[SignalOne] Tuning the Broadband

[jerry]

On 2024-11-18 17:06, parinc1 wrote:
> Hi Jerry,
>  I always like reading your posts. Doing a great job and you have
> found some difficult problems already.
*** Thanks.

>  Take a look at what  my 1296MHz EME buddy went through to straighten
> out  a CX-7 he inherited. What a butcher job had been done to it:
>  https://www.sm2cew.com/CX7A/CX7A.html
> 

*** An interesting page.  He did a lot of work on that.  I notice
that he used a TDA2030 audio module.  Slick the way he mounted it to
the power supply board.  I have a baggie of those exact same modules.
Tempting.  Those modules are advertised as "18W", but working off
12V, they'll only do a bit less than a watt.  And the electrolytics
on board are only 16V.  I don't think one would want to do much more
than that with that tiny heatsink anyway.

   I was thinking of using a digital amp - those will make lots of power
with no heatsink at all.  But they make RF.

                 - Jerry, KF6VB




>  Dale W4OP
> 
> -------------------------
> 
> FROM: signalone-bounces at mailman.qth.net
> <signalone-bounces at mailman.qth.net> on behalf of jerry <jerry at tr2.com>
> SENT: Monday, November 18, 2024 4:30 PM
> TO: Signalone <signalone at mailman.qth.net>; Signal One
> <signal-one at groups.io>
> SUBJECT: [SignalOne] Tuning the Broadband
> 
> This list is for discussions regarding collecting, repair, use and
> sale of Signal/One radios and accessories.
> 
> Documentation on Signal/One radios can be found at
> http://www.hamanuals.com [1] and several other sites on the Web.
> 
> .
> The challenges continue...
> 
>    Now that I have decent power on the lower bands ( still pretty much
> zilch on 10M ) I'd like to
> tune up the broadbands.  The schematic makes it obvious that they're
> just preset tunings for the
> PI-L network - a separate trimmer for each band.  So you reasonably
> tune
> them just like the big
> TUNE and LOAD knobs.
> 
>    They're hard to get at.  Especially the plate TUNE trimmers.  And
> they're stiff.  I was trying
> to tune 20M into submission - you can't get straight the tune with a
> screwdriver.  It's complicated
> by trying to do it *fast* before the tube cooks.
> 
>     The hexes around the screws are 7/32.
> 
>    What do YOU use to tune these things?  I have an open end ignition
> wrench that will work.  I really
> don't like poking around with conductive metal tools that can slip off
> while this thing is running.
> 
>    I'm thinking to take a 7/32 socket.  Turn it down on the lathe so
> it
> fits inside the trimmer mounting
> screws.  Cut it down really short so it fits in the 20M trimmer.  Weld
> a
> handle to it.
> 
>    Replacing the screen current sensing resistor really helped the
> transmit.  It's still not quite right
> though.  I have to turn the drive all the way up to get decent power.
> And still zilch on 10M.  Too me,
> that says there's a bad stage somewhere.  On lower bands, the system
> has
> enough excess gain to compensate.
> 
>    Checked into a roundtable on 20M this morning.  Got good reports.
> Rig
> was making full power.
> 
>                    - Jerry, KF6VB
> 
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