[Boatanchors] Please review & comment on my Heath Warrior HA-10 amplifier design changes

[Gary Schafer]

Another of the joy's of a choke input filter.
With the choke input filter you can't just arbitrarily change the bleeder
resistor size. You need a minimum load on the supply or the voltage will
soar very high with no load.
Right now the output voltage should be around .9 times RMS voltage of the
transformer. Without a substantial load it will start to look like a
capacitor input filter and the voltage can go as high as 1.4 times
transformer RMS voltage with no load.
You have a 1700 volt RMS transformer each side of center tap. .9 times that
with a choke input filter and proper minimum load gives around 1530 volts.
With out the proper minimum load the voltage can climb up to 2300 or 2400
volts. 
You need to calculate the minimum load needed.

Again, leave the grid metering resistors alone. Otherwise you are going to
have to jockey 3 sets of resistors around to get all the readings right. You
already have the proper values for the grid.

You need to reduce the plate current shunt resistors to a much smaller value
so you can put a diodes around it and select the proper series meter
resistor for it to read right.

Don't forget the diode to ground from the B- of the power supply.

Yes there can be positive or negative current depending on what should arc
or short. That is the reason for back to back diodes.



> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Rick Poole WA1RKT
> Sent: Sunday, November 23, 2014 7:35 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Please review & comment on my Heath Warrior
> HA-10 amplifier design changes
> 
> 
> From: "Gary Schafer" <garyschafer at largeriver.net>
> Sent: Sunday, November 23, 2014 5:03:35 PM
> >>
> >> Moving the meter series resistor to the other side will give
> >> you the same circuit that you now have but it will screw up
> >> your meter when switched to plate current and plate voltage.
> 
> Good evening, Gary.
> 
> For the plate current, I'd have to reduce R11 from 10K to 9.61K... a
> relatively insignificant change, but in any case one that can easily be
> done.
> 
> As for the plate voltage circuit, I'm changing the bleeder and shunt
> resistors anyway.  It's nuts to have a 60K 100 watt (!!!) bleeder
> resistor there, generating all kinds of heat.  I have calculated several
> combinations of bleeder resistor and plate voltage meter shunt that are
> a LOT more reasonable in power dissipation, more like 5 to 10 watts,
> while still giving a reasonable capacitor discharge time.
> 
> >> It wouldn't hurt to also place diodes directly across the meter
> >> for added protection of the meter. even though a lot of voltage
> >> will appear across the meter it may help the meter survive.
> 
> A lot of voltage is right.  The meter would be asked to handle more than
> 10 times, something like 14 times, its rated current.  I can't imagine
> any meter surviving that.  A 390-ohm resistor in series with the meter,
> then back to back diodes (or maybe one diode... can the meter ever see a
> negative voltage?) across the resistor/meter series combination, and the
> most that the meter will be asked to handle is about 1.4 times its rated
> current.
> 
> I'm redrawing the schematic per the changes we all have discussed, and
> should have it up onto the web page in a day or two... gonna be tied up
> for much of tomorrow getting my furnace replaced ($$$$$$$$$-sigh) :-(
> 
> Rick WA1RKT
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