What 300B tubes are you using in your VAC amps?


Hello.....I know Kevin Hayes voices his amps for the Golden dragon tubes. I am currently using Sophia carbon plate tubes in my 70/70 and like them very much. KH says they should perform fine. But I will have a pair of VAC 140's soon and I was wondering what others are using and why.....also I have Brimar CV1988's for drivers.
wavetrader

Showing 1 response by raquel

"I ask because KH recommended the CP's over the mesh plate".

This suggests that Kevin Hayes might recommend meshplates as an option for the Renaissance amps in some circumstances -- he in fact warns people to never use them, as they cannot handle the plate voltage of the Renaissance circuit. Kevin speaks of one owner who has had success running meshplates, but it was against Kevin's recommendation and is to be viewed as an anomaly.

What the above poster states about the Renaissance amps running 300B's hard is true -- 95% of the WeCo spec maximum voltage. I've owned VAC Renaissance amps for eight years and they require carefully vetted output tubes. In fact, Sophia used to market a special set of the Sophia tubes for VAC Renaissance amps, which were the basic Sophia tube, but carefully tested at plate voltages that resemble the voltage that 300B's see in the Renaissance circuit. Generally, as for transconductance, 300B's for the Renaissance amps should test in the 3,000-5,000 range. In addition, the plate-to-cathode voltage for 300B's in the Renaissance amps is approximately 430 volts dc, with idle current approximately 85 to 90 milliamperes in a self-bias (cathode bias) circuit. Again, this is approximately 5% below the maximum rating for the WeCo spec 300B. The milliamp and transconductance testing for purposes of matching must be done at these voltage levels, or you will find out the hard way, when your amp starts imitating a popcorn popper, that your 300B's didn't make the cut.