Modulation impact when amplifying a DSB signal?

kd4e doc at KD4E.COM
Mon Feb 16 14:12:57 EST 2009

Just found this neat discussion:

Look as though it will run on 140v, perhaps as low as 125v - not sure
if the tube characteristics mandate the 140v?

Hmmmmmm ...

>  Well, that's interesting.  Why the low voltage?  Batteries??  All
>  these circuits will work better at higher voltage.  5W input is 40mA
>  and 5W output will take twice that, I expect.  If you are talking
>  PEP, then much more. That's a lot for the small tubes.
>  The high level balanced modulator is the way to go for DSB, avoiding
>  the amplifier problem.  I remember the 7360 tube which was made for
>  this, but don't think it went to 5W...look it up.  There used to be
>  lots of 7360 circuits in the Handbook and QST.  With the full QST
>  archive on the ARRL website, reference work has been facilitated
>  dramatically!  If filament power is not a big problem, any two RF
>  tubes would do.  6AQ5s are cheaper than dirt and would do it easily.
>  Going farther back, a pair of 6AG7s would be great, in octal sockets.
>  I have circuitry froom the 30s doing it with a pair of 6V6s,
>  probably fine at least to 40 meters. You could keep the filaments of
>  the TX off most of the time, just turning on during contacts.
>  To go fully retro, you could find an old Vibrapack for the HV, or
>  build your own.  Vibrators are available at many hamfests and on many
>  websites.  Who knows, you might get to 10W, which would be a pretty
>  useful SSB signal!
>  But I'd encourage you to bite the bullet and go SSB, maybe learn some
>  circuitry along the way.  When I was in grad school, I built a 50KHz
>  acoustic command link for use in the sea.  It was SSB, phasing
>  method, and worked great.  I could go thousands of feet in water,
>  never got to max range, and it worked fine as RF around the lab.  I
>  tested it by running an FM radio through it and casual listeners
>  coming by the lab didn't notice I wasn't listening to the usual
>  radio.
>  The phasing was done with the Dome network, as used by B&W in their
>  commercial product.  I simply copied their circuit and used opamps
>  instead of tubes.  My carrier phase shift was done with two ten cent
>  transistors and simple RC lead/lag elements.  I could give you the
>  schematics for all this. I may even have a set of the RC components
>  for the network.  The idea of produciing a nice SSB signal with a
>  couple of 9V batteries is pretty appealing!  So is the idea of a
>  whole rig running on a little gel cell or plugging into any car
>  dashboard!  I'm about to embark on a qrp project myself, but probably
>  CW only for now...backpacking.
>  Please tell us more about your objectives.
>  73, Wilson W4BOH


Thanks! & 73, doc, KD4E
Free OS :
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