Paul, there is some confusion because there are 2 Commander amps. I
apologize for just glancing over your post and replying in a hurry while
heading to dinner (-;
Yours is the original built by Command Technologies and you are correct, it
does not have load padders. The early versions did not have grid trip either
which is a very poor design....reminds me of the Dentron DTR-2000L.
That switched output toroid (a Micrometals powdered iron 2 mix) is a regular
cause of problems since it is used on 3 bands and develops excessive voltage
and eventually insulation breakdown. Its made worse by that 4:1 toroid that
follows.
Id start by removing most of the cover screws and then powering up and load
as you have been doing while carefully keeping the grid current low. After
maybe 5 minutes power down and I dont think I have to tell you about safety
precautions; youve been around this stuff longer than I and you still have
20 years on me!
When the B+ is all bled feel both toroids for heat, they should be cool.
Also feel the plate blocking cap and plate choke, the cap is more prone to
failure on 160.
If the toroid is the problem the easiest solution is to remove and wind a
new toroid with better insulation on the core and wire as there is no simple
way to undo the engineering problems without spending a lot of money. If the
4:1 looks the slightest bit cooked then make a new one also.
As long as your input VSWR and power is holding steady I dont think that
circuitry has a problem but they are also known for cooking relays.
Carl
KM1H
----- Original Message -----
From: "Paul Elliott" <paab@valornet.com>
To: <amps@contesting.com>
Sent: Wednesday, January 25, 2012 5:00 PM
Subject: Re: [Amps] 3CX800A7 Grid Current Problem
> Thanks for the replies. I, too, at first thought it would involve a
> padder
> in the output tank circuit. Something I should have out in my first post:
> there are no padders in the output circuit. The schematic I have shows an
> output circuit that is a Pi network (the inductance is an air core coil in
> series with a toroid inductor) into a toroid transformer (I am guessing
> it
> transforms about 200 ohms down to 50 ohms).
>
>
>
> The input SWR is 1.2:1 on 160 m.
>
>
>
> The grid current will also take off on the other bands if the loading is
> way
> too low. I have a lot less trouble if I always start with the factory
> settings. On any band I always start the tune up with very low power,
> about
> 10 watts, and tune for max power out. I then unkey the amp, increase
> drive
> power to about 18 watts, and key the amp while watching the grid current
> meter to be sure it doesn't take off. I then quickly swing the tuning and
> loading caps slightly above and below where they are tuned to be sure the
> grid current doesn't take off when they are changed, then retune for max
> output. I repeat this procedure three or four times to get to the power
> level I want. As I said, there is no grid over current trip out on this
> amp.
>
>
>
> I need all the power I can get on 160 m to bust thru the local QRN and
> pile-up on HK0NA.
>
>
>
> 72 Paul W5DM
>
>
>
>
>
>
>
> --
>
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