[Collins] Identifying BBs

[Dr. Gerald N. Johnson, electrical engineer]

I've tested many molded paper capacitors in the past 30 years, though I
quit testing them 15 or 20 years ago. Only a few passed my leakage test,
while Sprague Orange Drops have passed my leakage tests very well even
after a pass through the ringer washer and dryer in my pants packet 40
years ago or so. The modern Orange Drops are made quite well and should
do as well. 

The only mica capacitors available today are dipped silver micas. They
are decent replacements for molded micas of old, generally with better
stability, though rarely some come faulty.

Polyester capacitors like Orange Drops do contribute far less noise and
bias shift for the audio stages.

Metal film resistors may have lower noise, but the noise from high value
resistors isn't a great factor if the receiver gain distribution is
proper.

There are other makes of polyester capacitors, some may be as fine as
the Orange Drops, but I've had more experience with Orange Drops and
they have been very consistent over the past 40 years.

Carbon composition resistors will have changed values since the A4 was
built. They started changing when they were soldered into the circuit
and the combination of heat and humidity cycling has continued the
change. Leaky screen bypass capacitors also tend to cook the screen
dropping resistors.

Metal or carbon film resistors are workable replacements for carbon
composition resistors in most applications. Watch the power dissipation
rating and the voltage rating. The film resistors have some added
inductance from the spiral cut of the cylindrical film to raise the
resistance, but at HF I've not found the Q of the inductor to be a
factor in circuit operation. The resistance swamps the inductance so
inductance isn't a significant factor in circuit operation.

For appearance, carbon composition resistors would look better, but film
resistors will work just fine and are easier to find.

Orange drops do change the appearance form the black beauties, but are
very good capacitors that won't have to be replaced again.

A few values of carbon composition resistors are available from Mouser
Electronics (www.mouser.com) and they carry a full selection of Orange
Drops at decent prices.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.