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Jon_G4MDC · 29th Jan 2023, 12:28 pm

The TR2200 was a well known crystal control rig from the 1970s.
It went through a few different revisions the last of which was the GX which had provision for an external VFO as well as crystal control. I had one as my first rig in 1977 or so.

It has always puzzled me that they had no frequency adjustment for the RX crystals. They just said buy the genuine ones from a Trio dealer or they might come out off frequency. They are 45MHz third overtone types.

Today I thought I might look into the oscillator to see whether it would be possible to add some adjustment. Crystal availability being what it is I wondered if anything in the junk box might be useful for an extra frequency or two. A pulling coil might be useful.

Now I look at the oscillator circuit it doesn't make sense to me. I expected to see a Colpitts. Well is isn't. Does anyone recognise how that works? The diodes for the VFO/XTAL switching are clear enough. I can see it would work OK with VFO input but I can't see any feedback to make the crystals oscillate.

Any ideas please?

29th Jan 2023, 12:28 pm	#1
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Trio TR2200GX RX Oscillator The TR2200 was a well known crystal control rig from the 1970s. It went through a few different revisions the last of which was the GX which had provision for an external VFO as well as crystal control. I had one as my first rig in 1977 or so. It has always puzzled me that they had no frequency adjustment for the RX crystals. They just said buy the genuine ones from a Trio dealer or they might come out off frequency. They are 45MHz third overtone types. Today I thought I might look into the oscillator to see whether it would be possible to add some adjustment. Crystal availability being what it is I wondered if anything in the junk box might be useful for an extra frequency or two. A pulling coil might be useful. Now I look at the oscillator circuit it doesn't make sense to me. I expected to see a Colpitts. Well is isn't. Does anyone recognise how that works? The diodes for the VFO/XTAL switching are clear enough. I can see it would work OK with VFO input but I can't see any feedback to make the crystals oscillate. Any ideas please? Attached Thumbnails Last edited by Jon_G4MDC; 29th Jan 2023 at 12:33 pm.