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Old 23rd November 2002, 08:03 AM   #1
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Default comment on this design, please.

I'm looking for a good hybrid tube/mosfet design for my next project which will be my first tube-related work. This might be an obscure question, but... Is the following circuit a good design? I would think so because it's from the famous Welborne Labs. Just want to know what experts like you think about this. Anybody has done a diy version of this? Any comment is welcome. Thanks.

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R2 R7 R22 R27-------------100R 1/2W
R3 R23--------------------330K 1/2W
R4 R24--------------------1K 1/2W
R5 R10 R25 R30-------------221K 1/2W
R6 R26---------------------10M 1/2W
R8 R28---------------------33K 2W
R9 R29---------------------6K8 1/2W
R11 R31--------------------1M 1/2W
R13 R33--------------------750R
R12 R32--------------------2K74 1/2W

C1 C10---------------------0.022UF/400V film
C2 C12---------------------0.01UF/400V film
C3 C13---------------------1UF/200V film
C4 C14---------------------0.1UF/400V film
C5 C15---------------------68UF/400V electrolytic
C6 C8 C16 C18--------------2200UF/20V electrolytic
C7 C17---------------------100UF/50V electrolytic

D1 D2 D3 D4 D5 D6-----------100V/1A rectifying
Z1 Z2-----------------------12V/1W Zener (1N4742)
Q1 Q2-----------------------MOS FET (IRF710)
U1 U2-----------------------variable voltage regulator (LT1085CT)
V1 V2-----------------------vacuum tube (12AU7, 6DJ8 or 6FQ7)
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Old 23rd November 2002, 08:21 AM   #2
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Alan Kimmel is a knowledable and telented designer, so you could do a lot worse, and there should be few if any bugs in the circuit. I use current source loaded designs myself, and find them better than resistive loaded by quite a margin, and over choke or transformer loaded by a significant but much lesser degree (assuming quality iron).

I wouldn't bother with paralleling the tubes, but that's my preference, and I would choose them in the reverse order of the way you listed them, ie 6FQ7 first, providing the higher output Z isn't an issue. If it is, then the 6DJ8 would be my choice, and I'd substitute a 6H30 or ECC99 for any of them in an instant (circuit tweaked to suit).

I dunno if it mentions it wherever you got the article from, but the IRF710 might need to be heatsinked.

Go ahead, build it and enjoy. Let us know your impressions of it when it's done.

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Old 24th November 2002, 06:21 PM   #3
SY is offline SY  United States
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"Too many notes."
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Old 24th November 2002, 10:01 PM   #4
ststone is offline ststone  United States
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I don't see the hybride part of this design
some links

hawk, audiotechniek, John van der Sluis
look at the A18
alleen vragen
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Old 24th November 2002, 10:04 PM   #5
ststone is offline ststone  United States
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Default Kimmel is the (mu follower) man


Now for FETS I am still voting for NELSON
alleen vragen
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Old 24th November 2002, 10:35 PM   #6
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Default Go here for CCS mosfet designs

This guy has really been pounding the solder fumes lately on this sort of topology

Robert Morin
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Old 24th November 2002, 10:45 PM   #7
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Default CCS.


And if you want stay local Mr.Pimm commented right here:

Do I have this CCS configured correctly? Tube preamp..

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