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Sure, run the 300B at a 45-like current to voltage ratio.

Most of the negative comments about 300B sonics are from folks who have heard them driven by crappy drivers and running rather classic-like operating points and low loads... looking for higher power.

Thorsten, Gordon Rankin and Dennis Fraker amongst others have recommended running the 300B at operating points closer to 45-like current:voltage ratios. Gordon suggested it as a way of getting close to the 45 sonics, but with more power and greater dynamic capability (and to my mind, lower distortion for a given output level). Just realised that Thorsten mentioned similar in a thread below.

These a my stream-of-consciousness thoughts about what I would do:

Run the 300B at roughly 50mA bias, 350 volts on the plate for a 1mA:7V ratio (still not quite as high as the 45, IIRC) and low dissipation. Give it a 5K load. You should get a nice 6W or more out of it. I'd also consider using a 6K or 7K load - power would drop back to 5W or less. Try AC filaments first... but you would need a quality hum pot with fine adjustment (not the clunky 100 Ohm POS most use). If this was too noisy, you could try DC filaments with CMC... or even consider a switch-mode supply, which would provide AC heating of sorts at very high frequency (and is easy to implement - though I still have concerns about "noise").

Edits: grammar and a few additions.

Gotta run.


"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki


Edits: 04/03/14
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