EL509 OTL for high impedance speaker array

[Mikael Abdellah]

I think I would like to try and build a OTL amp based on EL509, but I would like to run a single tube and construct a large array of high impedance speakers to achieve a suitable impedance for the output tube without using parallel tubes. What would be a good impedance for a EL509 or similar tube? I was thinking just above 3kOhm. How do I calculate and decide working parameters? Desired frequency range is roughly 250Hz-16kHz so this is no attempt to build the ultimate OTL amplifier capable of driving everything, I just want to satisfy my curiosity and build another tube amp

 

[artosalo]

As a Circlotron some 500 to 1k would be fine.
I have built - not an OTL - but Circlotron(s) with 1k load and two JJ EL509.
With 480 V +Ub the output is 100 W with less than 1% THD and no GNFB.

 

[Mikael Abdellah]

Thank you artosalo. I think I will keep it simple and just use a single tube. The circlotron looked a bit more advanced than I was aiming for. Also, I don't need that much power. I would be happy with a bit over 10W which shouldn't be a problem with a EL509.

 

[tubetvr]

I did my first OTL test with the circuit described by Philips for EL86, I didn't use EL 86 but some other tubes that I had including PL509, (0.3A series heater version of EL509). The result was so good that I continued to develop OTLs. This schematic is simple and use 2 tubes but it is not 100% balanced and give a lot of 2nd order distortion but sound is quite good!

Components need to be adjusted for other tubes than EL86