Favorite 300B: Sophia vs KR

Paul, yes "ma" stands for milliamperes, and in this case refers to the plate current under some given test conditions (plate voltage and grid-to-cathode bias voltage particularly; perhaps also filament voltage if that is varied from its nominal 5 volt value).

I talked to Brent about this yesterday, and I could have sworn that he said healthy tubes should measure in the 85 to 90 range.

Paul, I would feel pretty certain that what Brent was referring to was the plate current as measured in the amp, when biased by the amp.

That has no necessary relation to the 48 and 80 ma numbers the vendor quoted to Michael, because it is very likely that the test conditions (plate voltage and bias voltage especially) were different for those measurements than they are in the amp. The plate current numbers will vary dramatically depending on those test conditions. I would expect the 48 ma tube to measure much higher when placed in the amp.

The uncertainty I have, as I indicated in my previous post, is whether or not a tube whose plate current is significantly lower than average when measured under a given set of conditions (as seems likely to be the case with the 48 ma tubes), will provide optimal sonic results when biased by the Renaissance amp. I don't know the answer to that question.

BTW, do your VAC sourced Chinese tubes have any measurements marked on their bases, as mine do?

Best regards,
-- Al

Al - yes, the readings on the bases of the VAC / Chinese tubes read 45 & 5.4.

Hello Al,
The VAC REN amplifiers have auto bias, would`nt that compensate(at least somewhat) to the various ma levels?

I believe there are differ auto-bias circuits around, also how and what exactly they do, is not the same.

Charles1dad,

The new Takatsuki TA300B tubes are still breaking in. I've got 31 hours on them so far. They are truely a game changer in the Frankenstien amps. The highs are chrisp and well pronounced and the base seems much more controlled. It is uncanny how these tubes change the personality of these amps. You were right on with your observations and I want to thank you for this tip!!! I do notice improvement from session to session. I have not tried the BT's in the VAC 30/30's yet. Hopefully before weeks end I will have a chance. One set of my BT's is marked with 69ma and the other is not marked at all and worries me. The ones marked with the 69ma came from Coincident and the second unmarked pair came from an Audiogon ad and perportedly have 100 hours on them. I'm a little afraid of screwing something up. I'll keep you posted