Now for something different...

[swt61]

I'd use a monkey, some aluminum wire and two tubes of JB Weld.

[spritzer]

I think Steve nailed it!! Paging Dinny, paging Dinny to the Mafia DIY section...

[FrankCooter]

A reworked ESX would be a valuable addition to the stable of DIY electrostatic amps, but I think you're getting away from the original"Volksamp" concept, which, if I understood it right, was to build a small, cheap, easily understandable novice amp that didn't suck. Very few novice tube builders understand balanced inputs. Even fewer (including me ) are going to really understand what's going on with that cross-coupled first stage. Add features like fixed-bias, 4 gang volume pots, and pentode based CCS's, and you now have a very ambititious project. If you want balanced inputs ( I am not against balanced circuits per se despite whatever impressions I may have generated earlier), an ECC99 based BATE with a simplified power supply looks about as simple as you can get and still meet your design goals.

On a humorous note, I've actually seriously considered an electrostatic "spud". It's technically conceiveable using something like the 6HV5. With a 6dB input step-up, you can generate a gain of 600 and a 600V swing with pretty decent linearity. The Rp is too high for for a transformer, but if you choke loaded it and cap coupled the output to an autoformer, it looks like it would work. Major downside is that the 6HV5 needs about 1200V on the plate to do this. Not something to try at home.

Edited May 15, 2012 by FrankCooter

[wink]

There's nothing about 1200V which is anything resembling amusing, except , perhaps watching the incendiary silicon hit the fan.

I, for one, am all for it.....

[spritzer]

A ESX would be simpler to build than a BATE and the lack of capacitors would make all the crazy people out there happy. I like the ESX because it uses so few parts and while the whole cross coupled thing looks complicated, it really isn't in a way and people never need to know how it works. Well that and it sounds amazing once it is up and running properly.

The balanced inputs are "free" here and having guided dozens and dozens of people through amp builds they have never caused any issues. Not much difference between a dual pot and quad pot and steppers are cheap on ebay. The ESX amp circuit is cheap to build so only a few $ in resistors and tube sockets plus four 2$ caps and that's it. 10W plate resistors would be pretty expensive so a simple 10M90 CCS isn't that much more expensive with much better performance.

A spud... yeah let's class that with KG's gas tube amp...

[deepak]

What sort of power supply are we talking for the ESX, and does it use 4x EL34 on the output?

[spritzer]

I'm only talking about using the basic ESX circuit so the output tubes will be ECC99 with ECC81 drivers.

The psu will be something simple which does the job but follow the same lines as the latest stuff from Kevin. I like the idea of using a separate psu for the bias supply with it's own regulation and it would be easy enough to just add a couple of voltage divider spots onto the board for 230V and 500V output so no adjustment necessary. Since we are probably going to need a custom transformer then we can do pretty much anything from the simple N- and P-channel affair in the old KGSS article to a version of the BH psu with split secondaries. A delay line could be added but it just adds cost and really isn't needed.

[Beefy]

CCS it up, and the power supply requirements would drop a fair bit, wouldn't they?

[spritzer]

Yes and no. It will always be way over spec just to be safe.

[luvdunhill]

people never need to know how it works

i think this is a poor requirement for the pleb-amp, but that's just me.

[spritzer]

It has magic glowing shiny things which makes loud become moar loud?

[FrankCooter]

i think this is a poor requirement for the pleb-amp, but that's just me.

I agree. Most people who would want to build even the simplest electrostatic amp would want to be more than just "board stuffers". Building any amp should be an educational experience. I imagine a potential builder of this type of project is someone who's already built a cmoy, a spud, or maybe restored a Dynaco. They'll be interested in at least a conceptual understanding of the circuit.

So what's going on with the first two stages of the SRX? You really don't see very many cross-coupled circuits in tube audio. At first glance it looks like a Van Shoyoc differential amp, but unlike the Van Shoyoc circuit, the first tube pair are not cathode followers. So if the first tube pair are actually amplifiers, are the second pair simply some sort of active load, or are they amplifying too? Since the second pair have plate loads and the output signal is being pulled of the plate rather than the cathode, looks to me like some amplification is going on here too.

