[ARC5] BC-230 / BC-430 coil set mod for 80m

[AKLDGUY .]

It appears there's a shortage of the 3200-4000 Kc/s coil sets, and to get
onto
80m most owners of the BC-230 / BC-430 will be forced to modify the more
common 2500-3200 Kc/s coil set.

The method suggested in another thread for modifying the ARC-5 6-9.1 MHz
receiver for 10m may be of significance for that purpose.

The methods suggested here do not involve removal of turns from the coils
or removal of capacitor plates.

Method 1.
If the wires labelled "bare" on the circuit diagram that go to the
oscillator and
final tuning capacitor stators are cut at the coil end and a capacitor is
inserted
at each cut, the frequency will rise. The values of the two
capacitors would be
determined by experiment, but once done by someone they will probably apply
in the case of every user.

That modifies the radio itself and would destroy the calibration chart
for every
other coil set used by that operator. If we go up from 2500-3200 to
something
like 3300-4000, each of the other bands will rise too. That might not be a
problem for some operators, since there is no direct frequency readout
anyway
and all settings are interpolations of the charts. The operator would
recalibrate
his charts for each of the other bands. Some may even want to take advantage
of this method to raise all other bands deliberately in one swoop.

Method 2.
A better way is probably to modify only the 2500-3200 coil set by cutting
the
same wires as above, but *inside* the coil set and fitting the series
capacitors
inside the coil compartments themselves. Cut the ends of the coils where
they
connect to their tags and insert the capacitors at the cuts. I'm referring
specifically to the hot end of winding "a" in each case, oscillator and
final.

No matter which way done, there is no DC voltage across either capacitor.
The capacitor for the oscillator could be a physically small unit, and fit
inside
the can easily. The capacitor for the final will need a higher voltage
rating due
to presence of more RF, especially when working into antennas of uncertain
characteristics.

I've looked at my C-381 coil set (2500-3200 Kc/s) and for the final coil
the tag
is exceedingly easy to get at and there seems to be enough room for a high
voltage ceramic capacitor of quite large size. The tag is the one connected
to
the soldered tap on the coil, not the roller tap.

These capacitors should be of very good quality, and after soldering must be
left to cool before testing, especially in the case of the oscillator.
I don't have a working BC-230 yet, so can't test the method.

73 de Neil ZL1ANM