[John Byrns]

For the better part of twenty years I have been hearing comments that the
original source of the ³Twin Triode² transmitter design was a construction
article that had been published in Electronics Australia magazine. A reader of
this group recently sent me a copy of the Electronics Australia article, which
was written by Peter Lankshear.

I have extracted the original schematic from Peter's article and posted it here
for discussion.

http://fmamradios.com/stuff/mate%20TX%20schematic.gif

Some points worth noting, the High Voltage power supply is 250 volts, somewhat
higher than the approximately 160 volts used in the ³Twin Triode² transmitter.
The oscillator, under carrier conditions, operates with a plate voltage of 100
volts, and a plate current of 2.95 mA, for a DC power input to the final RF
stage of 295 mW, somewhat above the 100 mW limit that is allowed in the USA.

The Electronics Australia transmitter also includes an audio pre amp stage like
Flipper added to his, making it a ³Triple Triode² transmitter. Also, as Flipper
suggested, it uses a 470 pF RF bypass capacitor from the modulator plate to
ground, rather than the 10,000 pF capacitor the ASCII schematic version used.
This reduces high frequency slewing distortion as Flipper has reported.

The Electronics Australia transmitter also has the oscillator grid capacitor
connected to the oscillator cathode for DC as I suggested, so that the capacitor
doesn't have the full modulator plate audio signal impressed across it, further
reducing high frequency slewing distortion.

V1 the audio preamp can be either a 6AV6 or 6AT6, and V2 the modulator &
oscillator can be either a 12AU7, 12BH7, or 6CG7, according to Peter's article.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[John L Stewart]

Originally Posted by John Byrns

For the better part of twenty years I have been hearing comments that the
original source of the ³Twin Triode² transmitter design was a construction
article that had been published in Electronics Australia magazine. A reader of
this group recently sent me a copy of the Electronics Australia article, which
was written by Peter Lankshear.

I have extracted the original schematic from Peter's article and posted it here
for discussion.

http://fmamradios.com/stuff/mate%20TX%20schematic.gif

Some points worth noting, the High Voltage power supply is 250 volts, somewhat
higher than the approximately 160 volts used in the ³Twin Triode² transmitter.
The oscillator, under carrier conditions, operates with a plate voltage of 100
volts, and a plate current of 2.95 mA, for a DC power input to the final RF
stage of 295 mW, somewhat above the 100 mW limit that is allowed in the USA.

The Electronics Australia transmitter also includes an audio pre amp stage like
Flipper added to his, making it a ³Triple Triode² transmitter. Also, as Flipper
suggested, it uses a 470 pF RF bypass capacitor from the modulator plate to
ground, rather than the 10,000 pF capacitor the ASCII schematic version used.
This reduces high frequency slewing distortion as Flipper has reported.

The Electronics Australia transmitter also has the oscillator grid capacitor
connected to the oscillator cathode for DC as I suggested, so that the capacitor
doesn't have the full modulator plate audio signal impressed across it, further
reducing high frequency slewing distortion.

V1 the audio preamp can be either a 6AV6 or 6AT6, and V2 the modulator &
oscillator can be either a 12AU7, 12BH7, or 6CG7, according to Peter's article.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

Similar to what I had in mind. There are only so many things one can do with a couple of vacuum bottles. I would add an RFC on the modulator plate. And to avoid incidental FM a seperate oscillator to drive the final RF. Still all in two bottles.

Now that a succesful couple of circuits have been proposed do you intend to build your own?

Cheers, John