Several weeks ago, I posted a problem with the 9 MHz oscillator in my TR-4 could not be gotten down quite to 9.000000 MHz. At the suggestion of a list member (one of the Garys?), I placed a 2pF across the trimmer and that resolved the problem. I didn't really like leaving it that way as it makes the rig a bit less original.
I ordered a small assortment of 9 MHz crystals from Mouser. Two were parallel resonant and one was a series resonant. I had read where that oscillator should take a series resonant crystal, I tried it first but that crystal resulted in the oscillator being at least 1 kHz high and it appeared I'd need on the order of 30pF or 40pF extra to get it working (even if it could be "pulled" that far).
With all the talk recently regarding baking crystals, I gave it a try. To be a bit on the safe side as I didn't have an accurate thermometer, I set the oven to 330F and baked it for three hours. I reinstalled it in the rig and, without the extra 2pF capacitor, I can easily get it to 9 Mhz now. Nice!
Thanks,
Barry - N4BUQ
