[SignalOne] CX-7 Display

Sun Mar 14 20:06:26 EDT 2010

Congratulations Rodger, I've had my CX-7A for about 14 years now and it's
still fun to use on occasion. Nice build quality and innovative for the
time. The Nixies are pretty easy to find surplus as they are the same as
used in several HP counters which cheap these days, the HP 5327 series has 8
of them. They may even use the same drivers. I've had issues with the power
XFMR (I think all early radio SN's had this issue)which I replaced with a
Peter Dahl unit, the series inrush thermistor which I replaced with a CL-11
12A unit SKU# 16F5006 from Newark-in-One. Transistor PA driver, Modified the
power supply with several 3tab regulators. I also modified the Driver board
by applying negative bias from the switched -15Volt supply through
appropriate resistive decoupling and capacitive bypassing cutting of the
drivers until the transceiver is in the TX mode which reduces the heat
dissipated significantly from the regulator supplying the driver voltage. I
don't understand why they didn't do this in the first place. I've also had
an issue with one of the crystal filters (common issue with many old crystal
filtered radios) which center frequency drifts over time up a few hundred
Hertz causing tinny low frequency response on LSB...I removed one of the
filters and replaced it with a resistive network with good results.
The counter board 68K and 56K resistors were replaced with ceramic higher
wattage resistors and I found the same issues mentioned to you in a earlier
email with board thru plating. The whole size should have been a few
thousands larger than supplied even with vacuum de-soldering, as I used, you
may loose the thru plating, and this will result in display intermittants if
the both the top and the bottom of the resistors aren't soldered to restore
the connections. 
I also built a removable fan and shroud that slips over the heat-sink which
runs slow and quiet when the heat sink reaches 110 degrees F. I used a
normally open adjustable temperature switch found in commercial dryers which
has mounting tabs and will handle about 20A...a bit overkill, as the fan
draws about .1A @ 120VAC.
I hope you have as much fun bonding with your Signal One as I have, good
luck.

John
WB6DAX

-----Original Message-----
From: signalone-bounces at mailman.qth.net
[mailto:signalone-bounces at mailman.qth.net] On Behalf Of EDWARD SCHUMACHER
Sent: Sunday, March 14, 2010 3:08 PM
To: SignalOne at mailman.qth.net
Subject: [SignalOne] CX-7 Display

This list is for discussions regarding collecting, repair, use and sale of
Signal/One radios and accessories. 

Documentation on Signal/One radios can be found at http://www.hamanuals.com
and several other sites on the Web. 

.
Congrats on finally acquiring your Signal One, Rodger! I too ended up with
one a few years back, from the estate of one of the old DX'ers from my first
radio club no less. Be advised, changing the display to LED's will require
adding a resistor to stabilize the power supply because the nixies provide a
continuous load for the 300v supply. See the archived newsletters for the
details. 

I had some minor troubles with mine due to something having been spilled
into the display board that left dried residue under the ic's. I had to lift
each one, clean the socket and the reinsert the IC. This was when I found
the corroded off lead on one of the driver ic's. The good news is that
Mouser still has the chips and they are cheap! I also lucked out bigtime on
my one and only trip to Dayton year before last and found a guy with a small
box of nixies that turned out to be the correct ones for the CX-7 and also
very reasonably priced. I could not believe finding what I thought would be
next to impossible from my wish list for spare stuff for the rig. I got
several so you can bet I will probably not need them, HI!

I was very fortunate in that my rig had been well cared for and had none of
the issues with the PTO's but some of the other things I had to solve more
than made up for it. At least I finally upgraded some of my bench equipment
so I guess that's good. Hope to hear your rig on the air one of these days.

73 ... Ed, WA9GQK

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