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spritzer
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paralled, yes. srpp, definitely not. srpp takes the output from the top cathode

and is bad when driving electrostatic loads because of the huge change in

impedance over frequency. This takes the output from the plate of the bottom

tube. So its a tube driven constant current source. Substantial difference.

The reason its doubled up is the cathode to filament voltage limits. No other

way to do this with a 5687.

Unless you are mikhail and can magically have a filament voltage at both ground

and -400 volts at the same time...

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paralled, yes. srpp, definitely not. srpp takes the output from the top cathode

and is bad when driving electrostatic loads because of the huge change in

impedance over frequency. This takes the output from the plate of the bottom

tube. So its a tube driven constant current source. Substantial difference.

The four 5687 tubes are configured in a SRPP topology, each tube drives one phase of the signal. -A10

wasn't it determined that amp isnt actually SRPP? that's a new one. Advertise something that's bad, when it isn't even made that way…lol

Edited by justin
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The latest pictures that were acquired prove that the A10 was in fact wired as srpp.

Very hard to determine from the low quality layout.

Broskie will argue that due to the load, it cannot possibly be srpp.

With very little additional work, this is easy to turn into a super B52, with

dc coupled outputs. (+/-125 volt power supplies)

(needs a servo to be safe)

birgir has decided to tackle this piece of shit next.

a full channel on one board including power supply. 5.1 x 3.85 inches

http://gilmore.chem....du/dorkstar.jpg

Edited by kevin gilmore
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What can I say, I'm a glutton for punishment. unsure.png Plus it's what, 300$ in parts plus chassis? Not a whole lot...

As for the SRPP, Ray has said many times that the amp is indeed SRPP and it is wired for SRPP. As Kevin said, Broskie would not agree though as the circuit will not behave as SRPP with an electrostatic driver as the load. We countered this by placing 1M resistors to ground after the output caps which will diminish the impact of the wild impedance swings. Not a perfect solution though.

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The input section is the stax srx circuit. Which is easy to model, but is hard to explain.

And it works and works well. The output stage is a tube constant current source.

It would be easy to do the same thing to the bae, which would result in a total

of 8 output tubes. The feedback is important and reduces what would be 3% THD

to less than .2% THD.

At some point these things start looking like, and are the size of the VTL WOTAN.

The power supplies get to be very large.

Kevin, what are the advantages of the srx input stage? How do you calculate gain and input/output impedance? Will two ccs in place of R1 and R6 make possible to avoid the global feedback?

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The advantages are more gain and one less capacitor. Trust me, you want the feedback, otherwise it sounds

like crap. This is the one that will probably make it to production.

http://gilmore.chem....rn.edu/beac.jpg

Its 10.8 x 9.2 inches

7 x 6.3v filament supplies.

I could split out the front end power supply, then you could run +/-500V for the output stage.

The nice thing about this one is auto balance output. In fact you could act like that knucklehead

in israel, and swap output tubes with the power on. And no nasty silicon to go up in smoke.

Edited by kevin gilmore
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The advantages are more gain and one less capacitor. Trust me, you want the feedback, otherwise it sounds

like crap. This is the one that will probably make it to production.

http://gilmore.chem....rn.edu/beac.jpg

Its 10.8 x 9.2 inches

7 x 6.3v filament supplies.

Crazy idea but with all that extra space to the sides of the input stage, it would be really sweet to somehow throw in the KG attenuator. That way the amp box could be one of the small compact Hifi2000 1U case like these.

Edited by Horio
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Except that the attenuator is a 6 layer board which would force the rest of

It to also be a 6 layer board and that is a bunch more money.

Probably enough room to add the mounting holes for a pair of them.

The 1u chassis is impossible due to the height of the caps.

Maybe if you lay the caps down. Also the electrolytics are too big,

And the attenuator is 1 inch thick

Edited by kevin gilmore
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Did some googling and this is what was said - EL34 and 6CA7 are similar. Both, are interchangeable without circuit mods. EL34 are British and the other American. Some have said that the EL34 sounds warmer whilst the 6CA7 harder with more top and bottom.

Does this mean that we can use EL34 as an option as well?

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all of these, roll forever

shortest distance socket to socket is 2.3 inches

i can make the board bigger if it needs to.

6L6G (and A,B,C versions)

5881

5932

7027

EL34

6CA7

KT77

WE350B

Compatible with an adapter

6550

KT88

KT90

Compatible with stupid adapter

EL360,3D21 and every other thing mikhail made for the esx

Edited by kevin gilmore
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We need to make one for the KT120 biased at half power... grin.gif I do think that the EL34 is the best bet and there are no triodes which can handle these voltages and don't cost a bundle. DHT's also bring even more filament hassle and multiplies the cost.

The 6CA7 was an attempt to make the EL34 without paying royalty fees to Mullard. They are pretty much the same.

I am indeed out of the Alpha pots but I might do another run. Too busy to even think about that now...

What's been going on lately is that we are looking at pretty much every possible way to design a Stax tube amp and designing circuit boards so people can actually build them. The board files will be made available so these amps can be built by anyone.

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