Posted by Sherman in Idaho [72.47.153.112] on Saturday, March 01, 2014 at 14:16:06 :
In Reply to: OT; Speaking of Car Radio's Found this posted by Tom Petroff (IL) [64.12.116.207] on Saturday, March 01, 2014 at 04:46:23 :
I didn't know any of that. I suspect the reason the first radios needed their own batteries was for the plate voltage, which was 135 volts at an absolute minimum. The invention that no doubt reduced the cost and installation time a lot was the "vibrator", which used a vibrating contact like in a Model T spark coil to produce AC that would go through a step-up transformer to generate the plate voltage. All the old tube-powered car radios have vibrators, and they're a common source of trouble.
Another problem they had so solve early on was vibration shaking the tubes loose form their sockets. To do that they invented a new tube base called "loctal" (locking octal) which was metal rather than plastic and had grooves cut around the pins so they would snap into their sockets. Loctal tubes gennerally had innards corresponding to exising octal tubes, and their numbers were the same as the corresponding 6 volt octal tube, but with the "6" changed to a "7", so for example the loctal version of a 6SN7 would be a 7SN7.
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