A public thanks to N6KB Ken who reminded me that a separate bias procedure
was needed for the finals. I had done the bias adjustment in the PA can,
but that wasn't for the finals. Thankfully I had yet to transmit so I
didn't splatter my signal across the spectrum.
Paul
AC8OI
On Tue, Oct 22, 2013 at 1:09 PM, denton sprague <denton@oregontrail.net>wrote:
> reminds me of having to tighten down all the nuts, bolts and screws in the
> final bricks of my old TT Delta and Paragon II rigs….heat from the finals
> and B+ connectors to the finals would cause the hardware to work a bit
> loose.
> I was running a lot of full bore out rtty in those days!
>
> On Oct 22, 2013, at 8:37 AM, Paul Harker <paul.r.harker@gmail.com> wrote:
>
> > Much thanks to all who contributed to the thread regarding my OMNI C.
> I'll
> > save you the long and whining road of my internal torment, but I ended up
> > going with a matched pair of Motorola MRF458s (same as original). I took
> > the middle road between "it's not worth fixing" and "better than original
> > parts".
> >
> > Including a shipping and a pair of 3.3 ohm resistors to replace two which
> > had developed a tan, the repair was just under $70 -- not including a
> much
> > needed upgrade to my soldering station.
> >
> > Final assembly and checkout revealed another problem, possibly what
> caused
> > the meltdown in the first place. The 13.x volts to the PA goes to a
> > pass-thru connector consisting of a nut, screw, insulators, and two
> > star-washer type solder lugs, one on the inside an one on the outside.
> >
> > The solder lug on the inside had developed a high resistance (hundreds of
> > ohms) between itself and the pass-thru nut/bolt. This resulted in a low
> > voltage to the finals, but proper voltage to the driver stage which has a
> > separate power pass-thru. It wouldn't be hard to see how that could blow
> > the finals.
> >
> > I replaced the MRF458s without incident, cleaned up the 13.x VDC power
> feed
> > through, and had previously found and replace a leaky sense diode in the
> > SWR meter circuit. All seems back to normal, except for my frayed nerves
> > whenever I turn up the DRIVE control.
> >
> > Thanks again to all who contributed answers to my original thread!
> >
> > Paul
> > AC8OI
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> >
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