[Milsurplus] GO-9 Progress 7 Nov. 19: "Two Birds With One..."

[Richard]

Another bias option:  Many years ago I submitted to QST for Hints & 
Kinks a way to get a bias voltage at no additional cost.  It went into 
their black hole for five years where-upon I got a call one night from 
one of them asking further questions.  It was then published and used in 
their Economy Power Supply for several years.  Briefly; put the B+ 
filter choke in the minus lead to ground and rectify the ripple voltage 
across the choke to get a negative voltage.  As long as a few mills are 
going through the choke the ripple voltage and bias voltage are pretty 
constant.  it will be about 40% of the B+ voltage, but can be divided 
down.  If you don't want significant voltage at the key you can use any 
small relay. (At that time I think publication was run by a bunch of 
kids, and if it didn't interest them it didn't get published.)

Richard, AA1P

On 11/8/19 9:01 AM, David Stinson wrote:
> GO9 Transmitter Progress 7 Nov 19:  "Two Birds With One..."
>
> Not counting the improvement needed in the modulation scheme, two 
> system functions still needed to fully stand-up the GO-9 transmitter: 
> Grid-Block keying and antenna TR switching.  Tests showed that a 
> low-current source of at least 80-90 negative Volts is needed to fully 
> cut-off the three stages.  Don't relish the idea of adding a 5th 
> transformer to this project for a bias supply.
> Been ruminating on the problem all day until I remembered I had a 115 
> VAC Dowkey Relay in "The Cave."   Since the relay is designed to be 
> driven directly from the 115VAC primary power, the coil will work on 
> rough half-wave rectified DC as well as AC and the grid circuits at 
> cut-off draw practically no current, this presented a simple solution 
> for both problems.
> Here is the circuit:
> https://photos.app.goo.gl/uM9hkA23kqcT5kz58
>
> Since U.S. house current is supplied "Hot/Neutral," Neutral being 
> grounded, a half-wave rectifier and a crude filter in the "Hot" lead 
> (fused of course) easily provides the potential needed to both drive 
> the relay and bias the grids.  The connection to the transmitter with 
> the key up is essentially an open circuit, so a meter reads about 
> -160VDC at keying/grid bias point 17.
>   When we close the key, the grids are grounded, keying the 
> transmitter and closing the circuit of the Dowkey relay. On-the-air 
> tests work well.
> Down-side:
> This puts rectified line-voltage on the key contacts.  My intent is to 
> introduce a MOSFET at this point, so the key has only the low MOSFET 
> gate voltage on the contacts.  Still work to do.
>
> GL OM ES 73 DE Dave AB5S
>
>