Intriguing unit

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.

Tubes now in a box. Intriguing unit on top.

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 🙂

Dead tree resources

LA4FK appears to have been a well organized person. With the set came a ring binder with instructions, notes, receipts, copies of articles etc.

Binder with notes and more. Picture shows notes and schematics for a VFO. It is not known if LA4FK ever built that one, but apparently he went far in preparations. Background shows a radio glossary and a textbook on radio building.

A lot in it does not seem useful. A few things works as useful pointers in the restoration work. There is very little in there that is material for the blog. Except perhaps a couple of things. Something in there was a puzzle for me. I think I shall make a puzzle for you to solve. In a future blog post.

Two books were also included. There have been some development in technology since these books were published in the 60’s. Some fun tidbits found anyway. I found one curious little thing to write about there.

No trees were harmed in the writing of this blog post.