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In Reply to: RE: Clean and simple! posted by maxhifi on November 22, 2014 at 20:57:45
Kiss rules !! Nice thread.I wonder if it would be a good idea to use a grid choke to ground, on the 2A3's grid, so as to avoid a high value resistor there ?
My original audio mentor, Bob Fulton, HATED the usually-used 100K Ohms and above Ohmic value at that spot, preferred to have 20 K as grid-to-ground resistance on a 2A3's grid, to "put the grid in control" or to " center " the grid and the tube's operation.
Of course, this took a tremendously powerful driver stage to pull a 20 K grid to ground. I built it!! The sonic results of lowering this grid-to-ground resistance was a more engaging music presentation. I recall "sensing the musicians in the room, playing for ME" more-so, as I went lower in value there.
It was better to hear !!
Now a well-wound quality grid choke will allow you to have, what the EEs call a high AC impedance I believe, and a superbly-low DCR to ground, that the 2A3 grid will "love" to respond to, musically.
FWIW : Fulton would use terms such as " Puts the music grid in control of the tube, or CENTERS it on the music signal ".
No flames requested, this is a serious post by me. Good input by well meaning people is welcomed, encouraged. Open to discussion, positive discussion.
Jeff Medwin
Edits: 11/23/14Follow Ups:
The Heathkit W6M drives the output tubes with a pair of cathode followers, achieving essentially what you are saying, driving power tybe grids with a very low impedance. I have always seen that as a fantastic idea and would like to try it some day.
So far as this amplifier goes, I will add a little more filtering to the filament supply for the 2A3s, and maybe to the B+ too, beyond that I am calling it done, as I would like to concentrate my hobby expenditures (time and money) on building a WE91a replica (see post below). I think I also need some more efficient speakers!
These are nice drivers.
Have you actually heard these? on paper they look great... It's a shame the second page is included, with te $57/ea banana plugs, it makes me doubt if the speakers are worth their asking price, although going by specs and build quality they do look like a fair value.
I own the H21LB15 and the super tweeter. I stop thinking about speakers after I bought these yeas ago. YMMV.
Yes, as a by-product, Low Z drive ( from the anode, not from the cathode ) was there, but the REAL goal was 20K or less grid-to-ground 2A3 resistance.
I spotted a high resistance Finals grid-to-ground in Thorsten's regulated amp also, and I thought a grid choke would excel there too.
Pentodes sound best with a separate supply for G2, ala Paoli 60M. What everyone else does is too much of a compromise ...a drop down resistor and cap.
Speakers .....Altec is possibly the best bang for the buck. I am partial to 604 MLTLs because they are a point source, or, on a budget ( I am! ) A7-800s with their partial front horn load of the woofer. Fun to hear. Hard to lose value, almost an investment.
Jeff
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