[AMPS] Equalising voltages on series connected electrolytics.

[Dave Kirkby]

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 ?

G8WRB


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm