Description
This article is from the Antique Radios
And Phonographs FAQ, by Hank van Cleef vancleef@netcom with
numerous contributions by others.
45 Philco cathedral radio - Can I get it to work better than it does now?
I have a nice old Philco cathedral radio that I have listened to for
years. It only gets local stations, and even at maximum volume, is not
particularly loud. Can I get it to work better than it does now?
Probably. You have a sixty-year-old piece of electronic equipment
that has probably had two or three tubes replaced, and maybe one bad
capacitor, in those sixty years. In short, it's a candidate for an
electronic overhaul. Some things that may have degraded over the years:
a. Capacitors. Electrolytic capacitor problems generally make
themselves known quite quickly. However, those little wax-impregnated
"paper condensors" may all be leaking current and delivering less
capacitance than needed for good performance.
b. Resistors. These may have "drifted" to a much higher
resistance gradually.
c. Misalignment of tuned circuits. The "tweaks" on the tuning
condenser and the IF transformers generally don't drift very far unless
the coils have absorbed moisture. Altogether too often, the amateur
restorer will tweak the set out of alignment by fiddling with these.
Don't touch them unless you know exactly what you are doing and have the
equipment needed to align the radio.
d. Tired tubes. I put this last, although a lot of people look
here first, and assume that a tube tester's readings will correlate with
set performance. The best test for tube condition is to substitute a
known good tube in each position and seeing if it changes anything. A
sick pentagrid converter tube (6A7, 6A8, 6K8, 6SA7, etc.) may very well
test normally under DC conditions in a tube tester yet fail to oscillate
reliably in the set, particularly on shortwave.
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