[ARC5] 70+ year old errors found and corrected.

[Kenneth G. Gordon]

You know that 1.5 - 3.0 MHz coil box I was having troubles with? The one out of the receiver 
that had been hacked for crystal control back in the 1970s?

Well, today, not having anything much else to do (yeah, right), I decided to take a closer look 
at it to see if I could figure out exactly what was wrong with it.

First, since the HFO coil had been the one that had been messed with (I figured this out 
when I looked at the screws holding the coil in the box: there were 2 different kinds, and the 
paint had been "broken").

Although I had restored the two resistors, R-3 and R-6 to their original values, the HFO still 
didn't work. I looked more closely at the connections to the coils and after taking my glasses 
off and looking VERY closely, I discovered that one lead of the plate coil was no longer 
soldered to its connection. What looked at first like solder was flux, and all 6 of the Litz wires 
were not soldered. When I had tested the coils for continuity, I had clip-leaded one lead of the 
ohm-meter to one end of the coil, and had used the probe on the other end. The clip-leaded 
end turned out to be the open one....of course.

Have any of you 70+ year old folks ever attempted to 1) clean the enamel off of 6 pieces of 
#60 Litz wire, and then 2) solder them in place with shaky hands? Well, I managed...finally.

Putting it all back together and installing in my working receiver, I found that the HFO was 
now working, but the signal through the mixer was way down. However, the RF amp did peak 
by the Align Input control, so that meant that the RF amp coil was OK.

Back to the coil box. After swapping the good coils, one at a time from my working coil box 
into the non-working coil box, I zeroed in on the mixer coil as the culprit. Obviously, however, 
the coil had never been tampered with as the screws still had their red paint on them and 
they were very tight.

Even so, I removed them with some effort, and removed the coil. Using my clip-lead and 
ohm-meter I again determined that both coils had continuity. Furthermore, there were drops 
of the original ruby-red enamel on all the connections.

Then, remembering my experience with the HFO coil, I used both of the ohm-meter probes, 
without any clip-lead, to check continuity through the connections at the bottom of the coil 
from outside it.

Sure enough: one coil no longer had continuity.

Again removing my glasses, I looked VERY closely at the two connections of the now open 
coil, both of which looked "factory" and both of which had that ruby-red enamel on them.

One of those connections had never been soldered: the Litz wire had been wrapped around 
the connection, never soldered, and then had been covered with ruby-red quality-control 
enamel. 

A 70+ year old construction error, followed by a quality-control error uncovered.

A few seconds with the soldering iron and solder fixed the problem.

Re-installing the now repaired coil box proved that the receiver was now working properly.

Alignment followed, and I am now listening to it.

Sheesh!

Ken W7EKB