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Old 11th Jul 2020, 9:40 am   #21
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 3,129
Default Re: Hope to start an audio amp with CV415/CV4046/TT15

One option for the bias supply would be to generate a negative as well as a positive output from the existing HT winding. It would just need a couple more diodes, connected the other way round. This gives you way too many volts of course, but compared with the 5V winding, which gave you way too few, it's not much more 'wrong'. You'd then just drop down to the voltage you want with a resistive divider. 300V at 5-10mA across the divider would only see you having to dissipate 1.5-3W. You wouldn't be working the mains transformer much harder if it's got a centre-tapped HT winding anyway. You'd ideally want a reservoir cap immediately after the diodes, to deal with the worst of the ripple, but it could be low value given the small current draw. You'd do most of the smoothing across the lower leg of the divider, where the voltage would be much lower.

Cheers,

GJ
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