Did I find gold? Read on to find out!
The set came with a bag of tubes. I didn’t have the time to study them, but one unit stood out. In blue metal can with white text.
Y201 and Y203 looks very much like crystal component IDs. 17.0 MC and 200 KC looks very much like frequencies of the respective crystals. 6.3 V happens to be a common filament voltage, including in the HR-10. Why would it need filament voltage unless there is a vacuum tube in there? Could this be a crystal calibrator?
The socket for the crystal calibrator in the HR-10 was empty. The original crystal calibrator for the HR-10 does not look like this, but it is conceivable that LA4FK had plans to adapt this one. That could be as easy as rewiring the socket. I was optimistic I had found something very useful. I would have to research what this is. Do you think I was on to something? Make up your own mind first. I’ll make a little but relevant digression.
The Collins R-390A/URR
The 1976 edition of the World Radio and TV Handbook is were I first saw the R-390A/URR. Looking like it belonged in a James Bond movie, the receiver was big, heavy, expensive but probably a good performer. It was hard to accept that any receiver could be better than the one I owned. An ad would never lie of course.
It was also the first time I saw the term “mechanical filters”.
For a long time Collins was a highly esteemed brand in radios. When their radio production faded they still kept on producing those magic mechanical filters for others. They were not at all inexpensive.
The R-390A lived on for a long time after it was technologically old. Not the least because the military was an eager customer. Many variants were made, like a lighter version for aircraft e.g.
A search on the Internet brought me to http://www.r-390a.net/Redux/01_Jan_03.pdf which contained the text “Calibrator Y201-17.0MC,Y203-200KC”. Note that this was a forum dedicated to the R-390. My heart started beating faster. Let’s keep on digressing.
I inventoried the tubes and found that many of them were used in only one product. The R-390A/URR.
I was told LA4FK had access to and sometimes brought home decommissioned radio equipment from his workplace in the military. It is not inconceivable that an R-390A could be among them. Seems he pulled the tubes and this blue thingy out of one.
To use it I had to find its pinout and other specs. My searching failed me but I kept on dreaming that I could get this crystal calibrator to work in the HR-10 with some modifications. After a few days I realized I could search for R-390A schematics and figure out the pinout from that instead. Took me seconds to find excellent copies of the schematics. I also found the Y203 et. al. in there.
So, did you make up you own mind about what this is?
Turns out this is a crystal oven with two crystals and a temperature controlled heater. The 6.3 V is for the heater. That also explains the “75°C” on the can. The 200 kHz (or 200 kC as they said in the old days) is indeed for a crystal calibrator. But all the active circuits are on a board in the R-390A. Not in the blue can. Sigh!
The 17 MHz crystal is for the first local oscillator.
Well, I learned a few things. Also, if an R-390A comes my way some day, I have spare tubes 🙂