Choke input filter type power supplies require a quite a bit of bleeder
current to prevent voltage soaring like you describe. You can find more
information about this in your handbook. I suggest you confirm that the bleeder
resistor(s) are in good condition.
73/k5gw
In a message dated 11/18/2005 8:23:58 A.M. Central Standard Time,
w2cqm@juno.com writes:
Since I'm relatively unfamiliar with the characteristics of a vintage
Henry 3KA choke input power supply, perhaps someone would comment on a
question that has arisen regarding what appears to be too high an output
plate voltage. The Henry is equipped with a 10Hy fixed choke tuned with
a .1mFd @ 7500VDC capacitor. The diode configuration is full wave bridge
with the choke wired in series and situated before the filter capacitor;
for a typical choke input circuit. All components are OEM Henry. A Plate
transformer output is 3300VAC with a nominal input rating of 230VAC.
There's a 4 terminal manual step start power up switch (position 1-off),
voltage fed through resistance wire in position 2 for the soft start,
a CW tap (position 3 which shorts out the resistance), and a third SSB
tap, position 4. In the no load CW position, DC voltage is over 4KV and
in the SSB (higher tap) position the plate voltage is close to 5KV.
Henry only provides a full scale plate meter calibrated for 4KV so the
dial deflection obviously is off scale. These high voltage values are
verified independently with a calibrated Triplett meter. In addition,
they appear to be significantly higher than the levels suggested in the
operator's manual. Tested the choke for resistance (about 56 ohms) and
the tuning capacitor is not shorted. My primary voltage is somewhat
higher (248VAC) so that may account for some of the overvoltage. However,
to my mind, the resulting operating voltage is at least 800-900VDC too
high and of course is causing some concern. I've verified that the wiring
is correct and I'm asking for any comments that may explain the higher
levels of plate voltage. Any comments would be appreciated. Ron W2CQM/3
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