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Re: [Amps] How to read the 3-500Z spec sheet?

Subject: Re: [Amps] How to read the 3-500Z spec sheet?
Date: Sun, 23 May 2010 10:29:04 EDT
List-post: <">>
Rob, You have to remember that the tube ratings are for CCS not SSB or CW  
service.  CCS service is 100% duty cycle, SSB is 30% duty cycle and CW is  
about 45% duty cycle.  It is not the higher plate current nor the higher  
grid current during the cycle that kills the tube, it is the constant over the  
top plate dissipation that kills the tube.  Running an AL-80B at 1000 watts 
 output on SSB will barely show much anode color compared to the same anode 
color  at CCS rating at 750 watts output.  That amp was rated by it's 
designer  W8JI and he sure knows what he is doing.  I tend to agree with him 
since I  pay close attention to the tube anode color with a pair of 3-500's 
running at  1500 watts PEP on SSB.  Although that would be in the rating of the 
tube  anyway.  In fact henry I believe rated one of their 3-500 amps at 2000 
 watts output on SSB, so that is in line with Ameritron's claim.
In a message dated 5/23/2010 10:18:54 A.M. Eastern Daylight Time, writes:

you say  you are getting 400 w. with 520 ma Ip.  I think that's 120 ma
over the  max Ip for a single 3-500 so you're possibly in trouble  right

you say you increase drive and get no more suds which  means the tube
is probably saturated.

An AL-80B on any band putting  out 900 w. is a bad idea regardless of
what Ameritron says.  It is a  lot easier to _sell_ a "1 KW amp" than
it is a 700 w. amp, which is what  the AL80B really is (actually that
power output is optimistic) unless you  don't mind getting a new 3-500
every few years.   If you consider  the max rated plate current of a
single 3-500 (400 ma) and look at the  specified power supply v. in
that amp (2700 v. no load as I recall) and  figure it sags down to 2400
under load and assume 70% efficiency (giving  them the benefit of the
doubt) you get a choice of either abusing the poor  single 3-500 or
discovering some promotional hype license is being taken  (In ham
radio?  You gotta be kidding me!).   That amp is  probably what is
keeping 3-500zg rolling out of some tube plant in China,  so maybe we
should all be glad.   Every time I work some ham  operating that amp
and driving it over 700 w. I politely tell him what's  happening and
get either anger or the guy never comes back to  me.   3-500 used to be
sort of cheap for the watts but they are  getting expensive now.  Oh
well it's not my money.

But, back to  your point, I'd drop the drive down to where you are
getting < 400 ma on  the plate and be happy.  How much power does it
take to have a QSO on  6 m. anyway.  I have never operated that band
but I thought the "magic  band" either let you have a QSO with 59 copy
and 1/2 watt, or no amount of  power would get through.  Nothing in

As for 100%  duty cycle, if the cooling is stock, you probably want to
put in a fan that  moves more air.  No matter what you do, 520 ma is
too much plate  current.


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