[Amps] Alpha 87A reliability problem

2 2@vc.net
Thu, 2 Jan 2003 08:34:46 -0800


>My otherwise excellent 87A is too often out of service due to PIN-diodes
>breaking down.
>
>Has somebody ever made a modification with vacuum relays instead ?
>
I have not, Rag, but this seems like a good idea since PIN diodes are 
easily shorted by lightning and by high SWR.  However, for >40wpm CW, 
relays are not fast enough.  Modifying with high-speed relays also 
presents an opportunity to remove the  RF-actuated T/R switching and use 
a transceiver-actuated electronic cathode bias switch (ECBS).  This will 
result in the bias switching always being in perfect sync with the RF 
switching, which will stop the tubes from being switched in and out of 
linear bias in the middle of soft-syllables and making rough-sounding 
audio.


good luck

>
>73  HNY
>
>Rag Otterstad    LA5HE also JW5HE OZ8RO
>located in Telemark - home of skiing.
>
>My antenna "farm" can be found on HTTP://no.photos.yahoo.com/la5he when you
>click on  Radio.
>
>
>Take a look at: http://WWW.visitTelemark.com
>
>or  http://www.visitnorway.com
>
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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