[Central-Electronics] 458 vfo

[Steve Hobensack]

    I thought I'd pass along some information on a couple good improvements 
that I recently made to my 458 vfo. There is a nice power supply that will 
power the vfo instead of stealing power from the transmitter. It is the 
little antique radio power supply kit at Antique Radio Supply.   
http://www.tubesandmore.com/     It is part   K-101A   both the B+ and the 
6v filament voltage is regulated. With this power supply, you will be able 
to remove the big power wasting resistor on the back and the regulator tube. 
You still must power the 12v filaments from the transmitter.
     I also made another mod that will make the vfo stable enough for PSK on 
7070 usb. I had an old  Collins PTO (permeability tuned oscillator)  laying 
around unused. I simply phase-locked the second harmonic of the  Collins 
oscillator to the 458 vfo.  The Collins unit was from either a t-368 or 
t-195 transmitter with output 1.5 to 3 mhz. I found it at a hamfest several 
years ago. Perhaps other PTOs will work. I powered up  the PTO using power 
supply K101A which also powers the 458 vfo at the same time. To couple the 
output of the Pto to the 450 vfo, use the "gimmick" capacitor method.  Just 
hook a small insulated wire to the center of the BNC connector on the PTO, 
then wrap it around the rf output wire of the 1626 tube. Attach the shield 
to the 458vfo chassis. You could install a BNC chassis mount connector to 
make a nice job.  The coupling is on the order of just a few pf, but It was 
enough to achieve phase-lock to the 458 vfo.  An easy way to assure 
phase-lock is to listen to the 458 vfo output with an auxiliary receiver.  
Tune up the transmitter to 7070. The 458 vfo should have a fundamental 
frequency somewhere near 5356 khz. Turn on the collins unit. Turn the shaft 
until its output is near 2678 khz . The second harmonic  will be near 5356. 
As you are listening, the two signals will seem to lock together as one when 
you are turning the PTO shaft. When phase-locked, you will notice an 
apparent backlash in the 458 vfo dial. The output is now being controlled by 
the more stable Collins unit.
    I think the r-390 PTO is still being sold at Fair radio. Its output is 
from 2555 to 3555 khz and it should work.

73....Steve....N8YE