The very early HRO's were aligned with the coils that were shipped with it
and also serialized to the receiver. Finding a matched set is very hard and
commands big bucks. Ive enough to do on my 2nd run March 1935 version
without worrying about matched coils (yet).
We got plenty of all era HRO's in for service and a jig was not used. Once
you got the knack it was easy. The holes in the chassis are there for a
reason.
Carl
KM1H
----- Original Message -----
From: "D. Chester" <[EMAIL PROTECTED]>
To: <amradio@mailman.qth.net>
Sent: Tuesday, November 27, 2007 1:56 PM
Subject: [AMRadio] HRO-50
My pre-WW2 HRO's have a hole in the chassis just behind the panel and
next to the main tuning capacator. You can access the trimmer caps with
the coils plugged in. I'm pretty sure the later models also have this
trimmer access. I use a long 1/4" nutdriver. It doesn't seem to detune
the coils, but be careful. Some of those adjusting screws carry the full
B+. I have been knocked on my bum while aligning HRO's.
The low-end adjustment requires opening up the coil to move a one-turn
loop of wire, which changes the inductance of the coil.
The only way I could think to make this adjustment other than what you
mentioned, would be to build up a jig where you could mount the coil with
the cover removed and gain access to the coil, while it is connected to an
oscillator tube or an rf amplier tube with an external signal generator
and output meter, to indicate when the rf coil or oscillator coil is
properly aligned. Even that would be approximate, because the adjustment
may be off a little when the coil is re-mounted into the shield and the
whole assembly is inserted into the receiver. For the alignmentt jig,
perhaps a spare shield could be modified by cutting open the end to allow
access to the coil with at least most of the shielding in place.
This would be a good project for National affectionados who regularly do a
lot of HRO alignment.
Don k4kyv
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