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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

6S19 Circlotron (OTL)

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Zero Cool said:
I have TWO of Ralph Karsten's (Atma-Sphere) early prototype Circlotron amps!!! Both use 8 6AS7G tubes per channel.

l_a8318c528724f72e59a5ccf99d813468.jpg

ZC,

Which model amp is that on the picture?

BTW, I have been talking to Ralph about the upcoming OTL kits he plans to start selling again.

-- josé k.
 
After a few months of salmon fishing and RC flying I´m getting back on the DIY audio track again. Instead of finishing some of my half-built projects I feel it´s time to start working on the circlotron.
Due to the number of tubes and power supplies I will build it as mono blocks and to save a few hours I will "borrow" some chassis parts from an earlier OTL project that probably never will be finished.

I will employ John Broskies output stage topology (see link in the previous post) with 1x 6N6P and 8x 6C19 per channel plus another 6N6P as an LTP input/phase splitter.

http://www.mif.pg.gda.pl/homepages/frank/sheets/113/6/6S19P.pdf

http://www.tubes.ru/techinfo/HiFiAudio/6n6p.html

I´ve spent the evening cutting and drilling alu sheets for the chassis, they will be spray painted tomorrow and left to dry over the weekend before I do anything with them. The paint I´m using dries in a couple of hours but takes a few days to fully harden.
 
Hi reVintage!

That is pretty much what I have in mind, but there is one thing that doesn´t match Tubecads schematic:
R13/14 makes a voltage divider together with R1/3 which seems to cut the feedback signal down to ~25% of what it should be.
Remove R13/14 and increase R1/3 to 370R and see what happens...?

Thank you for "spajsing" this circuit for me!
 
This is how I would do it!

It was NOT ment to match Broskies schematic as it seems to be f-cked up! Must be a drawing error as I said in my previous post. Or also I could be the jerk, not to understand his strike of genius:clown:! Anyway I will give it another try tonight as I might have missed something. It could be as simple as that the gnd reference resistors are missing.

My circuit will not work changing R1/R3 as these sets the current through the 6N1Ps to 8mA. And you must have R13/14 as these are for GND reference.

I recommend using a low-mu tube like 6H30 to lower sensitivety.
 
Sorry, forget the part about increasing R1/3 to 370R. Tankevurpa:eek:
I still don´t see the point in R13/14 though, the output stage would still have ground reference through R1 and R3.
Of course I´m talking about shunting R13/14, not removing them!

Regarding the high sensitivity I´m going to use 6N6P (µ~20) in the input and driver stages.

The only weird thing I can see in Broskies circuit is the bias arrangement, I don´t understand the need for a -300V rail when the output tubes only needs something like -25V and cathode bias would be perfectly sufficient for the driver tubes.
 
I thought about using 6N1P at first but I prefer amps with low input sensitivity (and low feedback if possible).

Now I understand what you mean is wrong with the broskie circuit! He explains the need for ground reference in an earlier article about circlotrons so I guess he just left them out in this one to since the focus is on the feedback circuitry.
What I mean is that those reference resistors can do double duty as cathode (bias) resistors for the driver tubes.
The floating power supplies will then be raised a couple of volts above ground but as they are floating it shouldn´t matter.
 
Have spent the last hour trying to sim Broskies circuit with no success.

Anyway, my circuit(below) seems to work. The sim indicates a Zout under 3ohm and a sensitivity of ca 0,4V rms. Thought output before clipping should be higher as this is indicated in TCJ PP calculator. I get 3-4W into 8ohm. With less feedback, higher R13/14, Zout gets higher. 8mA through all 6N6s, 110mA through each 6C19.
 

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