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

[Gary Schafer]

I saw your updated schematic and yes you have the grid shunt in the right
place. But now you want to lift the ground on the 56k resistor and place it
between the other two contacts of the relay so that it is in series with the
zener to the center tap and the relay shorts out the resistor on transmit.
That way you never have the cathodes open during switching.

Don't forget to place the safety diode from the junction of the plate meter
shunt and HV choke with the cathode to the choke and the other side of the
diode to ground. This keeps the negative side of the HV close to ground in
case a tube or something should short.
You will have to calculate the voltage drop across that shunt first.
Well, I just did and it looks like you will have 7 volts drop across it and
you would need 14 diodes in series there! The diode has to have a higher
voltage drop than the shunt or it will screw up the meter reading.
You may want to use a much smaller shunt resistor there and then drop the
series resistor down to the proper level. You may still need a couple of
diodes in series there if you can not get the shunt to a low enough value
for the meter movement you have.

Then you should put back to back diodes across the shunt, again you may need
more in series depending on the shunt value you end up with.

Also back to back diodes across the grid shunt should be done to so you have
protection for the meter in that circuit. You may have to do the same
calculations to see how many diodes are needed.
Be sure to bypass all of those diodes with a .01 or so or they can rectify
any stray RF and mess up your metering.


The chokes in the 922 from grid to ground with bypass caps was to raise the
grids slightly above RF ground to give some added negative feedback. Heath
and Collins also did the same. Some amps have a problem with stability when
that is done.

As far as the neutralizing circuit in the warrior, I would leave it alone.
That is a good circuit and should help stability.

Looks like you are on the right track!

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Rick Poole WA1RKT
> Sent: Saturday, November 22, 2014 10:39 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: Saturday, November 22, 2014 11:13:46 PM
> >>
> >> Put your original 2.2 ohm grid current shunt from fil center tap
> >> to ground and the 390 ohm meter multiplier to the meter switch.
> 
> But, the TR relay and the bias zener go between the fil center tap and
> the junction of the 2.2 and 390 ohm resistors, right?  That's how the
> TL-922A does it, and how I do it in my latest schematic under the UPDATE
> (11/22/14 2115 EST) label on the web page.
> 
> You mentioned the Kenwood Tl-922, so if I may digress a bit... Any idea
> why Kenwood grounds the tube grids thru chokes and capacitors rather
> than directly using big fat low-inductance connections?  That's more or
> less the way Ameritron did it with the AL-811H and it was nothing but
> trouble for two years before I got rid of all that stuff and directly
> grounded the grids, and the thing has been happy and stable ever since.
> 
> Rick WA1RKT
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