Hi David,
> the plate bypass capacitor is a 0.1 uF paper capacitor.
Plate BYPASS capacitor? Is that circuit a cathode follower? Otherwise
there shouldn't be a plate bypass capacitor! Perhaps you mean a plate
COUPLING capacitor?
> There is also a 0.1 uF
> paper capacitor as a cathode bypass on the pair of PL-500's. Is there
> any reason why I shouldn't replace these with 0.001 or 0.01 ceramic
> disks?
Most certainly yes. A 0.1uF capacitor has a reactance of one half ohm at
80 meters. A 0.001uF cap has 50 ohms. When the cathode impedance is just
a few tens of ohms, which is probably the case with those PL-500's, a
0.1uF is a good bypass, while 0.001uF isn't a bypass at all!
If the plate cap you mean is a coupling cap, then a much smaller value
might work fine there, because the plate impedance is pretty high. But
not at the cathode!
The main technical reason to use a 0.1uF cap as plate coupling cap,
might be to achieve low frequency stability. Although not so common with
tubes as with transistors, leaving the device unterminated on a low
frequency can easily lead to self-oscillations. So, while the 0.001uF
cap will surely work well enough coupling RF, it might make the PL-500s
self-oscillate at audio, depending on the rest of the circuit!! But it's
not very likely.
Anyway, if you are RESTORING the radio, try to keep as close to the
original design as possible, even if just for the sake of authenticity!
There are some high quality 0.1uF 1000V polypropylene caps out there,
which even look good in old equipment!
Manfred.
========================
Visit my hobby homepage!
http://ludens.cl
========================
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|