Ron,
Check for open bleeder resistors. 73, Tony W4ZT
w2cqm@juno.com wrote:
> 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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