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807 E-Linear

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B

Bandersnatch

Member
Joined 2003
Fuling said:


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, that´s what I have around at home.

Cheers,

Daniel
Click to expand...

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
 
B

Bandersnatch

Member
Joined 2003
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
 
B

Bandersnatch

Member
Joined 2003
pedroskova said:
so...how about using Alan Wright's 6dj8 cascode input, complete with CCS on the tail, in this topology?
Click to expand...

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
 
J

JandG

Member
Joined 2005
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
 
B

Bandersnatch

Member
Joined 2003
JandG said:
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
Click to expand...

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 ).
 
R

revintage

Member
Joined 2007
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.
 
R

revintage

Member
Joined 2007
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.
 

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J

JandG

Member
Joined 2005
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
 
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