - bias. You're supposed to aim for 25mV across each of the 3.9 ohm emitter resistors. In reality you will probably not get exactly 25mV on both in which case you adjust the lowest to 25mV. The higher should not exceed 55mV according to the service documentation. I would probably not use a bias probe on these amps as the amplifier circuit is not designed in the traditional way. On the older style MM amp with the tube phase splitter, a bias probe may be used (taking the proper safety precautions of course).
When adjusting bias, always remember: Power setting on 'hi' and let the amp warm up for at lest 10 minutes before fine-tuning.
Sincerely,
Lars Verholt
Thanks Lars,
Thanks Lars,
There's only the two 100/450's under the dog house which threw me off a little at first but that's all it needs, no tube driver. I did however rewire the new ones to the two vacant outer eyelets and ran a jumper between rather than cramming everything to the center.
Thanks again, GW