807 E-Linear

[Fuling]

The Edcor OPTs that I use only have 43% taps which are connected to both g2 and the feedback.

[revintage]

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?

[Fuling]

Hi revintage, I can measure the DCR of the primary but the secondary is below 1R, which I can´t measuere accurately.

[JandG]

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

[Bandersnatch]

Originally Posted by JandG

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

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 ).

[revintage]

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.

[revintage]

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.

[JandG]

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

[revintage]

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.

[revintage]

You can go UL if do like Fuling did, with a B+ of ca 300V.