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RE: schematic

Reason for use the OPT ``split bobbin `` coil configuration for Circlotron output power stage is to get the perfect primary load symmetry & balance for both Circlotron PP output power stage phase , since the Circlotron topology use the whole OPT primary coil , not only the half of the OPT primary coil which is normal for classic based OPT tube PP Amp .
That`s mean equal OPT parasite capacitance & stray inductance for both half of the output Circlotron PP power stage & more important is to get minimum and Equal parasite capacitance between primary and secondary Circlotron OPT coils .
Usually there is no any DC flowing thru the Circlotron OPT primary coil ,so there is no appearance of switching transients ! , (accidentaly same as for SE parafeed configuration ), and central primary coil earth tap it is necessary only to get the ground reference point for driver stage unit & power stage bias , since the Atmasphere OTL Amps use two equal 600R resistors from each ``floathing `` speaker terminals conected to Amp star ground point for that , that is the reason why yours OPT CT don`t have to be grouded at all.
The best iron core for Circlotron output power stage it is not critical as for standard SE or PP based Amps ,and it is physically much smaller than ordinary PP OPT for the same projected output power , but in the same time it is with much wider both high & low Audio frequency ends response .
For low step up/down ratio request quality toroids finish the job 100 % , but for higher step up/down Circlotron OPT ratio the double C core iron with middle inserted split bobbin coil is far the best solution !
- Hi impedance VC is not heavier than low impedance VC ,since the high impedance coil is made of very tiny isolated Cu. wire ,this type of speaker it is ``excited`` with average relative high voltage signals from OTL Amp but with relative low average signals peak current for the same distributed power .
Friend of mine have reconed 12``/ 15W speaker with 2500 ohm VC !!!,``excited direct via condenser from 6l6 SET anode (parafeed), Sonic difference is huge compared with normal OPT based 6l6 SET ,and thats excellent system sound it is the normal appearance for pure tube OTL Audio !!! .
Best Regards


Edits: 08/20/11
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