[Hallicrafters] Possibility for improving SX-71 stability

[Philip Atchley]

Hi Y'all,

After going through and overhauling that SX-101A for a friend I took note of 
some of the things that the designers did to aid frequency stability and I'm 
thinking of incorporating some of them into my SX-71.  This set, while great 
for AM SWLing, has never been overly stable on SSB/CW.

Here are some changes I have in mind. Suggestions, Pro and Con are welcome.

1.  A filament transformer to keep the HF Oscillator, 1st mixer, 2nd 
Converter and BFO filaments always lit (should keep things a little warm).

2.  Try to find one of those 3.3 KOhm "heaters" from a parted out 101 and 
mount it adjacent to the under chassis coil compartment.

3.  Mount a small, 3 inch 12 Volt DC fan on the underside of the lid (NO 
holes drilled), OVER the power transformer and run it on rectified, filtered 
6.3 VAC filament supply (about 8.5VDC) for reduced noise.  I now set a fan 
on top of the receiver and it helps a lot.

4.  Replace the Rectifier tube with silicon rectifiers and equalizing 
resistor in an old tube base, AND replace the VR tube with a Zener diode of 
suitable Voltage and power rating, this to prevent VR tube overcurrent 
during "cold tube" start-up.

73 de Phil,  KO6BB
http://users.mercednet.com/beaconeer/
Merced, Central California, 37.3N  120.48W  CM97sh

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* RECEIVERS:                                      *
*  #1. Homebrewed "Mitch Lee" Design              *
*  #2. Hallicrafters SX-71 (1955)& VLF Converter  *
* ANTENNAS:                                       *
*  #1. 20 Meter long "loaded" Sloper oriented E/W *
*  #2. Half Sized G5RV Inverted Vee oriented N/S  *
*  #3. Roof mounted Hustler 6BTV 6 band Vertical  *
*  #4. 15 Meter-band Inverted Vee oriented NE/SW  *
*                                                 *
* Number of different NDB's heard: 974            *
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