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Thread: Thought this was interesting no OT

  1. #1
    Master Destroyer nosaj's Avatar
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    Thought this was interesting no OT


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    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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    Supporting Member mozz's Avatar
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    Does OTL have any sort of damping factor?

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by mozz View Post
    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

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    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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    Don't forget the joker g1's Avatar
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    Only do-able with high impedance speakers. The ones I'm aware of were 600ohm Philips. Rare and expensive.

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Supporting Member mozz's Avatar
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    There are some tubes(with enough of them) you can use with regular speakers(8ohm 16 ohm), 6as7?

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    Don't forget the joker g1's Avatar
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    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.

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by g1 View Post
    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

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    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by nosaj View Post
    Just imagine the PT.

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


    just kidding.

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    If it still won't get loud enough, it's probably broken. - Steve Conner
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    Quote Originally Posted by g1 View Post
    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!

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    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.

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    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    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

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