[TowerTalk] Protection of a preamp

Patrick Greenlee patrick_g at windstream.net
Tue Jan 21 11:25:08 EST 2014

Well that is one way.  Another is to use a (one, 1 , ein un) Zener diode to 
subtract out the difference.  Another way is to measure the current draw of 
the amps when operated on proper voltage and then calculate the value of a 
series resistor required to drop the excess voltage at that current.

For your convenience:  I=E/R   P=IE (don't forget to calc the power 
dissipated by the R so you can size it (them if you use more than one.)

A cap across the power connections at the amps won't hurt but probably not 

Patrick NJ5G

-----Original Message----- 
From: Lizeth Norman
Sent: Tuesday, January 21, 2014 10:14 AM
To: towertalk
Subject: [TowerTalk] Protection of a preamp

Hi all!
I have a preamp that I switch in and out with a pair of spdt coaxial
relays. The NC positions pass through and the NO positions hold the preamp.
The relays are +24Vdc and the preamp needs ideally 12Vdc.
Presently, I have the preamps hooked up to +24Vdc and they are frying.
What I'd like to do is when I key the relay, also feed the preamp through
20 diodes to drop the Voltage to something respectable. Possibly using a
100uF cap across the preamp.
Am I asking for trouble? Do dragons live here?
Norm n3ykf

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