114.78.27.111
In Reply to: RE: your favorite driver tube for 300B posted by cboy on November 21, 2009 at 20:29:30
CheersiesIt has / did. I mentioned it in my (typo-ridden) post. I just checked the EML datasheet (it has been a while) the 20A/B is a 5v, high mu (for a DHT at ~ 20, which is higher than the 18 I recall) tube. It requires (quality) DC for the filament/cathode, high-ish plate voltage and moderate current, is likely relatively microphonic, requires consideration regarding chassis layout and vibration mgt., has moderate impedance (~3k5 - 4k5), is available form only one supplier, and yet may still require an additional stage of gain to drive the 300B depending on the output of your source and the voltage you require to drive the 300B to the levels you desire. The 20A looks like a nice gain tube; the 20B - by my thinking - does not quite cut it as a driver in an i/s transformer-coupled circuit.
For me, potentially needing a gain more than 20 and thinking that a driver impedance of ~ 1k5 may be 'better', a three-stage amplification chain with a 45 in driving position may be a more suitable option. That said, for you, in your system, the 20A/B may be the money. Just consider whether the anticipated gain structure and output power will likely be satisfactory for you - a couple of dB may not seem much, but when you are on the edge...
I do agree with the other posters who have stated that too much gain may not be a good idea. Could you let us know what kind of drive voltage will be available at the input of your power amp? What type of music do you listen to, at what levels, and in what sized room?
Cheers
RP.S. I will go back and tidy up my previous post.
"As long as we have any intention to be right... we should be wary. So long as words have the slightest ego attachment, they are dishonest."
Charlotte Joko Beck
Edits: 11/21/09 11/21/09Follow Ups:
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