Simple valve power stage

That implies you are working into an impedance of about 500 ohms. (200 V pp = 70 V rms.)

Tube audio amplifiers normally use an output transformer. (Your impedance of 500 ohms is appreciably less than the plate impedance of a tube.) To avoid it, you might use a cathode follower. Why are you averse to including a transformer? Also, what is the input signal amplitude?

There are a few valve (tube) fanatics on alt.binaries.schematics.electronic who would be able to sketch up what you want, and since its an alt.binaries group - they can post the schematic too!

Are you sure you want to do this ? A Class A stage without output transformer can only acheive a theoretical max efficiency of 25% IIRC which means you'll have 10W in the load and 30W dissipation in the outout tube(s) !

Push-pull makes far more sense even at this lowish power.

Graham

Not that push-pull isn't a better idea...

A quick web search on got me over a million hits, many of which were for building projects. Probably anything that uses as single-ended 6L6 or similar can be used by taking the output off the plate with a great big blocking cap.

You can get an RCA tube manual from

transformer

I know it's 50% for transformer but choke too ? Not sure how that would work over a range of frequencies. I suppose Zchoke simply has to be >> RL ?

That's what I had in mind.

I think so. But that compels use of a transformer !

This would be better done with some high voltage transistors really and a complementary emitter follower output stage. 200V isn't really a big deal.

Graham

But re-reading his post, why would he want to use tubes if he wants 'audiophile quality' ? Maybe he wants audiophool quality ?

Graham

He says, "I am NOT looking for audiophile quality."

...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

If I was going to do something like this I'd use the video amplifier on the CRT base panel from a scrap PC monitor, modern hi-res monitors have a BW DC to over 200MHz. The input is a fairly straightforward common emitter stage, the common base section of the cascode amplifier gives it a large voltage gain and the complementary emitter-follower output stage gives it good power gain (but I'm not sure if its as high as the OP's requirement!) - but then as I used to service PC monitors, I have some spares stock of CRT boards left over.

What does that have to do with anything? RP ~= 35K. So treat it as a current source.

Eh? What would that buy you?

Aside: When I was a junior in college I proved that driving 50 ohms worked better driven from the plate rather than the cathode (of a pentode ;-)

...Jim Thompson

'audiophile

LOL ! That's the trouble with scanning quickly. Even less 'sense' in using tubes.

Graham

Efficiency ?

A power tube plate will be a lot lower than 35k.

A simple circuit.

Graham

Class-A is class-A.

Directly obtained from the 6L6 data sheet. I'm an old fart... I have multiple tube manuals... built my first audiophool stuff with tubes ;-)

Cathode followers at high swing aren't terribly linear.

Me, since it's high voltage and significant power...

I'd use the 6L6 with a transistor in the cathode path to make a VERY linear device ;-)

...Jim Thompson