my own variation of the triode/pentode family of glowbug transmitters.
It features a Pierce oscillator which runs continously during
transmit to avoid chirp. The PA is grid block keyed and since
the negative is there, fixed bias. The bias setting is not critical,
grid rectification will provide additional bias and form a sort
of regulation network. The PA is biased into class C,
adjust bias for about -24V at keydown, measured at the junction
of the 3 resistors. Plate current should be around 35-40 mA when
fully loaded, depending on crystal activity. Power output is 5
to 8W at 12W input which is a healty
66% efficiency (not counting the screen current) and a nice blue
glow comes from the innards following the keying. My original
plan was to use a Pi-L tank to meet the modern demand of spectral
purity but with loaded Q higher than normal, not really needed
in this power class. The idea with grid blocking was to enable
me to use my keyer without any relay in between. It has a negative
keying line with a 250V filledstate device behind.
When tuning up, mesh the loading condenser C2 fully
and dip the plate with the tuning condenser C1, quickly! Plate
current should dip down to around 20 mA. Unmesh tle loading condenser
C2 until the current just stops rising or maximum 40 mA. Redip
the plate. Repeat until the dip is shallow, a few mA. Do not tune
for maximum output, the PA is not neutralized and will run beyond
maximum tube ratings if this is done. If maximum output goes over
9W or loaded plate current over 40 mA, lower the plate supply
or back off the grid condenser a little or mesh the loading condenser
a little. The plate current should not exceed 40 mA fully loaded
(ah, well, the tube is still available from Russia :^),
maximum allowed cathode current is 50 mA for this tube. I have
installed a 100 mA meter in the wire going to the plate of the
PA. The glowbug is free from chirp and runs smooth. Keyline filtering
seems to be unnecessary but check the envelope if you are driving
a power amplifier with it. I have found that the grid condenser
could be replaced with a 47 pF fixed for FT243 rocks and 15-22
pF for modern tin can rocks.
switch? I use a rotating switch
with 3 poles, one for switching the antenna, one for+300V on/off
and one for the receiver mute. If you use a regenerative tube
receiver, antenna switching isn't really necessary, use a separate
short wire as RX antenna or couple lightly to the TX tank. The
regen grid leak and coupling condenser should be adjusted for
proper recovery between the code elements (full QSK)
or perhaps between words.
Only a simple rocker for the +300V is needed.
Spotting? Well, my Heath SB301 gives this away for free. Set the RX in receive
mode and engage the T/R switch without keying. You will hear the
triode oscillating in the receiver. Tune it in and reset the RX
in standby mode again. Advantage, gridblock!
Sidetone? Many ideas here. I use my new keyer's sidetone. My previous keyer did
not have sidetone, instead I used my
TS-830 as a growler, he, he... Or use a small 50 mA lamp in series
with the PA plate as a sidelight :-), at least at QRS speeds.
Circuit layout? Not very critical. Only one tuned element except the rock is present.
As a starter, keep the triode circuit on one side of the tube
socket and the PA section on the other. Use the middle stud on
the tube socket as a common grounding point if there is one. Keep
the rock at least 2 inches away from the tube envelope to avoid
heating it. The schematic does not show the heater, ground one
side and decouple the other side at the socket with a 0.01 ceramic
condenser. Heater voltage is 6.3V. If it exceeds 6.6V when loaded
by the tube, add series resistance until below for maximum tube
life. My own is built in a aluminum cast
box with all circuitry inside it except L1, C2 and the output
choke. If you use loads other than 50 ohms, some fiddlin' with
the tank may be called for. You can also replace the pi tank with
a link coupled parallel tank. For data and pinout on the tube,
tube data (http://www.algonet.se/~janax/secl82.htm
Running rock bound?
Not easy. You call CQ. Don't wait on the rock QRG for others unless others
knows about you. Sometimes you hear another
station calling CQ near your rock QRG. Give him a try, he may
hear you. It might be easier to use the QRP QRG 3560 kHz. In US,
3579 kHz is a common rock QRG. Use a 3579R545 kHz color burstie
rubbed down a tad. In EU at night, most glowbugs seem to stay
around 3560-3565 kHz.