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

[Rick Poole WA1RKT]

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