[ARC5] GO-9 Progress 7 Nov. 19: "Two Birds With One..."

[Scott Robinson]

A 6V relay and a junque box filament transformer would sort this out 
niceley.

/scott

On 11/8/19 7:18 PM, J Mcvey via ARC5 wrote:
> 
> Also, a mosfet will not guarantee isolation . An opto isolator would be 
> better suited for the isolation function, but they can't handle the 
> voltage directly , so perhaps use an "opto" to drive the mosfet?
> 
> On Friday, November 8, 2019, 10:53:39 AM EST, J Mcvey via ARC5 
> <arc5 at mailman.qth.net> wrote:
> 
> 
> The only problem with that is you are exposed to the rectified line 
> voltage when the key is open . Line > rect > coil resistance > YOU > 
> ground. ( ouch ... or DEAD)
> One of birds you might be killing is YOU.
> I'd find a better way to isolate myself from the line in a better way.
> Even if you used a LV relay to actuate the the AC, it would be more 
> safe. However, applying line directly to ground is not a recommended 
> thing to do either.
> For example , what if the house wiring was reversed L and N ? You have 
> full current line on the metal box!  ( I have renovated enough houses to 
> tell you that mis-wiring is all too common!)
> I refuse to repair certain old ( ancient) ac/dc radios that had similar 
> schemes unless they agree to install an isolation transformer.
> 
> On Friday, November 8, 2019, 9:02:33 AM EST, David Stinson 
> <arc5 at ix.netcom.com> 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
> 
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