EF80 / KT77 SIngle Ended

[costis_n]

Thought I'd leave that here.

Some cap values are to be discussed. Transformers and chokes ordered.

Thoughts?

[toprepairman]

Ditch the EF80's and use ECC81 or ECC83 instead, otherwise it'll be OK.
Henry

[Yvesm]

Or drop one EF80 and tie the remaining in true penthode

Yves.

[costis_n]

Originally Posted by toprepairman

Ditch the EF80's and use ECC81 or ECC83 instead, otherwise it'll be OK.
Henry

Any reasoning for that?

Originally Posted by Yvesm

Or drop one EF80 and tie the remaining in true penthode

Yves.

Ummmm, it's supposed to be a constant current draw stage. Note how the load resistors match.

[revintage]

EF80 looks acceptable when triode-strapped. Tom Schlangen has the curves. Going for ECC81 would probably degrade, ECC83 shouldn´t be mentioned as driver .

constant current draw stage

Would that make things sound better?

If going EF80 pentode you should also go Schade.

[Yvesm]

Originally Posted by revintage

. . .
If going EF80 pentode you should also go Schade.

Do you suggest using the KT77 in Shaded penthode mode ?
I would agree with that !

[costis_n]

Originally Posted by revintage

EF80 looks acceptable when triode-strapped. Tom Schlangen has the curves. Going for ECC81 would probably degrade, ECC83 shouldn´t be mentioned as driver .



Would that make things sound better?

If going EF80 pentode you should also go Schade.

It will. CCDA: constant-current-draw amplifier

I thought about Schade, but the extra regulator required is too complex for my feeble mind. And the power is enough as is. Actually, I was expecting a discussion about operating points etc. I forgot to draw the primary impedance of the O/P transformer, it's 4.5KΩ

[revintage]

Originally Posted by costis_n

It will. CCDA: constant-current-draw amplifier

So just because of Broskie did it, it will sound good?

Add a DC-connected CF if you want to go A2.

[Knarf]

Originally Posted by costis_n

It will. CCDA: constant-current-draw amplifier

Try redoing his math while you assume the internal resistance of your 'perfect' triodes has changed just 10% due to aging or normal parameter spread, like for instance Ri = 11K. Now your currents are suddenly off more than 10%. This will be worse still if the tubes were not perfectly matched to begin with, or if they drift apart as time passes (which they probably will).

Good tube schematics will consider tube imbalances and aging as a natural part of the design specifications. A design needs to be able to adjust gracefully for tube aging, whether manually or automatically.

Anything else is just a complete waste of perfectly good tubes IMHO, when people try to achieve perfect balance from their 'bad' tubes over time. TANSTAAFL.

The schematic may work perfectly for your application, but current balance is not something I'd consider a goal or a design parameter for the configuration.

Many of the modern 'perfect' tube designs seems to suffer from this lack of foresight, unfortunately.

- Frank.

[costis_n]

Originally Posted by revintage

So just because of Broskie did it, it will sound good?

Add a DC-connected CF if you want to go A2.

No interest in A2, seems a waste of effort, if you look at the curves. I am not an engineer, i just try to make something based off what i have read. I'm like people telling me to go Shade, because it seems to be trendy in here.

Even if it does not balance perfectly (what's perfect, anyway), is it not a good idea, to have a grounded cathode, then a cathode follower to drive the final?