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

[John Coleman]

	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.  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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