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Old 9th January 2007, 10:09 PM   #21
arnoldc is offline arnoldc  Philippines
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hi douglas, thanks mucho for the explanation. this is a good read although i've seen pete's site and have a schematic on my hard disk for a long time. maybe this be be a good weekend project as i have 807s and UL transformers too..
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Old 9th January 2007, 11:14 PM   #22
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Quote:
Originally posted by Fuling


But perhaps more so than a resistor loaded triode with an unbypassed cathode resistor? I guess the cathode resistor decreases gm quite a bit?

I will try this out with IRF820 in the upper position, thatīs what I have around at home.

Cheers,

Daniel
The unbypassed resistor does drop the gm a bit. It increases Rp, which is probably the reason the bass performance got better. In the very high Rp that you'd find with a pentode or a cascode it gets even better. Do bypass the cathode R in that case...

The IRF820 is a nice one too in that position. If you want to try un-bypassed cathode R, ref the gate to the cathode, not ground...or at least try both( I suspect you'll like the cathode ref better ).
cheers,
Douglas
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Old 10th January 2007, 11:38 AM   #23
Fuling is offline Fuling  Sweden
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Thanks, I think Iīm getting a bit enlightened about this kind of feedback now!

Edit: Would E280F be a good pentode driver for this amp?
I happen to have a few.
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Old 19th February 2008, 07:08 PM   #24
JoshK is offline JoshK  Canada
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Did you ever get to try the triode/mosfet cascode? How did it fair?

I was reading Pete's article yesterday and came upon this thread today.
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Old 19th February 2008, 07:37 PM   #25
Fuling is offline Fuling  Sweden
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JoshK: No, I went for the E280F in pentode mode (with E-Linear feedback) and it was very successful.
The overall gain is a bit low so Iīm going to build a 12B4A preamp for my brother.
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Old 19th February 2008, 07:51 PM   #26
JoshK is offline JoshK  Canada
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thanks for the response.

Gain...the other thing that has me scratching my head. How do you calculate the gain from this amp? Or do you just observe the result when done?
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Old 19th February 2008, 08:23 PM   #27
Fuling is offline Fuling  Sweden
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I didnīt calculate the gain, but according to my brother the gain is too low when he plays vinyl. OTOH, as he doesnīt have any kind of preamp (not even a passive volume control) at the moment the sound is a bit too loud when he plays CDs...
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Old 19th February 2008, 10:03 PM   #28
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hey-Hey!!!,
I am glad to hear of your good results with the E-Linear amp circuit. Have you the ability to try different taps? I ask because a friend who I helped with his PP 807 amp finds it best with g2 on 40% and the front end on 20%. This with 10k a-a in the form of a Heyboer-wound S-265-Q
cheers,
Douglas
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Old 19th February 2008, 10:44 PM   #29
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so...how about using Alan Wright's 6dj8 cascode input, complete with CCS on the tail, in this topology?
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Old 20th February 2008, 12:18 AM   #30
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Quote:
Originally posted by pedroskova
so...how about using Alan Wright's 6dj8 cascode input, complete with CCS on the tail, in this topology?
IIRC, Allen references the upper grid to ground, and wastes a lot of B+ in the 'here be Monsters' part of the cascode's plate curves. Not good for circuits with Class A-capable B+.

Tune it up a little bit, and it'll be quite OK I think.
cheers,
Douglas
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