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

[Rob Atkinson]

Hi Lou,

I saw ur setup at Dayton but I didn't have time to stop and say hello.
 Sorry about that but I'll make a point to do so next year.

A few points:  I don't know what Rauch did or didn't do--for one
thing, I have no idea what the original AL80 was specified to do but
I'll bet if Rauch did design for a 1 KW output amp from a single tube
he assumed low duty cycle and not the maximized processed super
compressed garbage SSB I hear all over the bands now, which is not any
15 to 30% duty cycle.  Ten Tec sells some kind of nasty speech clipper
now where they claim almost 6 dB increase in average power for SSB.
With a 100 w. exciter that's taking average 20 w. and making it almost
80 w. average.  Yikes, must sound beautiful.

Henry's 3-500 amps all had Ep up near the 4 KV maximum--there is a big
difference between that and the AL80B and this guy's amp.  I think the
henry p.s. sagged to 3600 v. under load.  pair 3-500 let's say max Ip
800 ma you get 2900 w. input @ 70% efficiency you get 2 KW out and the
tubes are under their maximum plate dissipation.  So, you are correct
in saying this guy should have a higher Ep.

Let's look at his situation.  I think he has 1.95 KV.  520 ma.  I get
a little over 1 KW input.  He says he has 400 w. out. Then the tube is
dissipating 600 w.  Okay, maybe not all the time.  If he is running
gentlemanly SSB and has a lot of fan maybe he is okay if we follow
your thinking.

I freely confess to being careful and conservative, perhaps to a fault.

If he is overdriving the amp and/or has a lot of heavy processing
things may not be so good.   If he is running his data mode which is
100% d/c then the tube seems to be dissipating 100 w. over its limit
for the whole transmission.


73

Rob
K5UJ




On Sun, May 23, 2010 at 9:29 AM,  <Gudguyham at aol.com> wrote:
> 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,
> ranchorobbo at gmail.com 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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