• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6S19 Circlotron (OTL)

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Zero Cool said:
I have TWO of Ralph Karsten's (Atma-Sphere) early prototype Circlotron amps!!! Both use 8 6AS7G tubes per channel.



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.



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.


  • fuling.png
    63 KB · Views: 690
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.