[MRCA] GRC-9 Receiver Bias Battery, replacement

[Ulrich N Fierz]

Hi all,
there are - as mentioned - quite a number of solutions. I would like to add two optically nice ones I've considered and one implemented:

First you take out the old battery (which is held by a clamp - see later) and carefully saw the plastic about 1-2mm above the lower end (thus preserving the pin base). Then you can remove the contents which in my case (TELEFUNKEN made) were 3 NiCd cells in series and a plug to fill the remaining space. Yours might be different.

Solution #1 is to procure 3 NiCd cells of the same type (with solder lugs, still available from distributors) and install them as before (I did not choose this route). If you do, charge them initially the recommended 14h @ C20 away from the radio to prime them.


Solution #2 is to use a CR123 Li battery which fits the inside of the plastic tube. The two wires (or rather flat strips) from the pins are used to contact the battery. The + is formed into a contact (with a cardboard insulator between it and the pins) at the bottom and the - threaded along the battery to connect at the top. I did not use soldering but inserted a suitable diameter spring into the plastic case. Now the assy can be carefully moved together, plugged into the socket and - see the clamp above - the clamp fixed while the spring is despressed to allow good contact of the metal strips to the battery. That's what I've successfully used and tested.


Two comments:
- you don't have to use a very fresh CR123 as current draw is nil (actually grid current against the battery volts while the radio is turned on - that's what was used to charge the NiCd elements).
- there are now just over -3VDC on the grid of the AF power amp rather than the recommended -4.5VDC. The radio sounds ok though and the additional mA do not hurt as long as you do not use an anode battery.

Good luck and remmember: YMMV

73,
Ulrich  hb9aik - vk6bqd

 
Ulrich N Fierz
Telecommunication Engineering Services
Zurichbergstrasse 203
CH-8044 Zurich
Switzerland
<hb9aik at yahoo.com>



>________________________________
>