[AMRadio] Barker-and-Williamson-850A-tank-coil-assembly need to make new spacers


Alan Victor amvictor at ncsu.edu
Thu Jun 22 10:59:47 EDT 2017


Jim,

I have both choke styles and measured both with a GDO for anti resonance
via the shorted terminals. Indeed the 175 is problematic near the 15 meter
band and the 175 A solves this issue. You can modify the 175 per rewinding
the last top section and there are notes on this subject. Alan W4AMV

On Thu, Jun 22, 2017 at 10:52 AM, Jim Sorenson <kjsorenson at gmail.com> wrote:

> Gentlemen,
>
> ​I'm putting back into service a vintage amp that uses the
> Barker-and-Williamson-850A-tank-coil-assembly​. The plastic (?) coil
> spacers are long gone and I need to make new ones. I once saw a practical
> way to do this with smaller coils a while back, but lost the reference.
>
> Any ideas would be appreciated before I try and make a mess of it.
>
> On another note, the amp uses a National R175 RF choke, not the R175A. The
> R175 was designed before 15 meters came into being so the question of stray
> resonances for that band might be a concern. My 1942 Radio Amateur's
> Handbook show the National ad for this choke, which reads "The reactance is
> high throughout the 10 and 20 meter bands as well as 40, 80 and 160 meter
> bands. Inductance of 225 uh., distributed capacity 0.6 mmf., DC resistance
> 6 ohms, DC current 800 ma., voltage breakdown to base 12,500 volts."
>
> Is it time for a modern replacement?
>
> Many thanks,
>
> Jim
> W3BH
> Saxonburg, PA
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