[Boatanchors] Fw: HRO coil alignment.

[Alan Cohen]

Although I am not an expert, I am rather fond of HRO's.  I've  
restored a few of them and they perform very well for a design that  
dates back to the mid 1930's.  One of the things that I like about  
them is that they are very easy to fully recap, and have no  
complicated band switches.

What makes aligning an HRO a little bit different from other  
receivers is that the coil sets have a bandspread and a standard  
setting.  Depending on the vintage of HRO, you move a screw or a  
lever on each coil to change the setting.  The factory alignment  
procedure calls for first setting up the standard tuning and with  
that accomplished setting the bandspread.

My major interest was using the receiver on the ham bands.  Because  
of that, I didn't work too hard getting the standard setting to track  
perfectly.  It's been a few years since I did an alignment, but here  
is what I have to offer.

We are very fortunate to have test equipment that was not available  
when HRO's were in production. For each coil set I calculated the  
injection frequency for each end of the ham band.  Next, I used a  
scope probe hooked up to a frequency counter to couple a little bit  
of LO energy into the counter.  With a little bit of experimentation  
I found a place where I could couple the counter without loading the  
LO to the point that it shifted frequency.  I changed settings the  
hard way, plugging the coil set in an out each time I wanted to make  
an adjustment.

Once I had the LO tracking, I used a signal generator to get the  
other three sections to track.  It is very tedious, but not  
particularly difficult to do.  I hope that helps.

Good luck,

Alan




On Oct 7, 2005, at 11:16 PM, WA5CAB at cs.com wrote:

> 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
> <http://www.wa5cab.com> (Web Store)
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