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Intermittent RF Output on Early Low Power Novice Transmitters




 
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Author Topic: Intermittent RF Output on Early Low Power Novice Transmitters  (Read 72 times)
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DMOD
AC0OB - A Place where Thermionic Emitters Rule!
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« on: February 12, 2020, 02:06:59 PM »

If there is intermittent or low power output say for example, on the Hallicrafters HT-40 or the Knight T-60 or any other transmitter with a Turret-type Bandswitch arrangement, check the coils on the bandswitch turrets for continuity.

Most of these transmitters have those coils arranged in a series configuration and simply short out the coils as you go higher in frequency.

The coils have been known to break at the shorting bandswitch lug and may make partial contact or break the contact if the cabinet is moved or shaken.

Sometimes these coils are hidden behind the series connected wiring and the breaks are not always visible.

Indications: Intermittent output, oscillation at a  lower frequency than the crystal frequency, high plate current indications, and no grid leak resistance between ground and the top of the turret.

Solution: Use a #28 gauge buss wire and solder the end of the coil to the bandswitch lug with 2% silver solder and without any tension.


Phil - AC0OB



 

* Typical Bandswitch Turrent Arrangement.pdf (436.1 KB - downloaded 8 times.)
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