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

To: <>, <>, <>
Subject: Re: [Amps] How to read the 3-500Z spec sheet?
From: "Carl" <>
Date: Sun, 23 May 2010 11:16:49 -0400
List-post: <">>
At 2700V @ 400 ma it doesnt matter if its CCS or not, thats all the tube 
will do safely in SSB service especially in an AL-80 series with marginal 
cooling. Anything over 700W or so is pushing its longevity.  Ameritron 
doesnt care that the manual says 600ma and 1000W PEP, they sell tubes 

And dont try and judge a safe color with a graphite anode, there shouldnt be 
any in SSB service and only for a short time during tuneup.

I wouldnt consider a Chinese tube at CCS anyway over 2200V.


----- Original Message ----- 
From: <>
To: <>; <>
Sent: Sunday, May 23, 2010 10:29 AM
Subject: Re: [Amps] How to read the 3-500Z spec sheet?

> 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
> there.
> 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
> between.
> 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.
> 73
> Rob
> K5UJ
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