[Elecraft] Slightly off top amp question

[peter gerba]

Hi David and Vic;

David in addition to Vic's suggestion you might want to check the input
circuit on each band with a grid dip meter to confirm the settings. If bad,
look at the slugs in the input coils (if used) for cracks or breaks or check
the compression Caps (if used) for proper operation.

Is the grid current the same on all bands, proper output or not?

Vic is on the money with input switch problems.. check the contacts. Clean
them and check them again.

gl, pete

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net]On Behalf Of Vic K2VCO
Sent: Tuesday, June 27, 2006 7:52 AM
To: David Douglass
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Slightly off top amp question


David Douglass wrote:
> Apologies in advance for the off topic question!
>
> I've just bought an old FL-2100B amp to do up, and run with my K2 (I have
> the bits and pieces on order for the external keying circuit!!).
>
> When trying the amp out I found that I am getting a pretty high input SWR,
> and thought I should Align the input coils on the amp.
>
> This seemed to work OK on 40m, and 15 and 10m are not too bad (~2:1), but
I
> have a very high input SWR on 80 and 20 irrespective of where I tune the
> slugs.
>
> It looks like the valves in the Amp are the original Centron 572B/T160's,
> which are lighting up, but are obviously very old (>20 years I would
> imagine).
>
> If the valves were on the way out, could this account for my inability to
> tune the input coils, or should I look elsewhere for the problem ?

Are you getting reasonable output on the bands where the SWR is OK?  If
so, then the problem is not the tubes (valves).  Check that the
bandswitch is indexing properly.  Also, a problem in the output tank
circuit can cause a high input SWR -- look very carefully at the
bandswitch contacts to verify that they are not burned and are indexing
correctly.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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