Those and pentodes (such as 1T4) work fine as mixers on
up to 10m in consumer radio receivers such as the Zenith
Transoceanic series...but they are starting to get rare, as
are 7-pin miniature tube sockets using ceramic or mica-
filled plastic dielectric!
Yes indeed, the 1L5 and 1T5 are getting extremely costly.
I had been doing other surfing between our exchanges. I found a
duo-triode battery tube, one of those could make a long-tailed pair
mixer. I also found a duo-diode plus pentode, and a diode plus
pentode. Two of the former tubes could make a 4-diode mixer plus
signal/buffer amps on each side. Two of the latter tubes could make a
2-diode mixer pls plus signal/buffer amps on each side.
Okay, then drop the "EMP withstanding" personal specification.
Common sense says: Individual stage shielding and bypassing
anything that isn't an RF/AC signal; have the power switch also
short the antenna input; put in back-to-back switching diodes on all
RF/AC stage-stage lines that aren't handling more than a 0.5 volt if
you must have some kind of EMP withstanding capability.
"EMP" is ElectroMagnetic and is a very broadband impulse. It isn't
juju or magic, just very high level Ultra Wideband stuff. It doesn't
reach in to find out if a circuit has tubes or transistors, selectively
blowing out only the solid-state things. Approach the total design
with this super UWB environment, looking at EVERYTHING that
might pick up the super UWB of an EMP. If you want real
survivability, then get a sturdy metal box with an excellent
conductive seal all around and store the radio in there. Add a sign
telling others what is there since local humans can be fried by an
EMP through their own internal wiring.
All very good suggestions, thank you. So if EMP is simply a noise
spike from DC to daylight, is it that I should employ traps on all
input and output leads to shunt everything outside the band of
interest to ground? And the metal box makes sense.
Or, just have fun making whatever you want to make, hoping the
powers-in-charge never decide to use an EMP beastie.
Um yeah, like I said, this design is for my daughter and her cousins
for thier 10th-12th birthdays, with another for myself, so I have at
least 7 more years
to get this working.
So how's this for a possible lineup for the receiver?
Preselector: grounded grid amplifier with variable tanks on each
side.
VFO: triode oscillator with low voltage neon bulb as
regulator and
variable tank.
All three tanks use a single section each of a 3 section variable
capacitor.
Converter: duo-triode differential amplifier as mixer.
IF filter: Crystal lattice filter, 8 Mhz IF, 3-6 khz bandwidth
Detector: single-tube regenerative detector fixed to 8 Mhz with +-
6 Khz
tuning through a small variable capacitor added to the
capacitor
in the 8 Mhz fixed tank. Also has a manual regeneration
control.
Audio amp: standard OTL implemented with battery tubes.
Output to 1 Watt speaker.
In theory, the IF filter with the 3-6 Khz bandwidth provides me with a
window open either to SSB or CW. The fixed detector would allow me to
receive either SSB or CW depending on the setting of the regeneration
control. The detector would be 'tweakable' +- 6 Khz to provide some
degree of passband tuning against the IF window.
Now the transmitter:
I have a novel idea for the CW transmitter to reduce the size of the
final amplifier tube and the heat dissipation. Implement the final
as a high frequency pentode or beam tetrode wired in triode mode,
running as class E. I could possibly take that type of battery tube
meant for 200 mw IF amplification, and run it at 5 watts class E
without much great harm to the tube.
Anything I am missing with this lineup?
The Eternal Squire