[Amps] Solid state amp advice needed

[Jeffrey Madore]

Vic,
You might want to just replace the bad transistors and maybe order a couple
of spares. See how the others perform when you test per your plan. And, I
think your plan is a good one. Watch the DC current to all the boards
simultaneously as you set the idle and then as you apply a small amount of
drive. If the amps go up much quicker on the suspect board, I would switch
that board to another position to verify that it is the board and not the
combiner / splitter.

If the transistors idle nicely but you find the collector current goes up
very quickly with little drive to the amp, I would suspect either that board
is being over driven or there is a mismatch in the collector circuit. Either
way, I would keep the drive as low as possible as you look at RF voltages.

And while you wait for your new components, you can dig out 4 spare panel
meters and wind / calibrate shunts to get the 4 ammeters you need!  I've got
one right here. Meter bolted to 2 copper straps with a short coil of #12
wire soldered to the straps. It looks like haywire but it works like a
champ. I plan to make a few more and box them. Nice meter movements are
cheap at flea markets and high current ammeters can be handy, as most dvm's
have a limited current range.

I also find that soldering the shunt to the meter leads is much better than
bolting it across the meter. The R of the shunt is so low that the torque of
the bolts has too much effect on current division.

Good luck, Vic, and keep us posted,

Jeff - K1LE - CT - ><>

----- Original Message -----
From: "Vic Rosenthal" <rakefet@rakefet.com>
To: "Jeffrey Madore" <K1LE@arrl.net>; "Amps reflector" <amps@contesting.com>
Sent: Monday, November 25, 2002 10:52 AM
Subject: Re: [Amps] Solid state amp advice needed



>
> What I am planning to do now is to replace all 8 transistors, adjust the
bias,
> and then carefully apply drive a little at a time, watching the current to
each
> board and looking at the RF voltage on the output of each board with a
scope.
> That should show up potential problems before they become actual ones.
>
> 73
> Vic K2VCO