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Author Topic: Globe King 500 Mods  (Read 19937 times)
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W1LSB
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« on: October 04, 2005, 01:51:18 PM »

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

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Jim, W5JO
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« Reply #1 on: October 04, 2005, 03:08:11 PM »

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.
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nq5t
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« Reply #2 on: October 04, 2005, 09:53:48 PM »

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
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W1LSB
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« Reply #3 on: October 04, 2005, 10:23:35 PM »

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
  
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Jim, W5JO
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« Reply #4 on: October 04, 2005, 10:43:51 PM »

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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W1LSB
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« Reply #5 on: October 04, 2005, 10:45:20 PM »

Good suggestions & info Grant, thanks.....  

I do have an Amperex 6156 as well as an Eimac 4-400A, so at least I'll have some good comparisons.  

Those Globe Champs are really nice transmitters.  A friend of mine had one in the early 60's, and his audio always sounded great.  Every so often, I wish my 32V-3 would turn into one, then I come to my senses !!!!  

Let us know how your 500 RF deck turns out !

73, George - K1GXT
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Todd, KA1KAQ
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« Reply #6 on: October 05, 2005, 02:30:52 PM »


Mike Cowart, WA5CMI, got carried away, but what a nice job he did with his 500.


Is that the one Gary Harmon had? If so, he had offered it to me before selling it to Mike because he knew I was interested, but discouraged me as best he could with the description. I think he didn't want me shipping it or driving all the way there to be discouraged by the condition. It was RUSTY all over, obviously from sitting somewhere damp for an extended period. The restoration job was/is still incredible. It definitely went to the right guy.

I've always liked the looks of the GKs, especially the older 400 with the bakelite meter bezels. Some years ago I ended up getting a 'slightly used' NOS cabinet for a 500. The fellow who had been using it had metal panels laid side to side across the inner chassis supports, using them as shelves. It sat atop his operating bench, the only radio device on it was an old Waters/B&W rotary coax switch attached to one of the screw holes. Even has the back door on it. Someday I want to find either a set of old chassis and panels or make new ones to fit it, and build up a HB version.

Visually I'd like it to follow the GK though. Very 'radio' looking, and Leo's WRL emblem has to be the best emblem used on ham gear.  Cheesy


* GK400_B4.jpg (21.95 KB, 328x396 - viewed 922 times.)

* GK400_after.jpg (62.55 KB, 290x372 - viewed 1072 times.)
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W1LSB
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« Reply #7 on: October 05, 2005, 03:01:10 PM »

Yup, it's the same one Todd!!!  Mike goes through the whole process on his web site, which is quite a tribute to the Globe King in itself.  Check it out ... http://home.att.net/~wa5cmi/gk500.htm

I met Mike a few years back at a CCA meeting in Dallas, and saw his photo album; pictures of the restoration in great detail.  Mine is a 500B, and not as retro looking as the earlier models, but it definitely has an awesome presence.   

Truth be told, I had a Globe Chief 90 when I was a novice in 1958, and I've had a real soft spot for WRL radios ever since.  Owning this 500B is a life long dream, so I plan to make the best of it!!

As for your cabinet - super !!  Keep your eye on ePay.  I do see GK decks for sale once in a while, but of course not inexpensive.  Mine is missing the back door, but one will turn up someday.

73, George - K1GXT
Long live WRL / Globe rigs !!
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David, K3TUE
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« Reply #8 on: October 05, 2005, 07:10:42 PM »

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.

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.

I was just reading some things about the Globe King 500 on the net.  This transmitter (as well as others in the Globe lone) strikes me as not only powerful and rugged, but also seems relatively simple and easy to understand in design.  Despite all of this, should I assume it is not a good one to start off with?  Or is Jim's comment about homebrewing one as good advice as any for a first Plate Modulated transmitter.

Maybe I'm just thinking too big.

Opinions welcome.
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David, K3TUE
Jim, W5JO
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« Reply #9 on: October 05, 2005, 10:09:39 PM »

The Globe King is a good basic design and fine to start with as long as you remember basics.  You are using 1800 volt at .3 amp.  Because of the construction of the final tank, it cannot stand much mismatch.  Make peliminary adjustments in the tune position before switching to full output.  Be sure you tune the oscillator and buffer to the correct frequencies or you will have a strong second harmonic, and that is about it.

By building your own, I ment you could avoid the little deficiencies you mentioned in your first post.  The King does have a annoying bit of hum on the carrier, but it is low and mostly won't be heard by the receiving station far away.  This is one of the things you can avoid.

By all means the King is a good first higher power tansmitter.  I like mine and wouldn't trade it.
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K1MVP
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« Reply #10 on: October 05, 2005, 10:30:20 PM »

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.

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.

I was just reading some things about the Globe King 500 on the net.  This transmitter (as well as others in the Globe lone) strikes me as not only powerful and rugged, but also seems relatively simple and easy to understand in design.  Despite all of this, should I assume it is not a good one to start off with?  Or is Jim's comment about homebrewing one as good advice as any for a first Plate Modulated transmitter.

Maybe I'm just thinking too big.

Opinions welcome.

