[Boatanchors] Fw: HRO coil alignment.

[WA5CAB at cs.com]

Al, et al, 

No one else has piped up so I'll throw in my two farthings worth.  I've never 
worked on an HRO and haven't laid hands on one since the early 60's at LSU.  
But if the manual says that's how you have to track the lower end, that's how 
you have to track the lower end.  The BC-312 family are the same way, and much 
more difficult to get to.  I once spent days retracking the HFO in a BC-344.  
Fortunately the Antenna and RF boxes were OK.

As far as whether you want to go to the trouble or not, if it's your receiver 
it depends upon how close to bang on you want it versus how much time you are 
willing to spend at it.  If it belongs to someone else, it depends upon how 
close they want it versus how much they are willing to spend.

I recently finished a partial restoration of a BC-312-M for a guy who mainly 
wanted it working and not likely to burst into flames in his law office.  It 
had been his first ham receiver, then someone else apparently was going to 
improve it for him and did a real butcher job.  Anyway, it needed to work reliably 
and not be deaf but if WWV showed up at 15.2 MC on the dial, that was no 
biggie.  So after I took care of the fire hazard and other major butchery, some 
leaky caps and crispy critter resistors, I aligned it on each band at the book 
points using only the trimmer capacitors.  And then checked the results at the 
bottom of each band.  All were low output compared to the top, and off 
frequency by a bit.  I then went back and set the oscillator at about the 75% point 
up from the bottom of each band and checked just the oscillator tracking.  In 
retrospect, I probably should have used the book set points on the dial and 
just offset the oscillator by some figure, maybe 1/3 the error at the bottom for 
a starting point.  But I only thought of that later.

Then I tweaked up the Antenna, RF's and Detector trimmers at the top, set the 
signal generator to produce a known audio output voltage (using a dummy load 
audio output meter) and went to the bottom of one band and noted the output 
voltage.  It was low.  I adjusted each of the four trimmers one at a time to see 
which made the most difference, setting the output back to the noted reading 
after each tweak.  The two trimmers that made the least difference I left 
alone.  The two that made the most difference I adjusted to bring the output up to 
in the end about 2/3 of the tweaked high end voltage.  In the end, the 
frequency calibration wasn't off too badly anywhere and the sensitivity was good 
enough across all of the bands (even surprisingly enough the top band) to pull in 
Radio Havana anywhere I knew to find it with no more than a meter test lead 
for an antenna.

If it had been my set at the point at which I finally started the alignment, 
I probably would have opened up the coil boxes.  But on the other hand, if it 
had been mine and in the condition as when I first saw it, it would have been 
designated as a parts set to begin with.  :-)

In a message dated 10/7/2005 6:26:33 PM Central Daylight Time, 
anchor at ec.rr.com writes: 
> Yes, please answer to the list, I have an HRO-7 with similar needs.  I've
> talked with Olaf b4 about it, we both need advice.
> tnx, 73,
> Al, W8UT

Robert Downs - Houston
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