[AMRadio] WTB: WRL Globe King 500-C (or A)

Tue Apr 23 15:03:14 EDT 2002

John,

>
> 	I don't know much about GKs but I do know that the
> plate efficiency of a
> class C plate modulated rig should be independent of plate
> voltage.

I don't think so.
Not in real life.

If I have a 4-125 tube, and run it at 500 volts on the plate,
I am not going to get 300 watts out, as the plate current
would have to be 800 ma, which the tube wont do.

If I run it at 2000 volts, and get the plate to show
its rated color (very bright orange), I got about 275
watts out.
If I ran it at 2500 volts at the same color, I got over 300
watts out.

If I could have run it at 3000 volts, I bet it would put out
even more power.

I remember doing a chart on the globe king 500, and the higher the plate
voltage, the higher the efficiency and output power.

I notice the same thing on the push pull 811 rig
as well...much more power output at 1700 volts, than at
1200 volts for the same plate dissipation....

What am I missing?

Brett
N2DTS

That is
> if the Plate efficiency is 70% it should be 70% at all plate
> voltages.  This
> must be true, else the RF output voltage will not follow the Plate
> modulation voltage resulting in harmonic distortion of the audio and
> intermodulation distortion in the RF causing unwanted
> sideband energy.  If
> the RF output voltage is 20 volts PEP when Ep = 500VDC the it
> should be 40
> volts PEP output when the plate voltage is 1000VDC.  If this
> is not true
> then there is a problem with other parameters (drive and bias
> probably) that
> is at fault.  I have heard this many times about various
> tubes but I have
> never any such trouble. Every one told me not to run 304TLs
> as they needed
> so much voltage to work but I found that they worked real
> good at 1700 volts
> and 600 ma with 80+ % efficiency.  I did have to use a larger
> than normal
> capacitance in the output tank to achive the proper Q and the drive
> requirements were quite high untill I changed to 304THs. The
> 304THs were not
> quite as efficient as the TLs but the efficiency did not
> change with any
> setting of the variac that controled the plate voltage using
> either tube.
>
> GL, 73, John, WA5BXO
>
> -----Original Message-----
> From: amradio-admin at mailman.qth.net
> [mailto:amradio-admin at mailman.qth.net]On Behalf Of Brett Gazdzinski
> Sent: Monday, April 22, 2002 7:21 AM
> To: amradio at mailman.qth.net
> Subject: RE: [AMRadio] WTB: WRL Globe King 500-C (or A)
>
>
> Don,
>
>
> > I dislike the under-rated components in the rf final, and the
> > under-rated
> > modulator.  Neither transmitter would ever make more than 85%
> > positive peak
> > modulation no matter what we did.  The final amp runs too
> > much plate voltage
> > compared to the modulator (1800 volts on the final, 1250 on
> > the modulator,
> > as I recall).
>
> What I did not like was the low voltage used on the rf deck.
> 1800 volts on a 4-250/4-400 is very inefficient!
> They want 2500 volts at least.
> I got 300 watts out with 540 in.
>
>
> The globe king 500 is one of those transmitters where everything
> seems very marginal, and cries out for re doing.
> I was very unhappy with mine, used just the RF deck for a while,
> then took it all apart for parts.
> I gave many of the parts away to other globe king owners,
> and think I wound up giving almost all the parts away.
>
> Its just one of those rigs I could not deal with, the whole
> design was based on making it inexpensive.
>
> The power supplies needed serious help, all the iron was light,
> the mod transformer was not good, the rf deck used small
> low voltage parts, and should have used a different tube setup
> (lower impedance tubes), and what was up with putting the
> 160 meter coil under the chassis?
>
> I agree the GK 400 was a much better transmitter in every respect,
> although they also needed a lot of work to get them working
> well.
>
> Today, a 300 watt output transmitter is a nice piece,
> but a $1000.00 or more Globe King 500 is shocking to me.
> Its very hard to get used to the prices these days.
>
> I guess the best thing to do is save one as a collectors piece,
> as they are worth some money now.
>
> It seems pointless to me to take something worth so much
> money and modify it.
> Pushing much more audio through it, or trying to get it
> to pass bass frequencies is likely to cause lots
> of problems with hum and arc overs and blown mod iron.
> Maybe running it at 200 watts out and moderate fidelity
> would do.
>
> I don't hear much WRL equipment on the air anymore.
> I don't think I ever heard anyone using a globe champion 300.
> They LOOKED cool, but had their own problems I guess..
>
> Brett
> N2DTS
>
> >
> > Don K4KYV
> >
>
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