Electronics > Beginners
how do I get the negative grid bias voltage without a tap on my power transformr
(1/1)
ELS122:
is there any way I can get the ~-40v for fixed bias on 6BG6G's without a tap on the power transformer?
Ian.M:
Balanced charge pump (i.e. capacitively coupled bridge rectifier) driven by the secondary feeding your HT rectifier, shunt regulated to your desired bias voltage. Choose the charge pump coupling capacitors to limit the current to only slightly over the max load on the bias supply, at min. AC line voltage, so that most of the voltage drop required is reactive in the coupling capacitors, to keep the dissipation in the shunt regulator's feed resistor fairly low.
N.B. the bias supply will come up relatively slowly compared to the HT supply, which can be an issue if the cathodes are already hot when AC to the transformer supplying the HT rectifier is switched on.
Jr460:
A quick google shows some ideas of how to do it with getting complicated.
http://www.valvewizard.co.uk/bias.html
ELS122:
--- Quote from: Jr460 on January 28, 2020, 07:52:23 pm ---A quick google shows some ideas of how to do it with getting complicated.
http://www.valvewizard.co.uk/bias.html
--- End quote ---
well that's exactly my goal, getting it too complicated for no reason :-DD
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