[Boatanchors] Seeking Transmitter Design Suggestions

[Rob Atkinson]

That transmitter has some odd design flaws.  The output pi network
uses a tapped down 40 µH coil and a pair of ~300 pF air variables.  It
was designed to work into a 300 or 400 ohm line.  For normalized 50
ohm line and load, the output network has to be modified.  Not really
a flaw since in its day, a lot of hams used twin lead.    I recommend
replacing the pi network coil with air dux.   The stock coil is wound
on thin phenolic tube.  If the rig is keyed down for a minute or more,
the coil heats up and the form starts to smoke.

The final PA is keyed by completing the plate supply return to the CT
of the transformer and grounding the - side of the filter capacitor
through the CW key.   This results in an almost square wave rise on
the keying RF envelope.

In my opinion, these issues may have to be resolved before it can be
used as a regular CW rig.

Mine also has RF in the FM broadcast band.  My experience with these
panel mounted air variables is that they have to be strapped directly
to chassis ground using low inductance strap, not wire.  Avoid braid
also.   Doing that usually stabilizes and cleans up 807s.

73
Rob
K5UJ

On Tue, Nov 16, 2021 at 2:32 PM JAMES HANLON <knjhanlon at msn.com> wrote:
>
> The WRL Globe Chief 90 was/is a 90 watt, 160 through 10 meter bandswitching CW-only rig using a pi-match output.  It has a 6AG7 crystal oscillator driving a pair of 807s in parallel and a 5U4G rectifier.  It would be a good rig to look at for some design ideas, especially if you are thinking of using 807s or 1625s.  You can get a manual for it from the Boat Anchor Manual Archive at https://bama.edebris.com .  From the home page select WRL, and then Chief90 from the next screen.  There are manuals for a lot of other good vintage rigs there as well.  Another to look at would be the Eldico TR-75-TV5, a 6AG7 to single 807 rig using pug-in coils.
>