[R-390] RF Alignment Questions

[Roy Morgan]

At 11:39 AM 2/27/2007, Carole White-Connor wrote:
>My R-390A is coming along nicely. I sounds great and is performing nicely on
>most bands. Now, I want to tweak the RF alignment on the 2 mhz and 3 mhz 
>bands.
>Here are my questions:
>
>1. According to the manual, I should set the bandwidth to 8 khz. Is that
>correct? I would think it should be adjusted more narrowly.

Joe,

The narrowness of the *IF* bandwidth doesn't make too much difference as 
you adjust the *RF* circuits.  Just follow the manual.

>2. The output meter is adjusted to the diode load. The signal generator is
>adjusted to give an output of -3 to -7 V. Is that on the -DC range?

The meter should be measuring negative DC voltage at the diode load.  Don't 
confuse an *audio output meter* with a DC measuring meter. The Audio Output 
Meter is used in other measurements on the radio (specifically signal plus 
noise to noise measurements.  You can use a VTVM or DMM set to measure AC, 
however, when you measure the audio output of the receiver.)

>3. Do I set the signal generator for modulated or unmodulated output?

Either, I would say. The diode load terminal will have a DC voltage 
proportional to the carrier of the signal.  It may be less confusing to 
have the modulation off.

>4. Would there be any great problem if I adjusted the slugs and trimmers 
>to WWV on the 2 mhz band and CHU on the 3 mhz band without a signal generator?

There may be a problem.  WWV is at 2.5 mc.  CHU is at 3.335 (or close to 
that) mc.  The alignment frequencies given in the manual are intended to 
allow you to adjust an inductor at the LOW end of a band and a capacitor at 
the upper end of the band (If I remember correctly.)  The WWV and CHU 
frequencies are likely not close enough to the top and bottom edges of the 
respective bands to be best.

You CAN use the calibrator signal to do the alignment of the RF 
stages.  Just pick a calibrator frequency close to the frequency called for 
in the manual for the alignment points.

Don't forget to set the IF Gain to something reasonable.  If that is set 
too high, you are apt to get misleading results.  The procedure is 
publicized well, but to be very quick about it: set audio and RF gain full 
up, short or load the antenna with a 50 or 100 ohm resistors, and set the 
IF gain pot to get a low but audible noise level.  Then later do it right.

One other note: make sure the correct tubes are in your radio, especially 
the 6DC6 in the first RF stage and the right tubes in the IF strip.  I have 
a 75A-4 in which some earlier owner substituted a 6VZ6 for the 6DC6 first 
RF stage. I certainly will back out any under-chassis changes he made and 
put the right tube in there.

Anyone who has done tube changes to "make the receiver hotter" has *NOT* 
done you any favors.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --