A New Battery Pack for the old GR-78

Figure 1: A new Battery Pack can be seen tucked into the old Heathkit GR-78 (left of photo).

So, I’ve been tinkering with the old GR-78 for a few days.  I mentioned in the last post that the old NiCad battery pack was completely dead (not surprising in light of its age being over fifty years).  I tucked a new NiMH battery pack into the GR-78 enclosure, putting it on the opposite side from where the original NiCad batteries were mounted.  The reason for this change is that I want to use the space on the inside of the chassis wall for mounting a small Qrp transmitter!

I haven’t figured out what type of charging circuit I’m going to use to charge the NiMH batteries, but probably won’t try to use the existing circuit for the purpose.  Meantime, the current draw on the new pack is only a little over a hundred milliamps when using headphones.  With the 2500 mAhr rating of the NiMH batteries – that should give me somewhere around twenty or twenty five hours of continuous operation, depending upon how far I want to discharge them.  A small Qrp transmitter won’t add much to the load, especially because it’ll be so intermittent.

What to use for the transmitter?  I have a slew of 2N2222s LOL – maybe I should fashion something with those!

To be continued …

Note: the author is not a battery expert, so these pages are presented as the work of a hobbyist, and are not meant for duplication by others. Readers should look elsewhere for design advice and info.