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In Reply to: RE: Full music TJ 300B mesh Sofia traced plate curve posted by Balle Clorin on September 01, 2014 at 14:57:36
Jim Dowdy:
What do you mean by "explored"? Research/read, or simulate, or try in practice? When making a statement, it's important to state correctly what you meant.
Research is nice but inconclusive, simulation requires precisely matched spice models to be relevant, while I sincerely doubt that you have tried in practice 100 operating points: you would need to use several output transformers in the same amp, and probably fixed bias along with a very flexible power supply!
So, in which fashion did you"explore"?Tre':
You can choose whichever operating point and load you want - as long as you do not exceed relevant parameters/limitations. You can choose 10k if you wish....
The loads and op points shown are just suggestions, documented with power output and distortion figures. But it's mere example and analytics! And, it probably addresses ONLY the output stage, while a real life amp needs at least one more stage.
With a minimum of knowledge and amp design skills, anyone should be able to choose an operating point and load to his/her own liking.
My RH300B operates at an operating point not mentioned at all in the table shown by WE (96mA current draw, 335-350V across the tube depending on the rectifier used, 2.5k load). Check it out for additional info, if you're interested.***********
http://rh-amps.blogspot.com/
Edits: 09/02/14Follow Ups:
By 'explored,' I am referring to experimentation/listening to what sounded best to me on my system. I used newly manufactured WE tubes and the vast majority of the listening was bi-amped (listening to the 300B amp above 80 Hz). Multiple OPTs were used; with cathode bias.I don't really care if you believe I have tried 100 different operating points/loads or not...perhaps it was only 75.
But that is beside the points - which are:
a) 5k is a very viable choice for use with the 300B, and
b) opinions do not necessarily converge.Your response to Tre' reinforces this reality - you state: "anyone should be able to choose an operating point and load to his/her own liking."
BTW: the operating point I settled on as sounding best is very close to your's - 'though I preferred it into a 5k load.
Edits: 09/02/14 09/03/14 09/03/14
I don't care either whether you've tried 100 or 20 operating points: but I don't like bold statements with exaggerations. Assuming you have a pair of transformers with 2 primary options and 3 secondary options, you could probably 3 or 4 different load values combining those. When you add a number of operating points (let's say 60, 70, 80, 90 mA) and a few voltage across the tube values (300, 350, 400) - we could realistically estimate that you might have tried probably 20-40 operating points, of which more than one half do not make any sense at all. Reasonable experimentation would probably not exceed those 20 reasonable operating point and load conditions: thus 100 is a very bold number...
If you like the 5k load with a current draw similar to mine, you've obviously got very different speakers than myself. I would guess they are efficient and bass heavy... and you are probably NOT using the globe "fake mesh" version: again, I guess it's either Sovtek or Electro-Harmonix. Because - at 5k the 300B sounds rather "thin" and lacking in mass.
Of course, I advocate freedom of choice and abhor the situation with 300B amps in general (commercial and DIY) which might be qualified as "replicatio ad absurdum", with the three stage cascaded driver (usually 6SN7) being rather boringly omnipresent...
http://rh-amps.blogspot.com/
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