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Simple tube circuit transforming push-pull output transformer into single ended one
Simple tube circuit transforming push-pull output transformer into single ended one
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Old 7th August 2019, 06:49 AM   #11
KeesB is offline KeesB  Netherlands
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I see that many of you make the same mistake. The Pl519 is floating. It's not earthed.It's indeed a circlotron . The drawing by PPR is wrong because he is earthing the 519 part. The 519 takes 0.1A at 90volts so dissipates 9watts. It's not absorbing half the audio power which can be verified by switching the 519 on and off and you'll find that it has no effect on the power output (other then when it's off there's no bass anymore and there's increased distortion)
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Old 7th August 2019, 06:59 AM   #12
Chris Hornbeck is offline Chris Hornbeck  United States
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Well, it has to operate across the primary of the output transformer. Real volts of signal appear there.

All good fortune,
Chris
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Old 7th August 2019, 07:08 AM   #13
KeesB is offline KeesB  Netherlands
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Lampie: It works very well in a dynamic environment as the VT4C's work in class A.The anode currents of the two VT4C's remain rock steady so does the anode current of the 519.

Besides, I would not publish the schematic of an amplifier if it didn't work well. So it's not merely an idea, I built it and it works very well too; I simply wanted to share this with the audio community because in this forum and others I have more than once met the question if a pp ot could be used as SE and this is the answer.
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Old 7th August 2019, 08:04 AM   #14
Chris Hornbeck is offline Chris Hornbeck  United States
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To really be successful, the constant current generator needs to work over the whole range of signal voltages present. An ideal c-c generator with a 90 Volt capability stops working at 63.64 Vrms, or .61 Watts across 6600 Ohms. Above the signal swing capability of the c-c source bad stuff will happen.

All good fortune,
Chris
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Old 7th August 2019, 08:20 AM   #15
Lampie519 is offline Lampie519  Netherlands
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If it works then it is very interesting indeed.

In this case a standard transformer can be used (without gap).
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Old 7th August 2019, 08:35 AM   #16
KeesB is offline KeesB  Netherlands
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To PRR: in redrawing my schematic you made a very serious mistake by earthing the floating counter current circuit around the 519. O course, that way the whole circuit wouldn't work. I can imagine the mistake because the only type of amp that uses the floating principle is the circlotron otl the difference being that in the otl the ac load is in the cathodes of the powertubes while here it's in the anodes. The other difference is that in the otl is a balanced circuit in which both halves of the powerstage are driven while in mine only the VT4C's are.

The VT4C's with their 1000v powersupply and the 519 with it's 90v powersupply are completely independant ; the VT4 part is earthed while 519 part is not This is the essence of this circuit. Both parts only share the output transformer and because the currents are the same but flowing in opposite directions the voltage across the OT is zero (or very close to it) and only ac voltages, the audio signal remains. Exactly this happens in a circlotron only the currents that flow through the speaker (in both directions) run into amperes but they cancel one another so no damage to the speaker occurs.
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Old 7th August 2019, 08:36 AM   #17
Kay Pirinha is offline Kay Pirinha  Germany
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I'm quite sure the 910 Vdc note across the last multiplier capacitor isn't true and severely misleading. Supposedly it is meant from the output tube's plate to ground.
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Old 7th August 2019, 09:05 AM   #18
Lampie519 is offline Lampie519  Netherlands
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I guess the heater for the PL519 is floating. In this case i would create a DC voltage to drive the G3 of this tube making it a better follower.
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Old 7th August 2019, 10:18 AM   #19
DF96 is offline DF96  England
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OK, I think I get it now. It is essentially a biased adjustable CCS used to divert the quiescent current away from the OPT.
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Old 7th August 2019, 10:25 AM   #20
KeesB is offline KeesB  Netherlands
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Two answers: there is just 90volts across the last c of the multiplier (it's floating as I have said several times before); of course the filament voltage of the 519 is floating as the whole circuit around the 519 is.

I don't see why a positive voltage on g3 would work better here. It's a current source whose only function is to supply current from a high(est) possible impedance so as not to load the output tubes and I don't think a positive voltage on g3 would contribute to that.
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