On Jun 11, 12:50*pm, "Alex Pogossov" wrote:
"flipper" wrote in message
...
Okay, so I like to make up cutesy names 
I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.
This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).
The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.
Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.
http://flipperhome.dyndns.org/Beamus.htm
But the smartest arses (aussies of course, he-he!) put their AM transmitters
in the vintage radio cabinets.http://www.ebay.com.au/itm/140770446...ELX:IT&_tr...- Hide quoted text -
- Show quoted text -
Hmm, I must qualify as a dumb-ass aussie because I've not tried to
make an AM transmitter in such a nice package, all kinda trick stuff.
But you know, I recall that while I studied FM tube radios so I could
service them properly in 1995, I mentioned production of an FM test
signal by means of a reactance tube FM modulator to a bunch of radio
enthusiasts at a ham gathering one evening to see if they had any
schematics or knowhow. None did, and one said "Mate, waddia wanna vary
frequency for? We jus wanna keep the frequency stable, eh..." Well,
OK, they were stuck back in 1955, most were over 70 in 1995. Now most
are dead, and I'm still lingering with audio F stuff, having
farnarkled muchly with RF home brew testorator checker thingies.
But I was about 15 when I made my own transmitter out of an existing
old radio set. I got my sister to talk into the crystal mike while
walked up the street to see how far it broadcast, using my mum's new
Japanese 9 transistor portable. After I'd gone about 1/4 mile dear
sister starts saying "This is the illegal broadcast by Patrick Turner
from No ----- street....." and then I qualified for the Olympics 400M
getting back home to shut the sister up. Females can be cheeky, and
sis was no exception.
I have an idea to make another modulator which might work merely by
having 3 cascaded variable µ pentodes, each contributing about 30% AM.
maybe it works, maybe it don't, but it'll have to wait until so many
other things more worthwhile are completed.
In Canberra we get ABC Radio National on 845kHz AM with AF BW allowed
to be 9kHz, so my AM radio has 10kHz BW using variable selectivity in
the 1st IFT by varying the distance between the coils. But one could
always use the Internet to get the podcasts at
http://www.abc.net.au/radionational/podcasts/program/
And you just subscribe. In many places RN is broadcast on FM, and now
in digital stations.
So I guess one could tune into RN on the digital and use the audio to
modulate a carrier for the AM radio to pick up, and that should sound
better than if one tries to pick up the local AM radio station pumping
out 5kW, and only 4km away.
Just don't ask me to describe how digital radio works. I looked for
radio schematics and found none, seems like secret business nobody
wants me to know, but seems like the digital band is at UHF or around
250MHz, and just what the wave forms look like I don't know.
Patrick Turner.