Golborne Vintage Radio

Hello,

I've just come across an old HCD Research oscillator - a HCD81 running at 10MHz.

As you'll see from the picture, pretty much everything I need to know is on the label. But with one exception - how to use the Vf input. I presume it'll be a preset between 5V and GND, perhaps with a series resistor, but I'd like confirmation first as it would be a shame to damage it.

The unit works quite well, but the output frequency is a few hundred Hz away from 10MHz, and it doesn't quite settle down - well, not in the 30 or so minutes I've run it for. The lash-up on the bench probably didn't help - just test leads, no decoupling or anything. Leaving Vf open-circuit probably didn't help.

I do have another one of these, running at 8.86MHz (guess where that came from ). That one has a 9V heater voltage - I guess these things were pretty customisable. As I'll never use it, I could open it up and reverse-engineer it, but I'm hoping that someone like Jeffrey will have used these in the past and might still have some data.

Thanks in advance,

Mark

I have used these in the past. Away this week so no access to data but from memory it's 0 to 5V adjustment. By oven standards they're nothing special. Typically about 0.2ppm so juzt right for a PAL SPG.

In the late 80s and 90s these OCXOs were about the lowest cost way to meet the PAL 1Hz subcarrier stability spec in an SPG. So several UK makers used them. Including Courtyard who were and still are my clients.

That 0.2ppm spec is very tight for a TCXO but very slack for an OCXO. The HCD81 wasn't cheap but it was still a lot cheaper than any other ovens. A modern digitally compensated TCXO can meet the spec at much lower cost. It's also tiny.

Thanks for that, Jeffrey. Slightly better than those lovely Golledge TCXOs, but it sounds like I could do better

I do have an ancient HP OCXO that is untested but likely OK. Must find the time to investigate further...

If you do come across a datasheet upon your return, it would be much appreciated.

All the best,

Mark

There's a data sheet on the Golledge site (http://www.golledge.com/pdf/products/ocxos/hcd81.pdf) which confirms the tuning voltage as 0.5 to 5v.

Good basis for a simple GPSDO a la James Miller? (http://www.jrmiller.demon.co.uk/projects...rqstd0.htm)

Jim

Brilliant - thanks, Jim

Yes, I really like the idea of a GPSDO. A bit OTT for my needs, but definitely "pushes my buttons"

Jeremy has built a nice one, and I've been trying to persuade him to post some details (hint, hint!)