[Milsurplus] Radium, X-Rays and RCA

[Ray Fantini]

Couple thoughts about radium and x-Rays, I have owned and operated a TBX-6 including a couple times at Dayton during the WW2 AM Net and found that to be a great radio. Never owned or used a TBX-8 but somehow like the clean signal tube transmitter of the 6 along with its simple suppressor modulation system although it does require a microphone with lots of drive. I built a modified carbon microphone with a one transistor amplifier that was driven by the bias to provide lots of modulation. Also loved the receiver with its 34 tubes and that it only drew around 10 Ma during normal operation and the filament rheostat was fun for setting the filament current for the receiver. Think I only used a couple D batteries and ten nine-volt cells for the receiver and it would run all day long from that.
Although I never owned one so just going be speculation the 8 just don't appear to have the same charm as the earlier sets with its newer tube line up and T/R relay.
Radium behind meters don't appear to be an issue unless the glass is broken or if you disassemble it but the "hottest" radios I ever came across were the TBY sets being they had all the controls labeled with radium laced paint and just playing around with a Alpha detecting Giger counter can see a reading from a TBY across the room where you would have to get right up next to the meter to get a reading from a meter with glass intact.
Recall at least one story of where a TBY set off radiation detector at a land fill so that one set I don't want to own.
On the subject of TV and radiation before RCA went to controlling the HV for the big color TV sets of the late sixties and early seventies by regulating the horizontal output they did use 6BK4 tubes on the output stage of the HV supply to shunt regulate the 25 kV supply and back when I was a kid I worked in a TV shop and remember replacing flyback transformers in a number of huge heavy RCA sets CTC sets, think the CTC-16 may have been one of the last sets to use shunt regulation. That tube lived back behind the box that shielded the flyback in its own little enclosure that always had a warning sticker about the radiation.
At that time, it was common practice to pull the chassis from the customers set that was most often a huge wooden counsel and run the chassis on a test jig back at the shop that had a picture tube and deflection yoke so all the guts were right out in the open so you can work on them. That allowed you to look directly in and watch the strange glow of the 6BK4
All those huge RCA sets suffered flyback failure at a high rate. Later manufactures started using HV tipplers in the HV stage and flyback failures all went away but all that first-generation color stuff just used a flyback to develop the HV and back in the days when not everyone had air conditioning and high humidity those old transformers use to blow like fuses.
Last note if you're still reading, on those old RCA sets they had huge power transformers that ran most of the set. Modern TV sets derive most of the operating voltages from the Horizontal stage (Scan Rectification) but back in the old days a conventional power supply ran just about everything in the TV so when the flyback transformer shorted out the set would still have sound so the customer would still keep the TV turned on to listen to it but what would happen is that the Horizontal output tube would have a heart attack because it was driving a resonate stage, the flyback but now that's our of resonance so the output tube usually a 6LQ6 or the like would suck excusive plate current and turn red and after a while the envelop would weakens and burns a suck hole in the tube.  So you ended up hitting the customer up for a service call, new flyback transformer and a new H output tube and think the list price for those tubes was around $25 in nineteen seventies money, the customer would be out well over one hundred bucks to get that huge TV repaired.

Ray F/KA3EKH

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