Globe King 500 Mods

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W1LSB:
Hi all:
Just wondering if anyone has really dug into a Globe King seriously.  I've read everything I can find, including the AM Press Exchange and ER, and there's not much out there on performance improvements.  The typical operating points aren't based on anything that Eimac or Amperex ever printed.  As these rigs were shipped by Leo & friends, the PA plate volts are too low, and the mod plate volts are too low, and that's just the beginning.  The PA is not neutralized, cooling is marginal, and bias and screen supplies are lame.  Everyone complains abut RF output; mine is 250W at best.   Sure as hell looks nice though!

I'm thinking that the screen supply, bias supply and plate supply all need some serious changes to get this beast working even close to it's capability, and wondering if any of you have been there first. Most people seem content to do some amount restoration and fire 'em up as they are, with mods in the audio chain.  Mike Cowart, WA5CMI, got carried away, but what a nice job he did with his 500. Mike uses external audio up to the 811's, but everything else is pretty much stock. 

Funny thing is, it's pretty similar to the Viking 500, but vive la difference. 

Thanks & 73
George - K1GXT

Jim, W5JO:
George your obversations are correct.  But considering most people want them stock so as to preserve the appearance they do a fair job.  My 500A puts out 320 watts on 75 meters and modulates about 90-95% on negative.  It is real close to 100% positive.

A friend of mine has a C model he just acquired that has had the B+ to the 811s increased and the audio chain modified to replace the couplates and it didn't make a lot of difference.

You will find the coils in it also loose inductance after about 20 minutes operation because they get hot.  On 160 it is a comprimise at best, but it does give a good account of itself with the 300+ watts out.

Mine does 250+ on 10 meters and 15.  Strangely enough it does best on 40 giving me about 350 watts out.  I guess one could do all you outline, but if you are going to do that, why not homebrew a complete set and sell the GK for cash.

nq5t:
One can point out all of the bad things about this radio, and there are certainly a few, and they have been discussed considerably.  As far as how much better the Viking 500 might be,  I've heard a lot of both, and frankly, the V'ing-500 doesn't play any better.

The GK runs well and puts out a more than decent signal without many changes (I get about 290W carrier out and can moduulate at about 110% without observable distortion). 

1.  Lose the couplates
2.  Feed the audio chain into the "phone patch" input with transformer isolation.
3.  Lose the Eimac 4-400A/4-250A and use an Amperex graphite tube.

It isn't a 20V-something, but it never claimed to be ... :-)

By springtime, I wil be driving the modulators on mine with a modified  Eico 730, adding a mod choke, replacing the mod transformer, and rebuilding the tank circuit.  It will be interesting to see what the observable differences are, if any.  While the GK-500 is torn down, I'm using a GC-300, with very heavily modified audio.  Nice radio!

Either of these radios sound good.  To get out of the 50's., none of them sound any better, or seem to be distinguishable from, a Ten-Tec Orion/Orion -II into a pre-MFJ AL-1200.   Frankly, I wish I had the time and inclination to build a class E rig for 20/40/80.  Any multi-million $$ contributions to my retirement account would be appreciated.  I accept PayPal -- minimum contribution $500K :-)

Grant/NQ5t
http://www.globeking.com

W1LSB:
Hi Jim:
Sounds like yours is running pretty well.  I have to agree with you on the idea of keeping it relatively stock.  The mods I've been considering don't include any hacking on the sheet metal, just a few minor circuit changes that could easily be reversed if need be.  

If I get to 320-350W, on AM with 90%, I'd be  happy.  One problem is that some of the iron has been changed.  The PA plate xfmr was replaced at some point by a new WRL component with the same part number, but's physically smaller than the original and needed different mounting holes.  My HV probe is broken, and it's keeping me from getting a good handle on B+ to the PA. Have a new probe on the way, so should know soon.

One thing I've noticed is that full plate loading to 320 mA cannot be acheived with either a  4-250 or a 4-400 in the socket. It behaves like the grid drive is low, but it's not - and all of the multiplier resistors are new, which really makes me suspect the HV.  Using 3B28's at the moment, but thinking about mounting some K2AW diodes under the chassis.  


Oh well, I guess persistence is in order !!!   BTW, the home brew idea is also pretty interesting. I just love these 4-400's !!!

73, George - K1GXT
  

Jim, W5JO:
Well they are good rigs for the time they were built.  I remember hearing them back in the mid 50s and they were right up there except for the guy with the home brew KW.  Now he had a siganl.

I see 1850 volts on the HV connector going into the RF chassis with my probe in transmit.  Are you sure the final tubes you are using are good?  Have you checked the 22 ohm metering resistors?  They can change value but probably haven't.  What about the screen current?  If the screen current (voltage) is low, you will see low output.

I modulate mine the stock way because I don't have a radio voice, so there is no use in adding a lot of low frequencies.  Another thing you might have noticed is the design of the tank circuit is not the best.  It barely will make a match to 50 ohms on 75.  Moving the load cap will only change the plate current about 20 mils at most.

Straight from the coax connector the only real change in plate current is the antenna coupling switch on 75meters.  I bought a good quality 6:1 balun in a box and mounted it on the RFI shield near the coax connector.  Then took a banana plug and ran into the center of the coax connector.  I then tied it to one of the 300 ohm terminals on the balun.  The other therminal I tied to ground, using about 1" wires for both connections.  That gives me nearly 50 ohms for my antenna.

The output circuit likes that much better.  But if you do that, get a high quality, high power balun and don't use it above about 14 megacycles.  Also be sure you don't load into an open or short in any case.  With that set up I see the 320 watts out no problem.  The max output occurs with the plate meter reading 315 mils when I first turn the transmitter on and then drops to around 300 mils for that power level.  If you do the balun trick, measure it from the 300 ohm to 50 ohm with an MFJ 259 to see if you are going to get a good match before trying it.

As Grant said, it is a good radio, almost bulliet proof if run correctly.

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