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Counting on radiation history

Posted: Wed Aug 17, 2016 8:46 pm
by Richard Hull
Most here can pick up a decent counter used on e-bay for about $50.00. It will be modern, based on IC or CPU technology. Its display can be LED, LCD. It might be battery powered or use just 20 watts from a wall outlet.

History was not always so kind to the radiation counter enthusiast. As a matter of fact, no amateur enthusiast could afford a counter until the early ones went surplus in the 60's or later.

I recently acquired and restored a Berkley Scientific, 7 decade counter from the late 40's, early 50's which, at the time, was about the same price as a new Ford automobile!

I attach images with text in them for your edification.

The 53 pound unit cost me $1.00 at a boat anchor table at the Berryville hamfest a while back. The fellow who sold it to me noted that it was $1.00 if I carried it off or he would have his son take it to my van for $5.00 more. I opted for the $1.00 and football field distance carry on my own in the 96 degree heat. (about my current limit at 70 years of age.).

The unit originally had 58 vacuum tubes in it. On the main chassis all the tubes were still present, but the (28) 12AX7 equivalent 5963 dual triode tubes in the seven decade boxes were all pulled and missing. (sold, I am sure, to the hungry audiophiles who treasure and pay dearly for them.)

I easily found the schematic for the Berkley decade boxes on line from a google search!! It seems these Berkley 4 tube decade boxes are currently in high demand by retro-electronics enthusiasts who make up solid state electronics to drive these retro displays.

At home, I cleaned the unit up, made it look pretty, replaced 4 old power electrolytic capacitors, took it up on a variac and it drew just over 2 amps, well within its 500 watt nameplate rating, (of course it was missing 28 tubes). So far so good. The GE essential characteristics tube manual noted that there were about 16 different tube numbers with the same base as the 5963. Among them were 12AX7, 12AU7, 12AT7, 12AV7, 12AZ7 and many, many others in the 4 number codings.

I accumulated about 10 tubes that were in my own personal stock and got the units and tens decades counting. A friend who is a tube freak has a collection of 3-5 thousand tubes and allowed me to look through his 12 volt loose, unboxed tubes. I found about 55 possibles which he allowed me to take home. This allowed me to completely re-tube the decades and, after replacing 2 more capacitors in the 5th decade, all is well. I returned the unused tubes to my friend. He told me that since they were not boxed I could have them at no charge! Great! (Dodged that bullet!). At hamfest prices I would be looking at $50-$150.00 to re-tube those decades.

Interestingly, not one single 4 tube decade has all tubes of the same number in them....A mish-mash of 12Axx numbers.

I spent about 3 hours tuning up the unit, adjusting the crystal oven to it nameplate rating after a 1 hour warm up. For those not in tune with old technology, the way to skin the decade step down cat on frequency, (100khz to 10khz to 1 khz to 100 hz to 10 hz to 1 hz) , was to use a single tube tuned multivibrator. Today we just use divide by ten chips with 4 flip-flops to get a locked in, no tune needed, divide by ten. I adjusted the pots for these multivibrators seen in the tube view image, attached.

Compared to my 50 mhz HP counter, this puppy is right on the money!

I plan on using this old relic as a winter counter and space heater as it now pulls the rated 500 watts from the wall outlet to count nuclear pulses. Cool beans.

As usual, for a stunning close up, click on the images.

Richard Hull

Re: Counting on radiation history

Posted: Thu Aug 18, 2016 3:21 am
by Bob Reite
I had one of those! Back in 1976 I actually used it to check the frequency of VCR servos back in the day. I also had a Heathkit prescaler that had a divide by 100 setting, I think I was able to get up to 2 meters (144 Mhz) with it. I sold it to someone when I got a Sencore frequency counter that was a lot more portable.

Re: Counting on radiation history

Posted: Thu Aug 18, 2016 6:40 am
by Richard Hull
My serial # is 173, so it is an early model. I assume this was made rather continuously until transistors took over and morphed into different displays as well. Transistors were nefariously weak and unreliable until the late 50's and tubes were still used all through the 60's in critical gear. The last tube units disappeared in the early 70's. I have never seen a Berkley nixie unit. I do have a Baird Atomics 5 dekatron counter that uses vacuum tubes circa 50's as well. I have a small collection of early Nuclear Chicago gear that I really cherish. They were big in both industry and educational, classroom radiation counters. They stayed with tubes into the late 60's

Richard Hull