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Feedback out of relay

S

Skyscraper

Member
Jun 6, 2005
24
0
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Homebrew 16 pill with as little as a 100 watts drive I get feedback from the relay. With very little watts drive no feedback until you talk. Any sugesstions?
 

Its possible the contacts inside the relay are resonating and causing interference. Try upgrading to a larger relay. Another possibility is that the relays contacts are not shielded from one another and that the input contact is sensing the output contact and it is going into what is known as self oscillations. A tell tale sign of this is occurring would be the amp staying keyed after the exciter is removed(radio unkeyed) In any situation I would upgrade the relay. This brings me to a question though, How do you know the relay is causing the feedback? A little more information would help to solve this problem but I have given you my to most common answers!

As a side note: A relay with a high impedance contact can also cause excessive strain on the transistors causing a load mismatch and possible feedback.
 
By buzz, do you mean chattering? Put your finger on the plastic case of the relay and key the exciter. If it feels like the relay is closing and opening at a high rate of speed then there are two likely conditions to cause this. One, is that the amp is drawing more power than the supply can handle and voltage is dropping off to the point of the relay's coil is no longer able to stay energized. This can be tested by checking the voltage supplying the relay (or even feeding the amp) and make sure that when keyed the amps supply voltage does not drop below 12v (11v at most). If it does than you need a larger power supply. Another idea would be that the coil inside the relay itself is bad and that you need to simply replace it. Those are the easy things to llok for and attempt, There are other more tricky problems that could be involved such as the keying transistor or diode have blown or the rf is disturbing the coil. Keep us posted!
 
Thanks for the info. It might be the keying transistor.I used a 2N3906 PNP. I got the at radio shack. it says it is for general-purpose amplifier and switching applications. I belive my problem is the keying circut maybe that's it. I would like to see a pic. of a keying circut built the right way! Thanks for any info.
 
sky do you have any pics of the inside of the amp, maybe somebody can spot something that may be causing you problems??
 

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