[Collins] 75A-3 Collins Recv'r

[Al Parker]

Hi  Joe,
	Your PTO can be slipped to center it's error.  To center it, set the 
readout in the center, then loosen the PTO coupling's shaft setscrew and 
move the PTO itself to zerobeat the proper calibrator signal.  But, it 
is still 11kc off in "span", and you'll be barely able to adjust the 
indicator enough at the ends.  The PTO should be removed and internally 
"tweaked" to bring the end to end span back to zero error.  The 
procedure isn't difficult, probably getting it removed and back in is 
the hardest part.  You can see some of the work I've done on them at 
<http://www.boatanchors.org/75A2.htm>  Similar work is shown in the 
R-388 pages.
	The higher band crystals will have lower output than the lower.  The 
output is adjustable by band, see sec. V-6 in the manual to optimize 
things.  Basically, as long as they're oscillating, you are in business, 
a more negative reading might improve things slightly.
	I think what you're seeing for the var. IF is normal.
	It sounds like you've been thru much of what needs to be done, and you 
have it working nicely.

Al, W8UT
www.boatanchors.org
www.hammarlund.info

"There is nothing -- absolutely nothing -- half so much
worth doing as simply messing about in boats"
Ratty, to Mole

On 12/29/2011 11:28 PM, Joe Walden wrote:
> Hello,From Joe w5jdy in Okla...  The last time I posted here I was looking
> for help with a 75A-3.  This time I have a couple of questions concerning
> the same receiver...   Can anybody help me with these problems??   The PTO
> unit is 42kc low on the low end and 53kc low in the high end.....  Is there
> a fix??   Also,when measuring the crystal activity with a vtvm thru a 1 meg
> resistor on pin 2 of V2,there is a significant change in the dc readings..
> The 10 meter crystal shows less than -1/2 volt,the 11 meter crystal -1 volt
> and the other crystals range -2.5  volts or more..  Is this normal or should
> all the crystals show approximately the same negative volts??  (The manual
> shows -4 volts..)    One last thing,the 2nd tunable IF,3.455mc to
> 5.455mc,tunes but is is very broad tuning there is a nice peak on the
> capacitor end but on the inductor end the tuning is very broad..   Is this
> normal..  I hope these questions are not to dumb...   Joe W.
> By The Way,the receiver work wells with good sensitivity,good volume and
> good selectivity...
> Just thought it might work better with higher crystal activity??
>
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