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RE: You don't need expensive power supplies




For sake of clarity this is the basic output totem pole topology used by most non circlotron OTL tube amps (I used a similar one too).

I do not want to bother too much the DIY inmates with these technical details and so this is the basic explanation given by Mr. Broskie (of tube cad journal) of the reason why such a topology is more prone to hum than conventional PP (I would say simply because of its output asimmetry).

I subscribe this simple explanation of Mr. Broskie just because I had found it very applicable to my OTL design and so, in order to reduce the residual 50/100 Hz hum, I knew in advance that I needed a lot PS capacitance (4000-5000 microF or more).

This large capacity requires either the use of some device to limit the current inrush at power on or some retarded relais to exclude some series resistor after full charge of the PS filter capacitors.

IMHO, mandatory use of:
- larger filter capacitors,
- PS power transformers in excess of 500 VA,
- current limiters and/or the like to limit current inrush
will likely result in a more expensive power supply w.r.t conventional PP.

In the case of circlotron OTL I suppose that, as you must use two independent HV power supplies, the inherent better hum rejection of circlotron, which would lead to a more economic PS, is likely offset by the need of doubling the number of HV PS.

This is why I have built only a few OTL amps and many PP amps.

Best Regards
Luca




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