[Boatanchors] Troubleshooting linear amplifier

[Bry Carling]

best I can deterine using GO there is a resonance only at 22.5 MHz regardless of where I set the 
tuning caps or bandswitch. I tried jumpering across the bandswitch and nothing changes.
I
 used both a GDO and also used an antenna analyzer coupled diretly to th
 eoutput point, with everything else an and out of the PI network 
disconnected.

Rotating capacitors makes no difference.

I have not connected a resistor yet.

Bry AF4K

Date: Mon, 11 Apr 2016 13:44:27 -0700
Subject: Re: [Boatanchors] Troubleshooting linear amplifier
From: ianmwilson73 at gmail.com
To: af4k at hotmail.com
CC: ranchorobbo at gmail.com; duvallddennis at gmail.com; boatanchors at mailman.qth.net; flboatanchors at yahoogroups.com

Bry,
Disconnect the final plates, and connect a resistor of equivalent valueof the plate resistance of the driven finals from the plate side of the pi networkto ground. Looking into the output terminal with an antenna analyzer, you shouldnow see something like 50 ohms when the pi network is tuned up.
Please remember to disconnect all this - otherwise you will discover what MFJcharge to repair an antenna analyzer (1,2).
73, ian K3IMW
1: don't ask me how I know2: their rates are very reasonable and my MFJ-259B is as good as new now :)

On Mon, Apr 11, 2016 at 1:30 PM, Bry Carling <af4k at hotmail.com> wrote:
Thanks. No, that is not it.



The voltage and signals are switching the input network just fine. I have checked all of that thoroughly

earlier.  That is why I have drive on each band. The problem has something to do with non-resonance

in the PI Network. The puzzle continues.



> Date: Mon, 11 Apr 2016 08:51:23 -0500

> Subject: Re: [Boatanchors] Troubleshooting linear amplifier

> From: ranchorobbo at gmail.com

> To: duvallddennis at gmail.com

> CC: af4k at hotmail.com; Boatanchors at mailman.qth.net

>

> The Centurion bandswitch has two wafers.  One switches both pi network

> fixed load caps and pi output coil taps.  The other is actually a

> small pc card mounted on the switch (I don't remember exactly) that is

> made to switch input network relays.  There is a pc card with separate

> input matching networks for each band and relays that open and close,

> a pair for each band so the correct network is in line for the

> selected band.  The little board on the bandswitch has a ribbon cable

> to the input network card.  if the amp isn't working on any band the

> bandswitch is probably okay.  Perhaps the 24 v. supply to the input

> network board that powers the relays is out.   That would mean no

> relays or LEDs or anything else work.  The filament supply transformer

> has a tertiary winding to provide the ac that is rectified to get the

> 24 v. filtered dc.

>

>

> Sounds like you have your exciter connected to the antenna jack and

> the antenna feedline connected to the exciter input jack.

>

> Rob

> K5UJ



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