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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?
From: Vic K2VCO <>
Date: Sun, 23 May 2010 08:30:42 -0700
List-post: <">>
Regarding the 400 ma rating, I've often wondered why it matters as long as the 
dissipation is not exceeded. The only thing I can think of is the possibility 
that the 
filament emissive ability could be damaged in some way.

I prefer the metal-plate 3-500's just because the color is a very responsive 
indicator of 
plate dissipation.

By the way, I have some carbon-anode 813's and one of them apparently was 
overloaded at some point. The carbon shows lots of little pits, sort of 
reminiscent of a 
road sign in rural Texas.

On 5/23/2010 8:16 AM, Carl wrote:
> 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
> remember.
> 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.
> Carl
> KM1H
> ----- 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

Vic, K2VCO
Fresno CA
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