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


Jim Sorenson kjsorenson at gmail.com
Thu Jun 22 10:52:25 EDT 2017


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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