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Old Yesterday, 02:53 PM   #1
316a is offline 316a  England
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Default DC coupled SE SChade amp

I have read quite a bit about Schade feedback on here but have hardly scratched the surface with pentodes . Was thinking about building a simple DC coupled SE amp but with an EF95 input stage as I belive these can work at low voltages . Output stage will be a 6P15P , EL822 or similar ~12 watt pentode . I'm yet to work out component values , I have built a similar (all triode) amp which worked very well but need some opinions as wether this one is a go-er

cheers

316a
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Old Yesterday, 05:47 PM   #2
mogliaa is offline mogliaa  United Kingdom
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Hi 316a,
Seems a good starting point to me. I've been playing with a 4P1L with Schade feedback but using a FET/BJT driver instead as per Michael Koster's version.

As the FB will be determined by the un-bypassed cathode resistor and the pentode anode resistance in combination with the Rf, you will have to estimate ra and use a pot as Rf to set the right level of FB. You can do this and monitor the harmonic profile to avoid ending up with a pentode sound rather than a more triode-like one which I guess you would prefer.
cheers
Ale
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Old Yesterday, 06:19 PM   #3
316a is offline 316a  England
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Thanks ! The cathode resistor of the driver pentode will be passing the current of the output stage through it . It tends to help self-stabilise the amp (if it works like it does in my 6S45/2A3 amp) and will be much lower in value than usual , hence should not require bypassing . A bit like filament bias I have placed the driver G2 supply in the cathode of the output valve as well as the driver's cathode resistor . I'm not entirely sure how well it will work and hoping that it will all fit into place without dropping too many volts in the cathode circuit

316a
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