Plate Supply Testing

[k4kyv]

Following that logic Don a 25K bleeder across a 2500V PS will be dissipating 250W. I dont believe Ive ever heard of such a low value used with a 5-25H swinger.

Both the ARRL and West Coast HB's use the 10% of full load current rule which Ive followed for over 50 years without losing 866's, etc. So then a 2500V @ 400ma KW input amp would use a 62.5K bleeder which would dissipate 100W. A typical bleeder was/is 50K or 75K and a pair of parallel 100K/100W were often used. Knowing now the problem with those high value wirewounds Id use 4 50K or 75K in series parallel.

Carl

But what did the plate voltage  soar to at minimum load?  Even if nothing blows up, with poor regulation the CW waveform will be horrendous and the output from the linear or modulator will be excessively distorted.

In addition, the output capacitor must be sufficient, in order to maintain good dynamic regulation.  Just because the plate voltage meter stays still  doesn't mean that the instantaneous voltage isn't jumping all over the place with a varying load.

If you are running a plate modulated AM rig with common power supply for PA and modulator, this won't be a problem because the PA will maintain sufficient minimum load on the supply.

[KA2DZT]

Fred,
    I didn't realize you were talking about a second meter, that makes sense.

I have been wondering if I could use a simple neon lamp as a HV indicator.  The question is would a current limiting resistor, sized for ~2KV, still light the lamp at say 500V?  I would put one on the front of the chassis and one on the back.

Rich

Rich,

Not sure about using a neon lamp as a HV indicator.  If you are referring to using it as a indicator for the bleeder resistors it wouldn't work.  When you use two bleeders in series, two things can happen, depending on which bleeder opens you can have either no voltage or full voltage at the midpoint connection of bleeders.  I'm not sure how a neon lamp would react to having twice the voltage on it if the ground side bleeder opened.  Using a meter is better as it can read half the HV and would still have enough scale left to read the full HV.

Keep in mind, you really do not need any indicator for the condition of the bleeder resistors.  The whole idea only works if you use two bleeders in series.  If you use only one bleeder resistor or two in parallel you can't use this scheme at all.

Using a neon lamp to monitor your HV in general is not a good idea, you really need a meter to be able to measure the voltage.

Fred

[KM1H]

But what did the plate voltage  soar to at minimum load?  Even if nothing blows up, with poor regulation the CW waveform will be horrendous and the output from the linear or modulator will be excessively distorted.

As long as the 10% rule is met and the filter components follow the published info its a non issue. There will always be some sag.

There is no evidence to show that a high value bleeder has any bad effect on SSB.

In addition, the output capacitor must be sufficient, in order to maintain good dynamic regulation.  Just because the plate voltage meter stays still  doesn't mean that the instantaneous voltage isn't jumping all over the place with a varying load.

Thats been covered to death on here.

If you are running a plate modulated AM rig with common power supply for PA and modulator, this won't be a problem because the PA will maintain sufficient minimum load on the supply.

Which is right out of the same HB chapter as the 10% rule.

[KE6DF]

Rich,

Not sure about using a neon lamp as a HV indicator.  If you are referring to using it as a indicator for the bleeder resistors it wouldn't work.  When you use two bleeders in series, two things can happen, depending on which bleeder opens you can have either no voltage or full voltage at the midpoint connection of bleeders.  I'm not sure how a neon lamp would react to having twice the voltage on it if the ground side bleeder opened.  Using a meter is better as it can read half the HV and would still have enough scale left to read the full HV.

Keep in mind, you really do not need any indicator for the condition of the bleeder resistors.  The whole idea only works if you use two bleeders in series.  If you use only one bleeder resistor or two in parallel you can't use this scheme at all.

Using a neon lamp to monitor your HV in general is not a good idea, you really need a meter to be able to measure the voltage.

Fred

It seems to me a lot of these issues could be addressed by including a volt meter in your power supply.

IF you get into the habit of checking the B+ voltage when you turn on the power supply and you notice the voltage is much higher than usual, then you can figure it's possible the bleeder has blown. It's also possible the choke has shorted turning the filter into cap input.

If the output voltage under load is lower than usual, that would  perhaps indicate one of your recitfiers is out and you are running with 1/2 wave rectification.

Also, when you power down, get into the habit of watching the voltage go down.

If it goes down slower than usual, that is also a sign the bleeder is shot.

And, of course, double check the volt meter before you open the supply up to work on it.

Plus, having lots of meters looks cool.