[Hallicrafters] Crystal Issue

[Wj5mh at aol.com]

I've been working on an old Hallicrafters HT-40, and I'm finally getting 
around to putting it on-the-air, but I noticed a problem in the oscillator 
circuit.

While waiting for four crystals to arrive from JAN, I used the original 
FT-243 3.5 MHz calibration crystal from an SX-140 receiver to test the 
transmitter.  When power was applied to the oscillator circuit, the crystal 
started immediately and was stable.  On the other hand, stability of the JAN 
crystals at power-up ran from "OK" to "forget it."

The worst crystal was cut for 7.059.  On startup, the crystal would increase 
in FREQ, fall, jump up in FREQ, and then stabilize.  Hence, the initial 
several seconds of each transmission were next to useless.  The crystal for 
7.0199 seemed OK.

To resolve the issue, I added two 100 ohm resistors in series with one on 
each side of the xtal socket.  All crystals are now stable when the 
oscillator is initialized.  Were the new crystals being overdriven because 
they weren't made the same as the FT-243's?  What have I done?  All 
resistance's and voltage readings taken in the circuit were per schematic.

Thanks!
Joe ( WJ5MH )





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