[R-390] Z503, AGC amplifier anode coil

[Graham Baxter]

Hi All

I just had to rewind Z503 on my current project, EAC SN 162.

I was able to pick the coil and former out from above after
desoldering the top paxolin plate. The glue used for assembly will
soften and crumble with the heat from a soldering iron.

The ferrite cup was fixed to the coil using the same glue. By running
the iron around the top edge and gradually pulling and rocking the
former it all pulled out without breaking the ferrite. It got too hot
to hold with the bare hand though. The cup needed some patient
scraping to remove all the glue debris.

The middle pie of the three had rotted and turned green. This
explained the 700 ohm resistance instead of 17.

In case anyone is interested I can confirm that Z503 has three
identical pies, each wave wound with 120 turns of litz. The litz has 5
strands of 0.002" (0.05mm) enamelled wire.

Since I was disinclined to use a wave winder ( I do have one in the
loft, but I have never understood how to use it!), I random wound it
using rubber washers as spacers. The washers were lightly oiled before
winding. As each pie was completed I soaked it in superglue to make it
self supporting. On completion I removed the washers by melting a
small hole through the edge of each one and picking them out with
tweezers.

I consider myself fortunate that my new coil will peak up with the
original 82 pF capacitor; I was quite prepared to select a new value
if necessary.

Graham Baxter
G8OAD