The Mississippi Historical Radio
and Broadcasting Society

Vol 7 #1

September 4, 1998

News Letter

Well, the Annual meeting came and went. Less than 25 "collectors / club members" showed up and only another 30 or so "general public" coming through - made for very light attendance - far less than any year before - but since it had been two years since the last "big meeting" - and I wasn't able to promote it as well as I have in the past - I guess that wasn't too unexpected. Then again - we also got "hit" with some pretty bad luck. Our Vice President - Bill Gerk had something come up - so he couldn't attend - as did four other club members - who all had called and expressed their disappointment. One of the groups who usually come over from the Atlanta area called - and one of them had a death in the family - and the rest decided to go to a HAM fest that was much closer...

On the other hand - we've had five new people join - and a double handful renew-- so I guess the club isn't dead - just suffering from "couch potato-itis" like so many other small clubs. On the other side of the coin - the weather was fabulous, the food was great (BBQ ran all day) and there were a lot of radios for sale / sold in spite of the light turn-out. Sherry got an ART-13 - she's wanted one to go with her BC-348R for a long time... and I sold a good many radios and pieces of test equipment. We did have some people in from the Gulf coast - and Memphis... (and at least one member of the Alabama club)... and though they didn't say much... I couldn't help but feel they must have been disappointed in the light turn-out - though everyone seemed to express that it was a nice show in spite of that. Maybe next year will be a lot better attended - We haven't set a date yet - but Highland Park proved to be so popular - we're going to do it again next Spring.
Newsletters. I'd hoped to get the Newsletters back on a monthly schedule - but with the current demands on my time as they are - it looks like quarterly is going to be the best I can do for the time being. Of course - anyone wishing to help out / or take over would certainly be welcome and have my gratitude.
Radio Collecting Today

One "group" of radios that has never enjoyed much favor with collectors are the small 40's batterysets that were very common in rural America. Using large and expensive "AB" packs - which haven't been available for a long time - these sets weren't considered by many collectors to be worth the effort fix them up. As electrification came to rural areas - some of these radios were converted to work off the AC mains via a battery eliminator - a small power supply that contained a power transformer, rectifier and filter circuits to replace the expensive battery. These are not real common today - and few meet modern safety requirements. So collectors tended to just avoid these battery sets - preferring the self contained AC models.

But times - they do move on! As AC sets become harder and harder to find - some collectors are "revisiting"the battery sets - and need a way to power them. Problem is - eliminators are fairly rare - and appropriate power transformers to build a power supply are next to impossible to find - at least at a reasonable price.

Parts List for 1.5V filament and approximately 90V B+
	T1120V Pri. 12VCT 1A sec. T2120V Pri. 12V 300ma sec. D1 - D5 > 400V 1A C1, C2 30ufd 150WVDC C3 1000ufd 16V C4 .1 ceramic or 1ufd Tantalum C5 4.7ufd 15V R1 250 Ohm 1/4W R2 47 Ohm 1/4W R3 240 Ohm 1/4W

Looking at the schematic - you can see how we solved the transformer problem. Since the average battery set uses less than 20ma. B+ two filament transformers wired back to back (i. e. secondary to secondary) will provide somewhere between 90 and 110 volts at usual working current (after rectifier and filtering). Tapping off of the secondaries with a full-wave bridge, filters, and an LM-317 regulator IC - a very accurate and stable 1.5V filament supply is provided.

You can get almost everything for this supply at Radio Shack (except the B+ Filter caps.) - or a well-stocked junk box. Radio Shack doesn't have 6V transformers - so the parts list shows 12V units. But any voltage can be used between 3V up to 24V - higher might exceed the 317's maximum rating - just so the secondaries are the same voltage. There doesn't have to be a center tap - it just so happens the Radio Shack 1A transformer has a center-tap - so it's used just to improve efficiency.
Don't use a larger value cap for C5 - it might cause a turn-on spike that would be un-friendly to the filaments. In fact - you can leave it out all together - it improves the 317's ripple rejection by roughly 40db - which is a bit of overkill for a filament circuit.

This circuit can be adapted - for use with older sets if desired. Change the value of R2 to say - 380 Ohms (330+51) - and it will power a UX/UV199 set. The calculation for R2 is the standard formula for the 317: Vout = 1.25(1+(R2/R3))+(.0001(R2)).

By using a beefier T1 - (say 12V at 6 Amps), beefier diodes and a different regulator (say an NTE 932) you now have a power supply that can supply a battery set using a flock of 01's... be sure and use the full 12V secondary - rather than the center tap.

Whichever regulator you use - be sure it has enough heat sink to prevent overheating.

As shown in the schematic, the power supply uses so little power that it can be left on all the time - and the radio's switch used to turn the set on and off. If a "beefier" supply is built - a power switch on the supply itself might be added.
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{as the calendar of events is not reproduced here - as it quickly becomes outdated.}

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