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..
Fuling said:
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
Thanks, I think I´m 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.
Edit: Would E280F be a good pentode driver for this amp?
I happen to have a few.
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.
I was reading Pete's article yesterday and came upon this thread today.
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 I´m going to build a 12B4A preamp for my brother.
The overall gain is a bit low so I´m going to build a 12B4A preamp for my brother.
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?
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?
I didn´t calculate the gain, but according to my brother the gain is too low when he plays vinyl. OTOH, as he doesn´t 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...😀
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
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
so...how about using Alan Wright's 6dj8 cascode input, complete with CCS on the tail, in this topology?
pedroskova said:
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
Different taps
The Edcor OPTs that I use only have 43% taps which are connected to both g2 and the feedback.
The Edcor OPTs that I use only have 43% taps which are connected to both g2 and the feedback.
Hi Fuling,
Got a little curious of the E-Linear principle. Want to sim your original circuit to understand it better. Do you have the primary and secondary DCR of the Edcor?
Got a little curious of the E-Linear principle. Want to sim your original circuit to understand it better. Do you have the primary and secondary DCR of the Edcor?
Hi revintage, I can measure the DCR of the primary but the secondary is below 1R, which I can´t measuere accurately.
Hello,
I am building a PSE 807 amp & useing Hashimoto H 20-7u w/ 5 & 7k taps w/ UL taps for both. 5687 into O'netics 1-1 IT for coupling & adjustable fixed bias via 4- 20 turn 20k trimmers for the 807's. I would like to try the E-linear gig with it but do not uderstand the 8 ohm transformer below the 10 ohm series bias reading resistor on the original poster schemetic. Can someone explainthis to me .? Also can this e-linear be used with an IT as I plan to use..? I can try differant drivers, but wanted to try these tungsol 5687's I have on hand allready. If 5687 is no go, I have a box full of 6au6. That tranformer off the cathode is confusing this half asleep Joe
I am building a PSE 807 amp & useing Hashimoto H 20-7u w/ 5 & 7k taps w/ UL taps for both. 5687 into O'netics 1-1 IT for coupling & adjustable fixed bias via 4- 20 turn 20k trimmers for the 807's. I would like to try the E-linear gig with it but do not uderstand the 8 ohm transformer below the 10 ohm series bias reading resistor on the original poster schemetic. Can someone explainthis to me .? Also can this e-linear be used with an IT as I plan to use..? I can try differant drivers, but wanted to try these tungsol 5687's I have on hand allready. If 5687 is no go, I have a box full of 6au6. That tranformer off the cathode is confusing this half asleep Joe
hey-Hey!!!,
I'd recommend against the 5687; the low plate resistance will absorb most of the FB. I haven't seen a decent way to use an IT with the E-Linear circuit. I choose instead a grid choke on the finals and as low a plate resistor on the front stage as my gain requirements allow.
6AU6 is a fine one, and only slightly behind 6AC7 IME. The 8R coil below the cathode is the OPT's secondary, arranged for cathode FB( a nice touch I might add ).
As Bandersnatch say there is a NONO to use a triode driver, must be pentode when going "inverse feedback" or as in this case "partial feedback".
There are no big problems using an IT with this type of local feedback. Must have high primary inductance though. What is your O´netics?
There are 3 feedback-loops around the 807. Get rid of at least one! The cathode feedback will give some DC on your speakers so maybe that one should go first.
The transformers you have is not suitable for PSE as a single 807 shouldn´t be loaded higher than ca 5k. So go just SE.
There are no big problems using an IT with this type of local feedback. Must have high primary inductance though. What is your O´netics?
There are 3 feedback-loops around the 807. Get rid of at least one! The cathode feedback will give some DC on your speakers so maybe that one should go first.
The transformers you have is not suitable for PSE as a single 807 shouldn´t be loaded higher than ca 5k. So go just SE.
Did a few sims when I got home from work. The most promising is actually the classic Schade with added UL and triode driver! 6AU6A also worked OK but the low end resonance will be hard to tame.
I believe that instead of the two mixed loops of the E-linear it will be even better with separate plate-grid and std UL loops. Added the optional cathode feedback loop. Clipping will occur at 8-9W.
I believe that instead of the two mixed loops of the E-linear it will be even better with separate plate-grid and std UL loops. Added the optional cathode feedback loop. Clipping will occur at 8-9W.
Attachments
Thanks for the schematic.I will get the O'netics IT specs tommorrow when i get home & post them. I think I will just ground cathode or insert a 10ohm resistor for readings if possible with this schematic. I will for go the PSE & just go SE. L7 & R5 confuse me, is that L7 related to my OT secondary..? sorry for bieng not up to speed on this cathode loop. I really look forward to wiring this circuit up 7 will start with 5k.
thanks joe
thanks joe
Hey Joe,
The 807s can not take more than 300V Ug so you can not go UL. UL shouldn´t be needed if you adapt the Schade correct. Of course you can also skip the cathode feedback. Beware the sensitivity will be rather low with the 5687.
The 807s can not take more than 300V Ug so you can not go UL. UL shouldn´t be needed if you adapt the Schade correct. Of course you can also skip the cathode feedback. Beware the sensitivity will be rather low with the 5687.
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