[MRCA] GE Portamobil

[Robert Nickels]

On 2/25/2019 3:44 PM, Ray Fantini wrote:
>   don’t know if it would go up to 80 or not

I've converted a number of them and every one did, but I can't say I've 
done the same model.  Since I'm interested in 3880 and 3885 kHz, the 
cheap crystals from N4ESS work just fine.  I use my programmable 
oscillator board for the receiver, and have done different receiver 
conversions as well.   Of course you have to retune the output circuit 
and sometimes a grid coil, if there is one, and occasionally the 
receiver front-end must be modified to tune up to the 75 meter ham 
band.  160 is within the unmodified range but you'd probably need a 
buffer amplifier to drive the tube-type PA.   The easiest thing is just 
to just bypass the internal loading coil but I sometimes remove them 
because the Airdux and ceramic trimmer capacitors are handy for other 
purposes.   I usually remove the porcelain standoff and add a connector 
for 50 ohm antennas after doing so.

Marine radio shops no doubt had file cabinets full of manuals and 
schematics at one time,  but most have evidently gone to Davey Jones 
Locker as documentation on boat radios is very hard to find.  However, 
if yours is a Sonar model 75A (or B, I have one of each and can't see 
any difference),  I have the manual and will be happy to scan the needed 
information.  These are hybrid radios with solid-state receiver, 
modulator, and DC-DC converter power supply for the three-tube PA (12AQ5 
oscillator driving a pair of 12DQ6 sweep tubes at 75 watts input).  Nice 
for ham use because of low power consumption, and if the band is dead 
you can always flip the switch and listen to the ball game ;-)

Sonar also made a portable called the "Sonarfone" which was designed for 
carry-on operation.   It used battery tubes and got B+ from a vibrator 
that was powered from a 2 volt lead-acid wet cell.  Some of you may 
remember it from when I used it to check into the WWII Net at Dayton 
some years ago,  and thanks to Photobucket for letting everyone's photos 
out of jail, you can now see it again:

smg.photobucket.com/user/ranickel/library/Sonarfone

73, Bob W9RAN