[R-390] R-390 VFO Question

[Jacques Fortin]

I never had a single problem adjusting the endpoints in all the PTOs I have (7 in all: 6 Collins -including the R-390 Ver 1- and one Cosmos)
The work is way easier when they are adjusted stand-alone, btw.
I made the required power plug(s) and dial and all went smoothly, using a frequency meter on their outputs.
No need to use two different HV power supplies for the R-390A ones: almost no difference in output amplitude when the oscillator plate is powered with 150V dc.
I use an old (rebuilt) Heathkit IP-32 for the supplies.

I also found the procedure I used:

1_ Adjust PTO output frequency at 2.455000 MHz on the frequency counter and note the dial position (see attached "label" .pdf)
2_ Turn the knob COUNTERCLOCKWISE 10 full turns, stopping on the SAME DIAL POSITION than the one that gave the 2.455000 MHz output.
3_ If the frequency meter displays 3.455000 MHz, everything is perfect and the endpoints are perfectly aligned.
4_ If not, use the L701 adjustment to bring it at 3.455000 MHz
5_ Turn the knob CLOCKWISE 10 full turns, and adjust the output frequency to 2.455000 MHz.
6_ Expect that the dial reading for 2.455000 MHz have changed (depending if the endpoints were to close or too far apart initially).
7_ Go to step 2 and loop again: both endpoints will give the same dial reading after 3 or 4 iterations.
8_ Leave the PTO output adjusted at 2.455000 MHz and re-install it in the radio, taking care of properly adjusting the Oldham coupling disks position (counter at 07 + 000).

BTW, I still have two fully rebuilt and adjusted 70H-12 Collins PTOs in excess to my needs.
If anyone want one of these as spare, please contact me privately.

73, Jacques, VE2JFE in Montreal
-------------- next part --------------
A non-text attachment was scrubbed...
Name: R-390A-PTO-label.pdf
Type: application/pdf
Size: 122941 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/r-390/attachments/20240918/3d61ba90/attachment.pdf>