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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