Edited May 17, 2012 by FrankCooter

[keithpgdrb]

I laughed at the description of the "potential builder", because thats basically me. cmoy, various repairs, and fisher tube amp restore. even though I have almost no F-ing idea what most of the things are that your referring to, I'm learning a few things by needing to look them up.

[kevin gilmore]

stax has always come up with unique circuits. The srx circuit is all about differential

gain usually from a single ended input. You have to model it in spice to see what

is going on, but there is voltage gain from both sections of the input amplifier.

Synthesis later when i have some time.

Front end is good for 45db of gain. If the output stage has 20 db of gain or more

and the closed loop is 60db, that leaves 5db for feedback. Something

mikhail clearly did not understand.

Edited May 17, 2012 by kevin gilmore

[luvdunhill]

Kevin, if you do model it, I'd be curious about the distortion and it's relative harmonic magnitudes.

[spritzer]

There was a brilliant piece I read about these less common tube circuits back when we were rebuilding the ES-1 but I can't find it now. It should be here somewhere but I have the annoying habit of just throwing everything in one folder and not sorting it...

I want everybody to be able to build it so focusing too much on how the circuit works might put some people off. Some basics are necessary (why you can't adjust the DC balance at the output etc.) but I still remember reading the KGSS article all those years ago and trying to gleam something useful from it in that wall of stage this and feedback that.... I also like the idea to have the boards fully self sufficient so one doesn't need the BOM or any documentation to finish building it. All the necessary info should be on the boards and no stupid vertically mounted parts.

[kevin gilmore]

http://gilmore.chem....ern.edu/srx.jpg

uses cheap current source.. Just 2 power supplies.

12 volt filaments for input and output stage. Need 2 seperated windings.

Same holes and size board as the bate.

power supply is the bate power supply with the C- supply not stuffed.

About as simple as one can get.

the current source really takes the distortion down a fair amount. To about .03% thd.

edit: birgir wants to do dc filament supplies.

That is next.

Edited May 28, 2012 by kevin gilmore

[spritzer]

I just ran the numbers and the parts cost is about 150$ for the amp section. Most of that are the teflon sockets and all the PSU bypass caps though.

[kevin gilmore]

So the stax mafia has been hard at work on many versions of simple tube amps.

Here is my favorite.

http://gilmore.chem....ern.edu/bae.jpg

birgir did not want to use the 6sl7 because of availibility issues, so this

uses the most common in production tubes.

6SN7 just do not make sense, they do not have enough gain.

Mikhail learned that first hand, someone else is about to learn the same

lesson soon. With not enough open loop gain, all sorts of issues including

much higher distortion, and channel balance issues...

Of course you really should do 10m90s current sources, lowers the distortion

a factor of 10.

And i don't think this can be crammed into one box.

DC coupled outputs.

i'm sure some people will want to use 6L6GC fatboys instead.

Edited June 8, 2012 by kevin gilmore

[chinsettawong]

So are they 12AX7 for the front tubes?

Wachara C.

[kevin gilmore]

Yep, just like it should be.

6sn7 is max gain of 20 (10 is reasonable for low distortion)

12ax7 is max gain of 100 (50 is reasonable for low distortion)

Edited June 8, 2012 by kevin gilmore

[flecom]

you need to stop making things I want to build

a compact inexpensive electrostatic tube amp? whaa?

[kevin gilmore]

It is certainly not compact. Unless you are comparing it to the DIY T2.

It's about half size. Amp Board is 10.5 x 6 maybe it will end up

A bit smaller.

The power supply board is bigger. 2 power transformers are required if you

Don't want to trash the output tubes.

[flecom]

thats pretty compact for a tube amp... at least the ones I have worked on! (although most of those have been for... "higher" frequencies (in the MHz) hehe

always wondered if an electrostat headphone amp like this could directly drive a martin logan panel... what say you wizard of the audible?

Edited June 8, 2012 by flecom

[kevin gilmore]

you wanna build one of these!

http://gilmore.chem.northwestern.edu/beveridge.jpg