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Old 22nd April 2011, 03:50 PM   #1
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Default PP OPT in SE mode operation?

Hi there,

Please redirect me to the thread if this is already discussed. My search did not show one up.

So I just wanted to experiment this:
Mesa Boogie Patent for Switchable Single Ended, Push-Pull Guitar Amp

I have a couple of SE tube amps sitting and collecting dust, due to too much competetion between them to be chosen by me. I can use either phase splitter tranny or balanced output of a DAC to create two inverted signals, and use two SE tube output stage with one PP OPT.


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Old 22nd April 2011, 04:31 PM   #2
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Patented in 2007!!! This is a very old technique. Some designer needs to be fired apparently. Perhaps the patent is limited to the dual switches only.

In any case it is easy to do a much better job. Just making one pentode into a CCS by grounding the grid is a relatively poor way to do the SE job, all it does is balance the DC current for the OT, but there is no power output from that tube.

What should be done is convert one pentode side to effective triode operation by local "Schade" plate feedback. (this will now require additional grid current drive to deal with the lower input Z of the Schaded pentode) The other pentode side can be left as is (although it is useful to increase the cathode degeneration resistance on the pentode there to make it into a better modulated current source, which would then require additional voltage drive). This way the trioded side controls the voltage output, while the pentode side remains high impedance, but still supplying complementary power (basically slaved). Then the bias of both tubes needs adjusting so that class A operation at least covers the first five or ten Watts or so. (some current/Wattage headroom required in the tubes and power supply to do this)

Finally there is the even better scheme called "anti-triode" which uses the above scheme (with a real power triode normally on the "triode" side) with a CCS tail added to the output stage, and the pentode side gets changed to a high gm device, either by using a Mosfet in its place or a gm booster circuit added to the pentode side. It is capable of equivalent sonics to true SE designs, with increased power and better speaker damping besides. Search on "anti-triode" to find a half dozen threads on the subject.

Last edited by smoking-amp; 22nd April 2011 at 04:49 PM.
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Old 22nd April 2011, 04:59 PM   #3
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I think the patent is for "difference in sounds at your finger tip" rather than better sound or improvement.

Thank you for the suggestion and I found this thread which I can do some experiment from.
My version of the Simple EL84 or rise of the anti-triode.
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