[R-390] Capehart made R-390A Serial #312

[David Wise]

The 2nd xtal oscillator trimmers set amplitude (adjust for max), not frequency. Sorry if everyone knew this but it seemed like it should be said.

Dave Wise

> On Apr 10, 2025, at 11:42 AM, Jacques Fortin <jacques.f at videotron.ca> wrote:
> 
> Hello Karsten,
> 
> Can you explain how do you probe the oscillator output ?
> It is a connection to your frequency meter that use any coaxial cable ?
> What is the input impedance of the frequency meter ?
> 
> Sorry to ask, but maybe you did not figure the implications: if any
> additional capacitance is introduced in the 2nd crystal oscillator
> structure, this will add to the C431H in the V401 circuit, then probably
> preventing the oscillator to work on the 3rd harmonic of the crystal.
> BTW, to answer a question asked by Larry Haney, the 31MHz band probably
> works OK and that is because the stage works in doubler in that band (2 x 17
> MHz).
> 
> Are you trying to "tune" the Xtal outputs to the "right" frequency by using
> the frequency meter, or did you use it just to confirm that the oscillator
> is working on all ranges during the alignment process ?
> From the Y2K-R3 alignment instructions, nothing specifies to do so.
> The "trimmer adjustment"  instructions in the section 6.2.9 should be
> followed without connecting anything, except the 2nd mixer, to the 2nd
> crystal oscillator output !
> 
> 73, Jacques, VE2JFE in Montreal
> 
> I am currently working on realignment: checking and tuning Crystal
> Oscillator subchassis. Frequencies measured with an accurate  8-digit
> digital counter. Everything appears to be ok. One exception: oscillator
> output on band 30 is 22 MHz (2nd harmonic), should be 33 MHz (3rd harmonic).
> Active crystal is Y403 (11 MHz). Trimmer capacitor C431H appears to be ok.
> Output (pin 3 of T401) is in the range of 3 to 5 volts and can be adjusted
> by turning C431H. Band 8 (11 MHz osc. output) is ok. Band 19 (22 MHz osc.
> output = 2nd harmonic) is ok. Any ideas why band 30 output is 2nd harmonic
> and not 3rd?
> Regards
> Karsten
> 
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