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Re: [TenTec] Century/21 Final Module Different than Schematic

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Century/21 Final Module Different than Schematic
From: David Goncalves <davegoncalves@gmail.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 16 Mar 2018 10:39:25 -0400
List-post: <mailto:tentec@contesting.com>
A quick drawing of what I see: https://imgur.com/a/y2FqO


On Fri, Mar 16, 2018 at 8:24 AM, David Goncalves <davegoncalves@gmail.com>
wrote:

> Hi folks,
>
>  I am repairing a radio that was previously 'fixed up'; the final was a
> real mess, and no surprise, one of the MRF475s is broken. That is, the leg
> of one of the transistors is broken off. Wow. So much blobby soldering and
> flux, could hardly tell what was going on.
>
>  As I was working on cleaning this mess up, I noticed that the module's
> design is a bit different than the available schematics. On this amp board,
> instead of a single bias adjustment, there are two - one for the AB driver
> (as expected), and the other for the final pair. The circuit for the final
> pair bias is a copy of that used for the driver, and it is applied to the
> bases of the MRF475s through the low-turn-count base windings of the driver
> to final stage transformer.
>
>  At some point I'll have to adjust these pots after the repair. I'm going
> to figure that the 'set for 6mA bias' from the manuals is not valid here.
>
> I have some guesses on how to adjust this circuit - but what do you all
> think? Or, is there somebody with an older revision of the manual that
> describes how this is done?
>
> Thanks,
>
> --
> David Goncalves
> W1EUJ
>



-- 
David Goncalves
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