807 E-Linear

[Bandersnatch]

Originally posted by arnoldc
Is this topology specifically made for plate loaded input tubes?

What if I have a CCS on the input tube plate? Will that make a difference?

Hey-Hey!!!,
The CCS will not allow the circuit to operate as intended. It takes advantage of the near zero PSRR of a pentode. A voltage is changed by varying the current through the first stage, and the tapped plate winding of the final takes some of that change back. Triodes don't yeild much FB, and even the difference between bypassing its cathode R makes a difference. I like cascodes, mostly because I build this circuit PP and use the input stage asthe PI too. No parallel path to the cathode like a pentode's g2 offers in the cascode.

In particular, I have tried the 6AU6 and like it much! Try a 30k plate load and a g2 voltage of ~100.
cheers,
Douglas

[EC8010]

Originally posted by Bandersnatch
It is indeed called E-Linear.

Any idea where the name came from?

[Tweeker]

The 04/05 AudioXpress had an article "A Single-Ended E-Linear Amplifier".

Some supplementary info and files from Pete Millet.

[pmillett]

'twas Douglas that coined the phrase...

Pete

[Fuling]

Initial measurement results (my tone generator is the crappiest thing I´ve ever seen so I will redo this once I get me a proper one):

Output power: 4W into 8 ohms, probably more if the tone generator had been able to deliver more signal...
Gain: Just over 2x from input to output. Painfully low I must say.
Frequency response seems to go past 40kHz, this will also be investigated further later on.

[Bandersnatch]

Hey-Hey!!!,
As you've probably seen in Pete's article, higher gm in the driver pentode is the Way to gain. gm x Rl eh? Anyway, I like the 6AU6 but the 12HL7 has done well with 6L6's...Take one of Pete's OP for that valve, perhaps with a 15k plate load? 20k maybe? g2 at 75-90V I think...

I did name it. E got chosen for a few reasons for setting this U-L based circuit apart. It is voltage FB on a gm device that makes it work so well.

One of my fave's is a triode-MOSFET cascode. No need to deliver g2 current at the equivalent node point of the upper gate. The plate lines are about horizontal as well...maximum FB.
cheers,
Douglas

[janneman]

Originally posted by Fuling
I agree with Circlotron, the 10 ohm resistor is in series with the primary winding rather than with the secondary winding.
It drops about 0,65VDC at idle and perhaps 1Vpp at max output power, a very small fraction of the total plate swing.

Ahh yes, I didn't catch that there actually was a transformer, I thought that this was a cathode follower type. My bad...

Jan Didden

[Fuling]

Triode-mosfet cascode seem interesting, I guess the existing ECC88 would be a good choice then?
The gain is way too low right now, we had to use an SS preamp to push the amp into clipping. I assume cascoding the input stage would increase gain, right?

[Bandersnatch]

Hey-Hey!!!,
The cascode is not a gain machine any moe than a pentode is. Depends on your plate load of course gm x plate load or there-abouts...

I think my primary attachment to the cascode is due to its horizontal plate lines and their effect on FB level. An ECC88 and a FQP1N60 MOSFET should work well. Put the gate where the upper grid would normally go.
cheers,
Douglas

[Fuling]

The cascode is not a gain machine any moe than a pentode is

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