Homebrew AM transmitter

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w3jn:
 ??? ???

I certainly didn't mean to come off as "colorful" or "unsupportive"; from the details you provided it appeared that you were re-inventing the wheel.  Nothing wrong with that at all, but probably not something one would want to tackle for a first xmitter project.

Far from my comments being "uncalled for", you asked for advice, I gave it.  Might I suggest you be a little more thick-skinned?  And I have a SB-400 that I've modified for hifi AM so your comment there is WAY off the mark.

If you're gonna do plate modulation there's no reason to build a heterdyne rig.  Build up a VFO for 160 or 75, multiplier stages as necessary, and run the final class C.  This is a LOT less complicated than trying to build mixers, getting rid of the image, etc.  Doublers are MUCH easier.  And building a VFO can be lots of fun  ;D

k4kyv:
The heterodyne vfo is more stable, because it runs all the time.  I have tried building one  a couple of times, but there always were some image frequencies strong enough to transmit a detectable signal outside the operating frequency.

My final approach was to use a conventional VFO, and just let it run all the time.  I used enough filtering of power supply leads and shielding of the oscillator unit to make it inaudible in my receiver.  Instead of homebrewing a vfo from scratch, I modified a T-368 master oscillator/buffer-multiplier unit.  It now  has  link coupled output, and I replaced the type 6000 tube with a 6AG7, and reduced the plate voltages to make the whole thing run cooler and thus drift less.  It puts out about 200mw on 160 thru 20.

I think the old Heathkit rigs run cw as well as slopbucket.  Maybe you could put it in the cw mode, and reduce the carrier output enough to allow 100% duty cycle, and use that to drive the plate modulated transmitter.  A lot of  hams do exactly that, using a ricebox.

The main trouble with those old SB and HW series Heathkits is the use of vacuum tubes on  circuit boards.  The same with the old Yaesu FTDX rigs.  They will inevitable develop intermittents, because of the heating/cooling  cycle of the tubes.  Tiny cracks develop in circuit board traces and solder connections around the tube sockets become intermittent.

w5rkl:
First, if I may say, I never meant to cause any problems or appear to. If it seemed that way, I do appologize.

It appears that my idea is similiar to what you tried, Don. My question is:

Ok, for the sake of discussion, my thoughts are to use a 3 meg and 12 meg crystal to produce
an 8 meg signal. Push that through an 8 meg resonate transformer, just like the one used in
the 400/401 sideband transmitters, and mix the 8 meg signal with the 5 meg VFO, using
a resonate tuned circuit on the second mixer's plate, producing an 80 meter signal. The 12
meg crystal, naturally would be different for say 40 or 20.

If the sideband transmitters can do it with very low images, maybe I'm not seeing everything here, why can't a
AM transmitter do the same thing without all the crystal filters, balance modulators and a much
better audio section? Just a thought.



73's

Mike
W5RKL

WU2D:
Mike,

An Apache with a heterodyne VFO and crystal bandswitching like the Marauder had would be quite a rig. Each band would tune with the same bandspread and the stability would be excellent. Best of all - no frequency roller, just a big sliderule dial.

I dub it the Mauraucny

I would keep everything else including the iron similar to the basic lineup of the Apache (or a modified Apache).

You should get the same 50 - 70 Watts out.

Mike WU2D

kc2ifr:
Sounds like Mike wants to start from "scratch". Whats wrong with that?????
I think the way u folks responded kinda insulted his intelligence......sorta like we are always right and u are wrong.
And Mike......jeese...who pissed in your Cheerios.....
One thing about the AMers..........very opinionated.....  ::)

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