[Amps] Grid current protection HELP

Michael Tope W4EF at dellroy.com
Mon Feb 13 20:15:43 PST 2012

That would make more sense, Al. There is also the issue with figure 2 in 
the article (the reflected power protection interface). It shows the 
output of the comparator going to pin4 of the 555 timer, but in figure 1 
pin 4 is shown connected to the regulator output, so there must be an 
error there as well. Perhaps it is supposed to be implicit in his 
instructions that pin 4 gets disconnected from the +15V buss before it 
gets connected to the output of the comparator. Even so, using the reset 
pin for excessive reflected power wouldn't make sense. What I think 
would make more sense is if the comparator (+) and (-) sense inputs were 
reversed and the comparator output was connected to pin 2 of the 555. In 
that case, the series diode in the output of the comparator circuit 
would have to be reversed so that only allowed the comparator to sink 
current into its output when there was excessive reflected power. K6XX 
must have forgotten to incorporate a bunch of red lines into these 

Mike W4EF.....................

On 2/13/2012 6:30 PM, Al Kozakiewicz wrote:
> 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.
> Al
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On Behalf Of Michael Tope
> Sent: Monday, February 13, 2012 9:15 PM
> To: amps at contesting.com
> 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
>> members.cruzio.com/~k6xx/radio/76a_prot.pdf
>> 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
>> ==================================
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