[Amps] Pin Diodes

[W0UN -- John Brosnahan]

At 05:45 AM 3/8/2006, Paul Christensen wrote:

> >  I don't believe an amp with vacuum relay T/R
> > switching can be considered a full QSK amp.   Yet Alpha advertises the
> > 99 and the 9500 as full QSK.   I run my 99 in semi-breakin only. How
> > long can a vacuum relay last in full QSK mode?
>
>The vacuum relay in my Alpha 70V has lasted 36 years.  A vacuum relay with
>an appropriate accelerator circuit can switch nearly as fast as a PIN diode.
>
>Paul, W9AC


Paul, I think your experience with relay lifetimes is pretty typical 
of amps used
on a regular basis in normal operation and is shared by many of 
us.  But I suspect
that if an amp is operated in a CW contest every weekend and used during the
week by a high-speed CW merchant for a lot of rag-chewing then the relay life
may not be nearly as great.

I do quibble with your statement on speeds.   Vacuum relay speeds are 
measured in
milli-second switching times whereas PIN diodes can be switched in 
micro-seconds.
The fact that PINs are not switched that fast for typical ham amps is 
more of a function
that they don't need to be rather than that they cannot be switched 
that fast.  Of course
it all boils down to the operating frequency and the carrier lifetime specs.

73  John  W0UN