Gents,
I know yal are dying to know about my project to resurrect my old amplifier
so I can use it in SS this weekend using my K-3 for input.
The bad news is that some of my test equipment, like my VF/HF grid dip
meter and my old Heathkit Q meter failed to work. The good news is it hasn't
mattered so far. With the K-3 set to produce 3 watts and using it in the tune
mode one can see the SWR in real time right on the front panel display. Also,
I already had a flexible coax cable with a PL-259 for connection to the K-3 RF
output and a pair of alligator clips at the other end. I also had a
three-section,vintage-radio variable capacitor wired in paralled for use in
finding resonance with any unknown HB coil. No matter what the inductance in
mHy, this capacitor is likely to resonate on some ham band transmitted by the
K3, now used only as a signal generator/SWR bridge combination (I love my K3).
I have many non-inductive 2-watt resistors from my years repairing TV sets as a
night/weekend occupation, so I had the requisite 90 ohm resistor to be
subsituted for the 4-1000A. All I needed to do was to copy the con
struction of similar amplifiers to model my needed set of inductors and as far
as diameter of the slug-tuned coil forms and turns of wire required was
concerned. I could use the enameled wire from the coils that I took from my
old amplifier since it was tuned (but not matched for low SWR) before.
It was a 12-hour day yesterday day to get the 160 meter tuning finished and
installed on the rotary 3-section, 18-position switch used in my original
amplifier. Yes, it has 18 positions, but I often use three adjacent positions
of terminal lugs on the switch for both space and mechanical rigidity. I use
all three sections, one for the band-coil's bottom end. one for the same coil's
tap, and the remaining one for the top end of it. Two of every adjacent three
switch positions are unused electically, but provide the space needed for the
parallel capacitors and solder points for them. All of the bandswitch's wiring
is taken from a foot-long B&W "miniductor" from my junk box. It solders easily
because its silver plated. I label only the six active positons on the front
panel using trimmed-down Avery labels.
First band done: 160 meters. This band required a long, 14-hour day
because of the need to first test the test equipment, and then derive a
practical approach. Also, I had no idea that the triple-section capacitor
wouldn't tune this coil to resonance. Fully frustrated, I actually had to put
a 2000 pF mica capacitor in parallel with it in order to achieve parallel
resonance. Before this I was seeing double-digit SWR's on the front panel of
my K3 (which might have damaged it if it hadn't first set it for only 2 watts
of RF output). Since the plate resistance of a 4-1000A is relatively high, one
connects the K-3 signal source to the coil tap and a 90-ohm non-inductive
resistor to the coil's top (the bottom is grounded for both since my
amplifier's bias applied using the filament route, not to the grid (through
the filament 's RF choke and associated transformer's secondary center-tap.
I was able to take the time to bring you guys along on this construction
adventure leading to my participation in SS starting tomorrow because I doing
well with it now. I have not only finished installing the 160 m
resonator-match tuning, but also that for 80 meters. So far I've achieved an
SWR of less than 2 to 1 with either band using my test setup. Also its going
to be easier from here on without having to extensive searches through the junk
box to find the capacitor that matches my requirements. I have an
already-sorted set of boxed micas values of less than 550 pf.
For maximum score in SS I should use a horizontal antenna instead of my
low-angle vertical GP, and I'll have to find another coax for it since it got
run over while I was mulching leaves, but I still think that I can make it if
I'd stop what I doing right now. Lol.
Anyway, since I'm still a homebrewer in a sea of "modern appliance
operators" as they say, I thought you guys might want to travel along with me
on my path towards the SS contest this year. In my opinion, by the way, is
that HBing is only a bad job before you've discovered exactly what to do. Its
faster, and easier, after that.
Respectfully,
John, W8OHT (WN8OHT in 1953)
P.S. Gotta go now! thanks to those who spent time answering my question about
tuning/matching amps in the two most recent amps/contesting essays.
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