Suggestions for Tube Amplifier

[Rundmaus]

Hi,

this is my first post in the Diyaudio forum, and I'd like to ask you for a little brainstorming . I'm not totally new in this hobby, already built the Zen Amp an the Bride of Zen preamp, and a pair of transmission line speakers. But my experiences with tube technology are up to now only repairing vintage radios from the fifties or so.

A few weeks ago I got hold of the AudioValve PCL805 headphone amplifier, and now i seem to be infected with the tube virus ...

Well, here are my rough ideas, i would like to hear your suggestions, if possible accompanied by schematics ...

- PP-Design operating in Class A

- Triode output stage

- "common" tubes, please no "exotics" which are difficult to replace

- 10 to 20 watts output power per channel

- "common" output transformer, something i can buy instead of building it myself

- and, i would like to do completely without semiconductors, so i need a rectifier tube vor the anode voltage, and AC heating for all tubes

Well, i'm looking forward to your suggestions, and sorry for my English

Greetings,
Andreas

[Bas Horneman]

Something PP EL34 or PP EL84 comes to mind.
Here is a good start for a schematic.

sorry...has semiconductors in there...but....


Plenty of choice for standard output transformers.

What preamplifier do you have? (Bride of Zen? what is the gain of that preamp?) What speakers do you have? How big is your room?

Regards,
Bas


ps..your english is perfect.

[Bas Horneman]

Another one

http://audiotropic.netfirms.com/Projects/mmAudio.html

[Rundmaus]

Hi Bas,

no separate Preamp, so a preamp stage needs to be included, in german its called a "Vollverstärker" but I can't remember the english word for this.

Speakers are selfmade transmission lines, should make about 90dB...

As stated before, I have absolutely no experience in designing tube circuits, up to now only repaired or upgraded existing ones... So I would be glad if, after some discussion, this thread might give some reliable, practically tested schematics. I think i know the basics about tubes and operation modes, but I shurely do not have the experience to turn a "standard layout" or principle into a well working amplifier. Just don't know the "dirty tricks" ...

One thing I forgot in my list above:

- I don't want to say that I dislike the "typical" tube sound, absolutely not! But in my opinion an amplifier should also have measurable qualities. A frequency response of about 25Hz-20kHz or better should be possible, and THD should be reasonably low...


Many expectations, I know, hope it isn't tooo much

Greetings
Andreas

[Bas Horneman]

Oeps ....both schematics I posted need a seperate preamp

[EDIT]...looks like Poinz's amp need not have a seperate preamp.

Many expectations, I know, hope it isn't tooo much

Not at all too much....very do-able.

[Brett]

Originally posted by Rundmaus
Hi Bas,

no separate Preamp, so a preamp stage needs to be included, in german its called a "Vollverstärker" but I can't remember the english word for this.

Speakers are selfmade transmission lines, should make about 90dB...

As stated before, I have absolutely no experience in designing tube circuits, up to now only repaired or upgraded existing ones... So I would be glad if, after some discussion, this thread might give some reliable, practically tested schematics. I think i know the basics about tubes and operation modes, but I shurely do not have the experience to turn a "standard layout" or principle into a well working amplifier. Just don't know the "dirty tricks" ...

One thing I forgot in my list above:

- I don't want to say that I dislike the "typical" tube sound, absolutely not! But in my opinion an amplifier should also have measurable qualities. A frequency response of about 25Hz-20kHz or better should be possible, and THD should be reasonably low...


Many expectations, I know, hope it isn't tooo much

Greetings
Andreas

I've built both circuits Bas has linked, and a few variations on each. The Wright PP1C is the better sounding of the two and is in your 10-20W spec. Mine are in storage, but iirc they were driven quite well with a standard CDP output even into less sensitive speakers then my horns. You could always build them and add a pre later, if you think it's neccessary. Use the specified Lundahl iron for them and a good PS as the cascode front end has a poorish PSRR.

Been thinking about a 6550 version (with proper chasis' this time) to drive my KEF 104/2's. I have all the parts here, but little time at the moment....

[Jaap]

For a first start a ecl82 push pull amp could be a good choice. But I suppose the Allen Wright amp is soundswize better.

Question: Why the Lundahl iron ?
Suggestion: the AW amp with 807 tubes.

[Jaap]

Your countryman Huber had an interesting EL84 on the web (now disappeared (?)).
Could anybody comment on this design ?
Did anybody build or heard it ?

[Brett]

Originally posted by Jaap
Question: Why the Lundahl iron ?

Because it's good, available, sensibly priced and what the designer recommends.

Suggestion: the AW amp with 807 tubes.

Probably be quite nice, but won't get 10+W in class A

[Jaap]

I thought that your suggestion had to do with something Allen Wright said on the tube asylum:

"In my experience, P-P amps need the standing current in the OP tubes to be VERY closely matched - or you will have a DC component in the OPT that really limits the fine detail µdynamics of the whole amp and causes it to sound closed down and lost.

Some OPTs are more sensitive to this than others: toroidals are the worst and cannot accept more than a mA before losing quality bigtime - 'normal' (non airgapped) P-P OPTs should be balanced to a mA if possible to be at their best, but Lundahls (which have a airgap even in their P-P OPTs) can be off a couple of mA without any noticiable loss."

It is not a secret that Allen has his PP-1c amp updated with a ccs under the cathodes of the outputtubes. In this way the outputstage is perfectly balanced and I think there is not a specific need for a Lundahl. You could easly use a famous vintage opt I suppose, or a cheaper one from Asia, or whatever quality-opt from own neighbourhood.