Patrick Jankowiak wrote:
Hey Geoff,
You are right, I won't be totin' the Tucker KW or even the BTA-250..
For me the AM is a hobby and a love for doing things in one of the old
and respected ways. No General yet, maybe soon. I have alot of fun
just fiddling with them.
You like fiddlin', and that's fine. But, for me (and I think some
others here agree) there's nothing finer than saying "rig here is
homebrew" and getting that "man, that's a good sounding rig" report in
return. The feeling is indescribable.
The Transmitters/restorations are on hold as I am doing a major
clean-out of my lab. Each weekend we have been hauling 800 lbs of junk
to the landfill, it is -most- politically incorrect. nothing of
interest here, unless someone wants old 9-track computer tapes and
stuff like that.
You never know what someone will buy on ebay. At worst, it hangs around
your shop another week. At best, you have something that someone else
thinks is an antique relic and is 'just the part' they need to finish
out their collection. *shrug* hey, it could happen ;-)
I tried to sell a 450TH, appearing as if it was unused, no scratches on
the base - asked in here for $50 for it, in the metal spring-loaded
shipping frame, in a box. No one bit. Put it on ebay for 7 days, and
started it off at 9.95 and it sold for some 3X (plus shipping) what I
was asking for it originally, in here.
The worst than can happen is, it hangs out for a week.
For what was lost, well that is true to a degree and 3 or 6 dB does
not make that much difference at the other end, but I guess I am
looking at the old Tucker rig and knowing its audio and RF power
supplies are good for 3KW DC each. COL Tucker built it for military
communications from Dallas to Austin. I mean, the thing was/is capable
of who knows how much audio input on top of the KW DC. I'm thinking of
the peak power. It just seems a shame to idle it out along the
wireless in 2nd gear. The upside is that it will probably last forever.
Think of the money you'll save on spares ;-)
The status on that beast is that there is a parasitic oscillation in
the final's grid circuit, between the 4-1000 control and screen grids,
at about 140MHz. Plate tuning, current, and neuralization setting do
not matter or vary much at all with this issue and the grid current
and screen current interact alot. I found that a 50 ohm resistor in
series with the grid helped. Maybe I need to increase that value or I
don't know.. The screen grid is heavily bypassed directly at the G2
terminals on the socket, and an RF choke is optionally in series with
the screen to the chassis connector to no effect. This oscillation
happens no matter if the grid drive connector is shorted, open, or
terminated, so this tells me it is in the control grid circuit
somewhere. Nothing's been changed from the original design there, so
it is further mysterious.
Just for grins and giggles, try putting 2 50 ohm resistors in series to
ground, and then the grid to the center of the two 50 ohm resistors.
It's helped other rigs.
Also, I need to rig a 220V 30A outlet and power cord for it. I keep
popping the 120V breaker when running up the final and modulation
sides together (the unit has two 120V plugs presently).
Seperate 120v circuits?
As far as audio, I'm willing to help anyone who wants better quality
sound from their AM rig. I'm not a great RF expert at all but I am OK
with increasing the fidelity/reducing distortion in audio amps.
But.. one works hand in hand with the other. In fact, John/WA5BXO and I
have been discussing (at length, and credit to John for sticking with me
and my dumb questions ;-)) audio, it's effects on the transmitted
carrier, how much voltage is neeed to fully modulate the carrier and
what is needed in the way of a reactor to sucessfully couple the audio
to the B+ line to the final amplifier. This conversation encompassed
power supplies, through the modulator and the final. All components are
cruicial.
John and I also talk, from time to time, at length about asymetrical
audio. I've achieved it, somewhat.
Sometimes technology is overwhelming.
For less than $100, I bought not only a digital camera that takes
amazing 3.2megapixel pictures, but it also has a 'movie' mode.
No audio, but the movie mode is pretty awesome.
"Hel-l-l-l-l-o test. one, two, three, four."
http://w5omr.shacknet.nu:81/~w5omr/pictures/2005-08-08/000_0049.MOV
The 'noise' you see is a box-fan at full speed. It was over 100° here,
that day.
At this moment I'm limited to NVIS type antennas, but I have a tower
to put up. another project. I hope a tower will get me better
shortwave listening due to a higher antenna (and give me a place to
put a 6M beam for FM).
Mike/WA5CMI has been on 6m lately. He's in Garland, not too far from
you. Maybe y'all could hook up and check out 6m together.
he's probably monitoring either 50.4 or 50.125 - give a holler for him.
As for the general... that's a cinch - cup o'tea - piece of cake. Take
it. Get it over with. You'll feel better, and you can then put them
rigs on the air. ;-)
---
73 = Best Regards,
-Geoff/W5OMR
