[SignalOne] CX-7A repairs

[Singley, Rodger]

I finally finished repair work on a CX-7A I picked up last summer and made my first contact with it today.  When I bought it the rig was in good cosmetic shape but in unknown working condition.  It came with a homebrew CW filter in the CW-2 slot, power cord, a couple of spare finals, and manuals.

The power supply board had been upgraded to use 3 terminal regulators and I found that the 7805 had been installed without the recommended dropping resistor so I added that and also took care of some ugly connections.  The meter lamp was broken so I installed 3 LED's in series along with a dropping resistor from the 15 volt supply.  To fit properly, the top of the LED's must be cut off (I used a cutoff wheel in a Dremel tool) and this also diffuses the light.  Initial power up resulted in both the receiver and transmitter working but with flaky operation from both the A and B PTOs.  

The A PTO ceramic coil form had cracked where it mounted to the front plate so I used some epoxy to repair it.  I expected to find the same problem with the B PTO but instead the glue holding the core/ceramic guide had come loose from the metal guide disc so it also required epoxy for reattachment.  I checked the same part of the A PTO but it shows no sign of coming loose, that will probably happen next week :) but at least with redundant PTOs the CX-7A would still be usable.  I also cleaned and lubricated the PTOs while they were out.

The only remaining problem is with the counter/NIXIE display.  The tenths digit always displays a weak 4 in addition to whatever number it should display so I need to sort that out whether it is a chip or the display tube itself.  Beside this problem, after a slight alignment touch up and check of the adjustable oscillators the sensitivity is fine and it is producing rated output in both the bandpass and manual tune positions.  Next step is to interface the CX-7A to an Alpha 274 I picked up a couple of years ago.

I first saw a CX-7 when I was a novice in 1975.  A member of the local club on the MS gulf coast had one and brought it to the club meeting one night.  A most impressive rig to a 14 year old novice and really no less impressive today.  I am glad I finally ran across one at a hamfest.  Just prior to this I finished restoration of a 1932 Hammarlund Comet Pro so this was quite a technology shock!

Rodger WQ9E