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

[Gary Schafer]

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. 
Leave it where it is and place the diodes across the grid shunt resistor as
explained earlier.

Your best bet on the plate current metering is to change the plate current
shunt to a lower value and change the 10k series resistor to proper value,
then a diode or two will work on that.

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.

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Rick Poole WA1RKT
> Sent: Sunday, November 23, 2014 8:17 AM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Please review & comment on my Heath Warrior
> HA-10 amplifier design changes
> 
> Hmmm... Actually, no, the back to back diodes across the meter won't do
> squat.  The meter only sees 0.05 volt at full scale.
> 
> Now I'm considering moving the grid current's 390-ohm series resistor to
> the meter side of the switch, and placing the back to back diodes across
> the series of the meter and the resistor.  At full scale the meter and
> resistor in series will see 0.44 volts.  Back to back 1N4148-type diodes
> should clamp that to around +/-0.6 volts, which the meter movement
> should be able to easily tolerate without damage.
> 
> (Not really sure I need "back to back" diodes... is there a failure mode
> wherein the meter could see a significant negative voltage?)
> 
> I'll have to adjust the series resistances for the other meter
> functions.
> 
> Rick WA1RKT
> 
> ----- Original Message -----
> From: "Rick Poole WA1RKT" <wa1rkt at comcast.net>
> To: boatanchors at mailman.qth.net
> Sent: Sunday, November 23, 2014 7:12:28 AM
> 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 12:16:43 AM
> >>
> >> 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.
> 
> Wouldn't back to back diodes, maybe Schottky diodes, across the meter
> itself take care of that?
> 
> Rick WA1RKT
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