To paraphrase a famous line from the movie Casablanca, I’m shocked Mark, I

tell you shocked!  The GF-11 is an early 1930s low power command set with a two tube MOPA RF arrangement , and a pair or type small type 10 triodes.  Perhaps yours has been modified use as  a phasing type single sideband exciter in the early days of amateur SSB in the late 1940s-early 1950s.  In that case I would expect there would be evidence of considerable modification, including a phased shift network and a  balanced modulator and a pair of carrier null potentiometers. Or perhaps it’s just a dummy switch added as a joke or prank back in the day.

That said, MOPA sets like the GF-11 can in fact transmit a signal that has one sideband that contains significantly more energy than the other.  These sets usually generate significant incidental FM along with AM on voice, and there is a lot a phase cancellation going on.  The BC-375 and 191s are notorious for this behavior.  If you look at the spectral and waterfall display of one of these transmitters in voice mode you will likely see that the majority of the modulation is on one sideband. We once had 4 such sets on in a net and some were generating mostly upper sideband modulation energy, and some were mostly lower sideband, all with full carriers of course.  You  need a balanced modulator to null out the carrier and select the desired sideband you want your SSB to be on.  With careful neutralization and finessing of the PA plate current dip you can get reasonable sideband energy balance in AM operation.

Here’s a good link that describes the GF-11 in detail:

https://www.radioblvd.com/RU16-GF11_Restoration.htm

  Send us a pix of yours if you can!

73 de Chris AJ1G

Stonington CT

Sent from my iPhone

On Jul 18, 2023, at 16:04, Captain D. <[email protected]> wrote:



Open the Tube compartment cover, and near the back of the divider between tube compartment and the rest of the radio you will see the toggle switch that can turn on either upper sideband or lower sideband

 

Mark D.

WW2RDO

In a message dated 7/18/2023 7:12:20 AM Eastern Standard Time, [email protected] writes:

 

Well, now that you’ve got our attention, please tell us more!

Chris AJ1G
Stonington CT

Sent from my iPhone

> On Jul 17, 2023, at 18:26, MARK DORNEY via MRCA <[email protected]> wrote:
>
> I was surprised to find a small toggle switch in the GF-11 transmitter that allowed for operation on either low sideband or high sideband.
>
> Mark D.
> WW2RDO
>
> “In matters of style, float with the current. In matters of Principle, stand like a rock. “.  -  Thomas Jefferson
>
> Sent from my iPhone

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