Homebrew AM transmitter

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Good morning everyone,

For some time now I have always wanted to build a
homebrew transmitter. I have come up with a idea
that I think should work ok.

The idea is to reuse some of the old Heathkit SB/HW
transmitter/transceiver carrier and hetrodyne
oscillator crystals and the LMO/VFO and a few other components.

The SB/HW series transmitter/transceiver's CW carrier
generator crystal is 3.395.4Mhz and the 80 meter
hetrodyne oscillator is 12.395Mhz (for 80 meter
operation). There are other hetrodyne crystals that
can allow multi band operation possible but the info
I provided here are for one band only, if nothing
else, to get it operating first. The transmitter could
be changed to add multi band operation.

The basic circuit consists of the 3.395.4Mhz CW crystal
oscillator that is fed to the first mixer where it is
mixed with the VFO frequency of 5.500 to 5.000Mhz.
This results in a "sum" frequency of 8.895 to 8.395Mhz.
This variable frequency is then fed through the ole SB/HW
series 8Mhz transformer to a second mixer where it is mixed
with the 12.395Mhz crystal oscillator resulting in a
"difference" frequency of 3.500 to 4.000Mhz. The plate
circuits of both mixers would be tuned to either the
"difference" and "sum" frequencies using Heathkit SB/HW
series tuned circuits.

The VFO is the LMO taken from the SB/HW series
transmitter/transceiver. No crystal filters are used
and the mixers would, in receive mode, be biased to
cut off through a relay. Any 5 to 5.500Mhz VFO would
work but the tuning would be backwards; 5.500 to 5.000Mhz.

Plate modulation, again using spare Apache or DX-100 iron
etc. Final amplifier could be 6146 based but there are
other possibilities as well.

Power supplies could be based on the original SB-400/401
transformer using voltage doubling circuits to produce
all voltages including 800VDC. Using the SB-400/401
transformer would keep the size of the iron smaller
and would take up much less chassis real estate. I have
some concerns whether the SB-400/401 transformer would
handle the continous duty power or not. I thought about
an external power supply so that is a possibility.

I have an ole Apache TX-1 chassis, front panel and cabinet
that I would like to build the transmitter in. The top plate
of the Apache will be replaced with a new aluminum plate.
The front panel would be used as a template for a new front

Any comments and/or suggestions?


If you're gonna do this, why not stop reinventing the wheel and just convert a SB-400/401 to AM?  It's very easy and the results are outstanding.

Yuo're just gonna end up wiht a SB-400 on a TX-1 chassis when you're done...

I agree with Johnnie. Mod the 400 ala KD2XA's Griefkit mods and have it.
Either way you'll end up with a 25 watt carrier rig. That's all the power supplies will handle. They were made for for 100W SSB service not 100W carrier AM !

I am aware of the SB-400 AM mod but that is not what I was talking about. But that's ok.

I thought I could get some help on building a homebrew "AM" transmitter using "plate modulation",
different "final tubes", "power supply components", and controlling the frequency and biasing, using parts I
have on hand or could possibly obtain. Something that would be fun doing. But then, again, my mistake...
I should have never mentioned "Heathkit" and "SB-400" on an AM forum. For that I apologize.

Thanks WD8BIL and W3JN for your "colorful" and "unsupportive" comments, they were really uncalled for....


John and Buddly are 2 of the most helpful on this board. Thier comments were not "unsupportive", they were just suggestions on helping you make AM as easy as possible. Evendentally, you just happen to have a chip on your shoulder. There are plenty of "Heathkits" and even "SB-400's" on AM, so don't be afraid to mention those words in here(the forum).
If you have a problem with anyone on this board, PM them, don't make it public, and PM any moderator, they would be more than willing to help. If you're purpose was just to start trouble, then hit the bricks.



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