heating and such).
If the "no-load/load" voltage difference is negligible (<0.1 VDC), try
adding a filter capacitor (start with a
470 µF electrolytic — watch the voltage rating of the cap!) paralleled with
a 0.01 µF mica or polyester to filter out
high-frequency hash that may be on
the DC output feeding the clock. This
may give you the stability you're looking for as most — if not all — warts are
half-wave unregulated types with very
minimal filtering to begin with. Adding
more filtering (larger electrolytic) and
bypass (small value) caps to the DC
output greatly improves their overall
stability and cleanliness of the DC output voltage.
Finally (as you already know), having a regulator between the wart and
your device guarantees a rock solid
DC source, as long as you don't pull
too much current from the wart.
[#2153 - February 2015]
Can you PLEASE indicate which
germanium diode would best fit this
SW radio? Either a 1N34A or 1N60?
#1 Both diodes — 1N34 and 1N60
— are germanium diodes, and both are
of similar physical size. The important
thing is that this diode family has the
smallest forward voltage characteristic,
which is important for rectification of
small voltages. They both will operate
at radio frequencies. The forward current rating and the reverse voltage
characteristics are unimportant in this
Bottom line: Either one will work
in this application. My personal choice
would be the 1N60 because the documentation available for this device is
superior, with V-I curves to show the
typical forward voltage characteristic.
Peter A. Goodwin
#2 Either should work well. Both
have a conduction knee starting
around 0.15 or 0.20 volts. The
IN60 — being slightly newer — probably has more tightly-controlled specs.
Here’s a source for diodes and their
conductor.com/1n34a.html. BT W, for
better Q of the tuner, connect the
diode to a tap on the coil.
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March 2015 79