[AMPS] Equalising voltages on series connected electrolytics.

[Rich Measures]

>
>I'm in the process of putting together an amp (with integral psu) that
>uses a conduction cooled tube. My hope is to avoid any cooling fan, but
>it is a tall order, with an anode dissipation of nearly 200~250 W, and
>numerous other sources of heat (screen, grid, heater, psu losses etc
>etc). Hence I want to avoid any avoidable heat generation.
>
>I was wondering if instead of putting lots of power eating resistors
>across each of the caps in the HT supply (8 x 400 uF, 350 V), it would
>be possible to use a non-linear device, such as a voltage dependant
>resistor (VDR) or zener diode (ZD). In principle, one would only need to
>pass the capacitor leakage current, rather than several times this,
>which is needed with standard resistors. Hence the power idssiaption
>could be reduced dramatically.
>
>I realise the other function of the resistors (safety discharge) would
>not be performed by such devices, but resistors for this can be much
>higher in value and therefore dissipate far less power.
>
>I see two problems:
>
>1) Zeners (or to be more precise avalance) diodes are not available at
>high voltages, making it necessary to use two or more in series across
>each cap.
>
>2) I dont know how VDRs would mind being on the point of conduction for
>long periods.
>
>Any thoughts ?
>
More complicated is not always mo betta.  .  I would use Matsushita 100k 
ohm 3w resistors to equalize DC filter capacitor potentials.  These 
resistors dissipate minimal P, are stable, accurate, and discharge the 
capacitors fully.  We have sold over 5700 of them, and have not heard of 
one failure.



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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