Hi Dave,
Being a "conservative",--I believe in starting at a "lower level" and working up
to the "higher level", so I would not consider building a 500 watt transmitter
a good "first project".
I would think building a 75 to 100 watt plate modulated transmitter a much
better "first" rig to learn and get the "feel" of what is involved,--and you also
can have a lot of fun with a lowered powered transmitter on the air.
Just a few of my thoughts,--and it will be a lot easier to find parts for
a lower powered rig.
                                          73 , Rene, K1MVP     
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David, K3TUE
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« Reply #11 on: October 05, 2005, 11:08:28 PM »

Being a "conservative",-- [...]
I would not consider building a 500 watt transmitter a good "first project".
I would think building a 75 to 100 watt plate modulated transmitter a much
better "first" rig to learn and get the "feel" of what is involved,--and you also
can have a lot of fun with a lowered powered transmitter on the air.

I suspect 75-100W is good enough for 40, but is it enough to be heard on 75?

[...] it will be a lot easier to find parts for a lower powered rig.

No doubt.
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David, K3TUE
W1LSB
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« Reply #12 on: October 06, 2005, 09:28:10 AM »

In his recent post, David, K3TUE said:
"This transmitter (as well as others in the Globe lone) strikes me as not only powerful and rugged, but also seems relatively simple and easy to understand in design.  Despite all of this, should I assume it is not a good one to start off with?  Or is Jim's comment about homebrewing one as good advice as any for a first Plate Modulated transmitter.

Maybe I'm just thinking too big."

Well David, it's big, but not complicated.  The Globe King is about as simple as it gets from a circuit point of view.  True to form, all WRL transmitters suffer from short cuts in the power supply and tank circuit areas, and this rig is no exception.  I've spent most of my career in RF systems for TV broadcast, so I tend to be over cricital when it comes to good design practice.  Truth is, Leo and his Globe rigs put a lot of people on the air at reasonble prices.  I can't really fault him for the short cuts; some of them were pretty ingenious, and, he had to stay in business.  My real goal here is to figure out how make it play better (in my own warped mind) using minimal invasive surgery and modern components.  I'm still benchmarking the original box, then I'll start.

The RF deck can be thought of as a Globe Scout with a one more stage of amplification; the 4-250.  Globe added time sequenced keying, which is a really nice touch for CW lovers.   The modulator is nothing special, but includes its own plate supply, which is a real plus even if the B+ is a bit wimpy.  In later models, the PS deck includes a 755 VFO, which is pretty doggone stable if the components are OK.  Having three separate chassis does make it a challenge physically, but electrically, it's no worse than a Valiant.  If you've ever torn into a DX-100, Valiant, B&W 5100, a 32V, or any of the standard AM rigs, you're ready for a Globe King or Globe Champ, in my opinion.

Home brew is an excellent way to learn, but finding time and parts can be a challenge.  The 100W level on 75M can be pretty good, that what a 32V puts out, and they seem to do OK. The key is fully modulating the carrier.  On 40M, I've had pretty good luck with my Globe Scout 680.
The 350W level is the next logical step.
Your mileage may vary. 

73, George - K1GXT


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K1MVP
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« Reply #13 on: October 06, 2005, 11:12:32 AM »

Being a "conservative",-- [...]
I would not consider building a 500 watt transmitter a good "first project".
I would think building a 75 to 100 watt plate modulated transmitter a much
better "first" rig to learn and get the "feel" of what is involved,--and you also
can have a lot of fun with a lowered powered transmitter on the air.

I suspect 75-100W is good enough for 40, but is it enough to be heard on 75?

[...] it will be a lot easier to find parts for a lower powered rig.

No doubt.


Hi Dave,
When I mentioned starting out on a "smaller level",--I assumed you meant
you wanted to homebrew a "first" rig.
If you are familiar with commercial rigs in general and used lower powered
transmitters,--I would agree that the transition to a Globe King would not
be that big a deal(case in point)--I had a GK back in the mid 60`s and
did not find it hard to use the rig after having numerous lower powered
rigs,(i.e.--a Ranger, a Viking 2, a DX-100, etc)

BUT when it comes to building a rig from "scratch",AND getting it to
work properly, with a "clean output" with no harmonics and spurious
emissions,--proper neutralization, etc, etc, then I think its a lot easier
to build a "low or moderate powered" rig to learn the "basics", as far
as layout, wiring techniques, oscillator--final amp, interaction etc, etc,
not to mention the problems that can arise in a "high powered" PA
with improper impedance matching, and neutralization.--cause when
things go wrong in a high powered rig,--they can  go wrong fast.

As far as getting on with 75 to 100 watts on 75,--Most Dx-100`s and
Viking II`s run about 100 watts out and you will hear lots of em on,--
You may not be a "big strapper", but who cares?--you will be heard
and still have a lot of enjoyment, AND in the process you will be on the
air and talking getting ideas from other guys who have built the "bigger"
rigs.--Just a few of my thoughts,

                                   73, Rene, K1MVP

P.S., I was on yesterday on 75 am with my FT-101,(barefoot) at about
       25 to 30 watts out and had a great QSO with guys in Maine and
       Conn,--and was Q5,--may not have pegged thier S meter, but so
       what?--still had a great QSO.
       I still think a homebrew pair of 6146`s would be a great HB xmtr. 
 
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KL7OF
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« Reply #14 on: October 07, 2005, 11:59:04 PM »

It looks like the HV power supply is choke input..(swinging choke?)  if you put a low Value (1/2 to 3 mfd) oil cap between the xfmr output and the choke it will increase the HV output of the supply.......simple and effective if the HV xfmr has the current capacity....I too like the looks of the GK 500..
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