[R-390] R390 PTO endpoint

Wed Jun 12 20:02:15 EDT 2019

I came up with a simpler method once I learned where the EP adjustment screw
was hiding.  The R390 and R390A has everything you need built-in: no jigs
needed.  Calibration oscillator, a 10-turns counter, etc.  So, it's very
desirable to be able to do the adjustments while the PTO is in the radio.
Problem is, with the R390, the front mounting bracket for the PTO blocks
access to the adjustment screw.  To get around this and not have make any
funky tools, I just made up a simple surrogate bracket to use to set the
endpoint.  Made the bracket last night, installed it and had my PTO endpoint
set in less than 15 minutes this AM.  Add another 10 minutes to reinstall
the OEM bracket, reinstall the block plug, and reinstall the PTO.  Came out
once and back in once.  With the surrogate bracket, the endpoint screw can
easily be reached with a small screwdriver.

*I have a mechanical drawing for the bracket I made if anyone is
interested.*  You can make it with a vise, a hammer, sheet metal shears, a
drill press (maybe even a hand drill), and careful layout with a machinists'
scale (ruler).  See attached pic...  This was done on my Bridgeport mill but
it didn’t have to be.  I have two versions of the drawing: fractional inches
and decimal inches.  If you want a copy let me know your preference (as a
home shop machinist I prefer decimal and hate fractional)

I didn't use the cal. oscillator since I have a very accurate digital
frequency counter, but the calibration oscillator could be used instead.  My
PTO was very well linearized thankfully, but the endpoint was off about 6
kHz.  It came right in with adjustment alone and no endpoint coil turn
removal.  I'm glad of this because my R390 PTO remains factory sealed.  My
R390A was another story...  The R390A needed a turn removed, linearization,
etc.  Thankfully it's a Cosmos so linearization is not too bad to do.

Basically, when adjusting the endpoint, the start point changes too, so you
need to go back and forth a few times to get it spot on.  You zero the dial
at the low end and dial up to 3.455 and make adjustments at the high PTO
frequency which is the low end of the dial.  Go back to 2.455, re-zero the
dial, go back to 3.455 adjust and repeat until both ends are 2.455 and 3.455
kHz.  Easy.

-----Original Message-----
From: Lester Veenstra <m0ycm at veenstras.com> 
Sent: Wednesday, June 12, 2019 4:46 PM
To: jgedde at optonline.net; r-390 at mailman.qth.net
Subject: RE: [R-390] R390 PTO endpoint

http://r-390.com/pto.htm

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y
lester at veenstras.com

452 Stable Ln (HC84 RFD USPS Mail)
Keyser WV 26726

GPS: 39.336826 N  78.982287 W (Google)
GPS: 39.33682 N  78.9823741 W (GPSDO)

Telephones:
Home:                     +1-304-289-6057 US cell                   
+1-304-790-9192 Jamaica cell:           +1-876-456-8898 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of jgedde at optonline.net
Sent: Monday, June 10, 2019 4:29 PM
To: r-390 at mailman.qth.net
Subject: [R-390] R390 PTO endpoint

I've started to look into doing the PTO endpoint on my R390.  The PTO is
completely different than the Cosmos one on my R390A which I was successful
in calibrating, including linearity.  Where is the endpoint adjustment on
the Collins R390 PTO?  I can barely see a plug behind the transformer can.
Is that where it's hiding?  

My PTO also has a plastic plug screwed into a hole marked S701.  Behind the
plug is a hollow shaft with two notches to allow it to be turned with a
screwdriver.  What is that for?  It does nothing as far as varying the
frequency.

There is so much wealth of information online about the R390A and its
various PTO flavors, but not much about the R390 PTO.

73's,

John

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