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Re: [Amps] Grid current protection HELP

To: 'Michael Tope' <>, "" <>
Subject: Re: [Amps] Grid current protection HELP
From: Al Kozakiewicz <>
Date: Mon, 13 Feb 2012 21:30:35 -0500
List-post: <">>
I think TRIG (pin 2 of the 555) is supposed to be wired to the junction of the 
100K resistor and collector of the phototransistor in the opto isolator. The 
equivalent of a "typo" in a schematic.


-----Original Message-----
From: [] On 
Behalf Of Michael Tope
Sent: Monday, February 13, 2012 9:15 PM
Subject: Re: [Amps] Grid current protection HELP

I don't see how the opto-isolator triggers anything. According to the schematic 
it switches 100K to ground on a node fed by the output of a
7815 regulator. That doesn't make any sense to me. I think there are some 
errors in the schematic. There is probably a pull-up between pin 2 of the 555 
and the 7815 output instead of just a wire, I think that creates other 
problems, so without staring at it for more time than I have tonight, I can't 
tell you exactly how it is supposed to be configured. I just can't see how it 
could possibly work the way the schematic shows it.

73, Mike W4EF..............

On 2/13/2012 4:59 PM, rick darwicki wrote:
> Hi all,
> A while back K6XX published an article that can be found at  
> It is a simple opticoupler that triggers a 555 timer base on the voltage drop 
> across a resistor.
> I built the circuit but only connected pin 2 to the 100k resistor from the 
> opticoupler.
> It has different levels of working with different connections I have tried. 
> Grounding the relay jack will key Q1 if the output is low, but it starts 
> high. At one point I could vary the voltage in to the opticoupler and trigger 
> the 555. Also, the time delay worked too. Now I can't get it to do much hi hi 
> I need to start over.
> I'm a tube and voltage guy and almost nothing I've built SS except for 
> a 160 meter surface mount SDR and my copy of the Alpha 78 QSK board 
> has worked first time out hi hi
> Can someone look at the schematic and let me know what the problem is, IE 
> correct it?
> I can see the trigger tied to B+ and do not think that is correct. 
> I assumed pin 4 needed to go to B+, maybe not.
> I made a PCB and it is a pain makeing changes and cutting foil.
> Please, any help from you solid state guys? My 8874s need you. K6XX does not 
> respond.
> Thanks
> Rick, N6PE
> ==================================
> Talk is cheap... except when Congress does it.
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