[AMRadio] Re: How can we rid the HF bands of AM ?

Geoff w5omr at satx.rr.com
Wed Aug 10 23:08:20 EDT 2005

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 

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."

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,

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