Chosing class A output transformer

simple class A low power< 15W that can drive 4, 8, or 16 ohms and has high linearity with a separate negative feedback coil(so switching load sizes does change the feedback path).

Would you please make up your mind:

a) a tube amplifier with an output transformer, or b) high linearity.

simple class A low power< 15W that can drive 4, 8, or 16 ohms and has high linearity with a separate negative feedback coil(so switching load sizes does change the feedback path).

simple class A low power < 15W that can drive 4, 8, or 16 ohms and has high linearity with a separate negative feedback coil(so switching load sizes does change the feedback path).

ld a simple class A low power < 15W that can drive 4, 8, or 16 ohms and has= high linearity with a separate negative feedback coil(so switching load si= zes does change the feedback path).

Any of the common(i.e., cheap) standard tube amp tubes. 6L6, 6V6, EL34, etc= ...=20

I could go with a standard class A output transformer replacement but looki= ng for a some theory so I don't end up with a doozie.

Also, I'm looking for some transformers for coupling. Need a good linear hi= gh mu audio transformer(something that has good flat response in the audio = range) that is not too terribly expensive.

"Archival" John Fields wrote: Archival

Any of the common(i.e., cheap) standard tube amp tubes. 6L6, 6V6, EL34, etc...

I could go with a standard class A output transformer replacement but looking for a some theory so I don't end up with a doozie.

You thinking of SET or pentode mode ?

Also, I'm looking for some transformers for coupling. Need a good linear high mu audio transformer(something that has good flat response in the audio range) that is not too terribly expensive.

.... Phil

d a simple class A low power < 15W that can drive 4, 8, or 16 ohms and has = high linearity with a separate negative feedback coil(so switching load siz= es does change the feedback path).

transformers in audio amps are so 70s

simple class A low power< 15W that can drive 4, 8, or 16 ohms and has high linearity with a separate negative feedback coil(so switching load sizes does change the feedback path).

Experience. I've building electronics since 1960's, and the only viable active components were tubes, at the beginning.

"HardySpicer"

Coupling and output transformers were eliminated from nearly all transistor amps in the mid 60s.

Only place they lingered on for a while was in portable radios and loud hailers that used Germanium devices.

Of course, 70V and 100V line amplifiers still mostly use output transformers.

... Phil

simple class A low power < 15W that can drive 4, 8, or 16 ohms and has high linearity with a separate negative feedback coil(so switching load sizes does change the feedback path).

for a some theory so I don't end up with a doozie.

mu audio transformer(something that has good flat response in the audio range) that is not too terribly expensive.

Single ended or push-pull ?

If single ended, please remember to use the air gap in the core to avoid any DC current saturation issues.

feedback path).

Apart from safety issues (especially in AC/DC receivers), what is the need for a separate feedback winding ?

The amplifier open loop output impedance must be huge, if using the transformer secondary as the feedback winding with some unspecified load, would make any difference.

feedback path).

My first audio amplifier was a DS-501 direct driving a speaker in parallel with a big-ass choke... ~6W out into 8 Ohms, running on a car battery :-) ...Jim Thompson

And enough leakage current to self bias. :(

The only transistor course I had at MIT was in regard to biasing Germanium. ...Jim Thompson

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Germanium transistors are the liberals of the semiconductor family. Fortunately there aren't many left. ;-)

Slow, leaky, can't take the heat, tend to run away?

Why is SiGe better than Si?

Best regards, Spehro Pefhany

No idea. I've never worked with them.

Much higher mobility, both electrons and holes, so for a given device size you get lower extrinsic base resistance. Plus you can do interesting strained-layer things, plus the heterojunction makes the built-in field in the CB region larger, which reduces the Early effect amazingly. The spice models for SiGe devices like the BFP640 all say VAF=1000, which is probably an underestimate. Some of them actually show a negative collector resistance in the datasheet curves, which I strongly suspect is thermal rather than electronic in origin.

(I just started using them myself in the last 6 months, and have been reading up on them. I dropped my graduate solid state class halfway through, when my first daughter was born. I had to do a bit of academic triage, and it looked like the one it would be easiest to pick up on my own afterwards. Still working on that.)

Cheers

Phil Hobbs

SiGe is an EMITTER implant in an otherwise Silicon-only process. It results in dramatically higher fT. ...Jim Thompson

Are there any good tutorials / books for designing toroidal transformers for audio use ?

My searching has found companies that will design one for me.

I would like to know the design parameters I need to use before I search out a manufacture.

Thanks

hamilton