This next item is not just a piece of radio history, it is a piece of local radio history. Local being Edmonton, Alberta, Canada.
It’s a crystal oven for a broadcast transmitter. I don’t know what years it was in use but given the frequency of 930 kHz it is a virtual certainty that it was used at a local AM broadcast station, CJCA, which has operated on that frequency from 1935 to this day.
CJCA was, in fact, the very first radio station here in Edmonton starting in 1922. And there is a personal connection for me as my grandmother Hazel worked for them in 1922 (they were on another frequency then) when they were starting up operations in an unheated shack on the roof of the Edmonton Journal building in downtown Edmonton where she worked as a stenographer.
I picked this unit up at an estate sale of a long term and avid collector of vintage radio equipment. It’s in perfect condition. It was made by Bliley Electric Company of Erie, PA and bears a model number of BC-46 on the metal plate on the top and BC-46T on the label affixed to the side of the unit.
Here’s a picture of the top plate showing the frequency of the crystal inside and the specified over temperature of 52C.
The next picture shows the front of the unit where you can see the thermometer showing the oven temperature and a label indicating the oven power supply specifications of 10V @ 1A.
When I stumbled across this device and noted the frequency I knew that I should acquire it and preserve a piece of local radio history. I was curious to find out if it still worked and the first step was verifying that the oven still worked.
I hooked it up to my trusty HP power supply and dialed up 10V DC. I noted that the unit was drawing 900 mA of current. After a few minutes the mercury in the old thermometer (and it’s silver, not red, so that may help to date this thing) started to rise and the ceramic housing felt warm to the touch! Several minutes later it was sitting at 50C.
There’s the test set up. Amps on the left meter and volts on the right. I noted that the temperature rose to 50C and then the thermostatic control circuitry inside this little gem kicked in. I observed the heater cycling on and off to maintain that temperature. The first functional test had passed!
The unit has a base that plugs into the old five pin tube sockets. The same type used by the 807 triode and others. At some point I shall have to build a test platform for it. I am envisioning a small metal box with an oscillator circuit, terminals for external power and RF out with a socket on top to plug the module into. If and when I do that I will document it here.
When I was a young boy in the 1960’s my grandmother always had CJCA on her Simpsons-Sears table top vacuum tube radio on her kitchen table. I ate many meals at that table with CJCA tuned in and warm audio coming out of the old radio. As an adult I listened to CJCA after they switched to a talk radio format. In the mid-1990’s they switched to broadcasting religious rubbish and they are no longer fit to listen to.
But there was a time when CJCA was the king of the AM airwaves here in our good city and so I shall keep and preserve this device. I love the old technology and also the cutting edge. It’s all wonderful stuff!