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

[J Mcvey]

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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