Now for something different...

[spritzer]

These amps are designed for the ca. 120pf load presented by a Stax driver but some can drive tougher loads such as the Floats but I wouldn't venture any higher than that. The voltages we are working with are also miniscule compared to the drive voltages inside an ESL.

We have been prolific for the last few weeks discussing new designs and how to rework old ones, amps and power supplies alike. Who needs sleep anyway...

Given this is where it all started, the B-10 will probably see the light of day this weekend (barring any late cake orders...). The amp section has been ready for weeks but Edcor took their sweet time with the transformers. Massive distortion here I come but it will be as good as this circuit can be made.

[chinsettawong]

Hi Kevin,

Could you kindly post the schematic diagram of this new amp? Hardwiring this amp shouldn't be that much work.

Wachara C.

Edited June 9, 2012 by chinsettawong

[kevin gilmore]

http://gilmore.chem.northwestern.edu/bae.pdf

[spritzer]

What's missing from the schematic would be the wattage of the EL34 cathode resistors. While all the other resistors are 1/2W these need to be larger.

[kevin gilmore]

100 ohm 2 to 5 watts

[justin]

call it the YES

[keithpgdrb]

The B10 isn't the bate is it? I just got confused. Maybe I'll ease off the beer for the next hour.

[spritzer]

The BATE is pretty much what we have in the schematic above. Parts of GES, parts of the ESX all mixed in together.

The B-10 is my take on the RSA A-10 so improved and made safe but the basic circuitry is still the same. Looks something like this:

[Knuckledragger]

^^ I think you've really captured the, uh, spirit of Ray's designs there. The only major flaw I see is that your logo is not sufficiently large nor arm-gnawingly ugly.

[Victor Chew]

Quite a bit of disussions in various directions until the design is finalised, so not surprisingly, confusions can be caused. However thats just normal.

Thats a nice build Birgir. How does it perform?

Edited June 10, 2012 by Victor Chew

[keithpgdrb]

Ok. So is this bate the poor mans stat amp you've been talking about? Or is the poor mans a separate project? I'm following as best I can.

[wink]

How about the "Cheap and Cheerful"?

[spritzer]

^^ I think you've really captured the, uh, spirit of Ray's designs there. The only major flaw I see is that your logo is not sufficiently large nor arm-gnawingly ugly.

I clearly need to add some gold paint then....

[FrankCooter]

Lots of interesting and informative work going on in a still relatively underexplored area of tube application.

So far, at least on paper, the circuit that interests me most (and I understand the least) is the modified SRX circuit. Still don't fully understand the cross-coupling and the ultra-low voltages on the 12AT7 plates. If I build this, I'd like to with 6BL7 instead of ECC99 outputs, use a C- bias supply, and run the HV rails at 400V. Any reason not to up the 12AT7 stack to the full HV rail if the output bias is now handled by a C- supply? If it's not to much trouble, I'd appreciate you posting a schematic.

I'm a bit puzzled why you didn't use a voltage divider off the negative HV rail to offset the operating point of the first stage of the BATE and the El34 amp. Seems like this would have been a good way to eliminate the input cap and perhaps enable direct coupling between the first and second stages. Also wonder why you went with the 12AX7 instad of the 12AT7.

[kevin gilmore]

I have been thinking of adding a resistor string to the -HV line. But really i would like to add yet another

power supply, say -30 volts, and do a current source instead. No reason to have more capacitors in

the signal path if they are not necessary. Could use the input filament supply doubled and inverted.

More on the srx circuit later.

Also thinking of adding an opto coupled servo to the output stage. That gives me the excuse to

add 2 more power supplies.

Edited June 11, 2012 by kevin gilmore

[kevin gilmore]

so its been over a month since andy has built an amplifier, and the stax mafia needs to keep the guy busy.

So here is the bae. I changed the front end with a current source, and its dc coupled input and dc coupled output.

2 caps in the signal path.

http://gilmore.chem....ern.edu/bea.pdf

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

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

The power supply has a + and - 15 supply, because later i will probably add the servo

but at the moment with virtually all of the good opto isolator parts no longer in production, the

ones i would use are way over priced. And the test version oscillates very nicely at about 2

volts on the output of 2 hz. So that needs more work.

