[Chris Cusick]

Hi - I am getting ready to restore one of these farm sets and I was curious about the best arrangement for replacement batteries. I think the B voltage is OK, but this radio needs a 1.5 V supply for the tube filaments. That's a lot of current draw. What works well ? I was thinking of multiple C or D cells in parallel but I'm not sure how many I would need to give me a decent operating life (maybe an hour a day for a month or 2 ?)

All thoughts gratefully received

[tom.seeger]

I have used 2 alkaline Ds in parallel, and 10 alkaline 9V in series on a G.E KL-4B farm radio and they have been playing strong for at least 10 hours in 30 minute plays.
Tom

[BrendaAnnD]

The current shouldn't be too bad. Most of those 1 volt tubes run about 60 mA. If your radio is typical, it's got four tubes, so just under a quarter amp. Half dozen alkaline D cells should last quite well.

[Radioroslyn]

That's a good question. I guess the good thing is the D cells are pretty cheap as you can get 2 for a buck at the Dollar store. It might even be 4 for a buck. Unfortunately I don't know of a holder that is wired in parallel most are wired in series so you won't end up with 1.5v in the end. I guess you could rewire the filament in series but most of the time the output tube filament is rated at a higher current than the rest so you'd need to put in a resistor to balance the current.
GL
Terry

[Chris Cusick]

OK - Thanks for the ideas - I'll aim for 6. There are 5 tubes in this one - it has a push / pull output. It's more of a challenge to wire things up in parallel than series - as long as there is enough room, I plan to get 6 x single D cell battery holders and wire those up in a 'ladder'. I have a goodly supply of D's that I grabbed from my local Menards store when they were on sale. The B supply will probably be 10 x 9V batteries snapped together, just because that's so easy to do.

[Radioroslyn]

I've always been interested in how much current you a can get out of a 9v battery. I think an average shirt pocket xsistor radio pulls about 10 to 15ma.
Terry

[Chris Cusick]

I think I saw it was about 500 mAh. I know that I can get a nice long service life using 10 with 'brand Z' portable sets so I'll go with that. I also tried 60 AA batteries but that is seriously heavy to carry !

[tom.seeger]

Well by my calculations your radio should draw about 0.25A from the 1.5V battery circuit. A single alkaline D cell should provide about 8 Ah. Thats about 32 hours of play time.
The B supply draw should be around 10 mA at moderate volume. A set of 9V alkaline batteries should provide about 500 mAh. Thats about 50 hours. These numbers are approximate of course. Its hard to tell how the radio will work as the batteries approach the end of their lives.
But it does show that there is really no need to build a 4 cell A battery pack.
My farm radio is still going strong after about 2 months of listening several times a week for 30-60 minutes.
Good luck with it.