Thought this was interesting no OT

[nosaj]

https://acidbourbon.wordpress.com/20...tar-amplifier/

nosaj

[mozz]

Does OTL have any sort of damping factor?

[nosaj]

Does OTL have any sort of damping factor?

That's above my paygrade, I'd never heard of OTL so was just putting it out there.

nosaj

[g1]

Only do-able with high impedance speakers. The ones I'm aware of were 600ohm Philips. Rare and expensive.

[mozz]

There are some tubes(with enough of them) you can use with regular speakers(8ohm 16 ohm), 6as7?

[g1]

Yes, if you use enough of them you can probably do it with any tube. But you may end up with an amp that looks like EINIAC.

[nosaj]

Yes, if you use enough of them you can probably do it with any tube. But you may end up with an amp that looks like EINIAC.

Just imagine the PT.

nosaj

[eschertron]

Just imagine the PT.

nosaj

Run the heaters off the line. 19 x 6.3 = about 120vac.


just kidding.

[mikepukmel]

Yes, if you use enough of them you can probably do it with any tube. But you may end up with an amp that looks like EINIAC.

Ooo, that sounds like a build challenge!

[R.G.]

The circuit shown is a self-split push-pull circuit. It was invented to get an active cathode follower "push pull" output to get lower output impedance from a tube stage as well as high gain. It was a variant of the "mu-amp".

Historical notes:

OTL was the Holy Grail of amp makers back in the days when tube amplifier design was all there was. The high fidelity industry recognized that the OT was a big limiting factor in getting to lower distortion. The OT itself contributed distortion and limited bandwidth. At the same time, it contributed so much phase shift that amps could not remain stable while having enough gain and feedback to feedback-out the distortions.

So the high fidelity world flirted a lot with how to get rid of the OT. the big limiter was, as noted, the low currents possible with practical setups of tubes. This was attacked with high impedance speakers and barely-possible arrays of tubes. High impedance speakers traded higher output voltages for lower current, which helped the low-current tubes swing them, but high impedance speakers have lots of turns of fine wire, high internal capacitance, leakage fields and nonlinearities of their own.

The electrostatic speaker movement was one attempt to use high voltage, low current tube outputs directly, to eliminate the OT. Unfortunately, electrostatic speakers need voltages in the thousand volt range and so they tend to need step UP transformers to drive them well. Sigh.

[Helmholtz]

The circuit is also known as SRPP (Shunt Regulated Push Pull):

https://www.tubecad.com/may2000/index.html

http://www.valvewizard.co.uk/SRPP_Blencowe.pdf