I lifted the 220k bleeder from ground and it measured about 230k, probably not enough of a change to account for such a high voltage. I soldered the bleeder back to ground and untied the connection between the 10k 25w load resistor between the HV and 250v supply. The 250v supply now reads a reasonable 270v while the HV rises out of control (+900v). Reconnecting that 10k back to the 250v supply, the 250v reads over 500v.
I don't "get" how that 10k load resistor is supposed to work? It would make more sense to me if it was tied to ground, but the only way it's getting to ground is through the puny 220k 1/2w resistor on the 250v supply. Tom On 1/15/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
An open 220k bleeder resistor makes sense. I guess you could check that by disconnecting it and checking the resistance. Makes me wonder what would cause it to fail. Assuming 250 volts it would need to dissipate 0.28 watt. If it's a 1/2 watt carbon composition resistor, it might have increased in value over time. Those resistors are known to do that. -------------- Original message -------------- From: "Ken Winterling" <[EMAIL PROTECTED]> > > "Ken Winterling" made an utterance to the drakelist > gang > ---------------------------------------------------------------------- > Tom, > > There is a 220K bleeder/load resistor, R8, across the medium B+, 250V, > supply to ground. If it is open the medium B+ will be pulled up > toward the HV. Let us know what you find. > > Ken, WA2LBI > > > > On 1/14/07, Tom Taylor wrote: > > > Still working on the AC-3... The drakelist wisdom was the 20k load resistor > > > didn't present enough of a load, compared to the original 10k resistor, and > > > that was the reason the HV kept climbing. I ordered a 10k 10w re sistor and > > > it recently arrived and I installed it in place. Note that this resistor > > > connects the HV+ with the medium voltage B+ (which seems odd). With this new > > > resistor, the HV now reads a reasonable and respectable 720v (no load). > > > That's good. But the medium voltage now reads 570v !!! I can't explain it. > > > What's different about the medium voltage supply is I replaced the two 100 > > > uf caps with 330 uf caps and the 80 uf cap with a 120 uf. That's what I had > > > in my junk box. Why is that supply so over-voltage now? Perhaps I have a > > > wiring error, though I carefully checked for errors. > > > > > > Thanks, > > > Tom n7tm > > > > > > ---------------------------------------------------------------------- > Submissions: [email protected] > Unsubscribe: m [EMAIL PROTECTED] - unsubscribe drakelist in body > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > ----------------------------------------------------------------------