Next up what we are now calling the 2B10.

only one cap in the signal path.

Paralleled 5687's and DC coupled outputs with the above power supply set for +/-300

A total of 8 5687's. 6 seperate filament supplies...

I'll also be doing a new version of the kgsshv power supply with the added 60 volt supply to make

a high end, and universal power supply.

Edited June 13, 2012 by kevin gilmore

[spritzer]

The B-10 was a semi difficult birth over the last few days though most of the issues were linked to the new "super simple PSU" I drew up for the amp. Nothing wrong with the basic design, I just made too many layout mistakes but it's all good now. The only issue with the amp was tracking down the source for very faint hum. I did succeed in finding it and now it's as quiet as a solid state amp. Not bad for a cramped 1U chassis, shared umbilical cable and very hungry tubes (roughly 4A for the 5687's).

My only real goal with the amp was to see how hard I could push the tubes without them either imploding or the plates catching fire. The max rating for 5687's is 4.5W per triode or 7.2W for the both of them. Even at 9W for each envelope I had no issues but I backed off to 6.9W or so as these ratings really shouldn't be exceeded in a long term setup. As it stands now the B-10 is identical to the A-10 except where part changes made sense and naturally it's fitted with a much better power supply. Here is a list of the major changes:

-Volume pot moved so it's in front of the first stage, not after it as in the A-10. I added 500K grid resistors on the "lower" 5687 triode instead of the pot. I don't need to fool myself that this amp is noiseless even though it really is. Dead silent even at full volume with the super sensitive SR-003.

-Separate filament winding just for the 5687's which has the center tap connected to the +300V line through a 100K resistor. This is a major change since the A-10 uses two parallel connected switching supplies to run everything, tube filaments, relays etc. with the - side grounded. With one cathode in the envelope sitting way above the cathode-heater level this is downright dangerous so a floating winding referenced at +300V gives me trouble free operation for most of the output. Only at full voltage swing will I run into issues so it's not perfect but a huge improvement.

-The front end it fed of a fully regulated DC supply using it's own transformer. This also drives the LED's and is a large factor in the zero hum.

-Some modifications were made to the circuit so it sees a more stable load and thus behaves more like a SRPP circuit should. Ideally they should see a fixed load to behave but electrostatics are anything but that so a bit of counter balance was added.

Despite all of this it is not a very good little amp. Bass is lifeless and flat, top end uneven at best and all those lovely distortion molecules... It didn't like a loud session with some metal one bit either, audibly clipping into a Lambda Signature... Still, one could do worse for the 500$ or so this cost me to build. One could have paid Ray 6.5K$ for one which is even worse...

[keithpgdrb]

Oh man, ouch.

[kevin gilmore]

And this is the right way to do it.

And its constant current, not srpp!

http://gilmore.chem.....edu/srxa10.jpg

dc coupled input, dc coupled and self balancing output

one cap in the signal path. 10db of feedback, 54db gain

and a thd of about .2% max at 20khz

Edited June 14, 2012 by kevin gilmore

[decoherent]

... now my ears are sticking out:-) Electronics Schematics are still my favorite. Will yo be willing to publish those?

are we talking about close to 1kv ptp output with 2 V input signal?

Thanks.

[kevin gilmore]

We always do the schematics last after the prototype is working.

http://gilmore.chem.northwestern.edu/srxa10.pdf

more than 1kv peak to peak stator to stator with .6 volt rms input signal.

[decoherent]

Thanks Kevin.

The first stage is interesting indeed. I've never seen such a ccs (that doesn't want to make a statement of any sort of course). How the CCS works? Is its connection crossed between phases to balance the two outputs?

Thanks.

[decoherent]

... or you are referring to the tail side only being ccsed? Sorry for the obviously dummy questions.

Thanks.

[kevin gilmore]

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.

Edited June 15, 2012 by kevin gilmore

[spritzer]

We do have trouble doing something simple. Adding more parts, stages and power supplies is often just the most simple solution...