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Author Topic: I picked up a Globe King 500 missing HV transformer Have a UTC S-49  (Read 5909 times)
K1YTG
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Posts: 210




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« on: August 06, 2012, 11:55:00 AM »

I was suprised by a Globe King 500 at a flea market  (non-ham,  just general antiques)  Seller was not sure what it was but had looked on the internet and saw $1200 price somewhere.  Being rough and missing HV transformer I offered him $200 and it came home with me.

I don't have any transformer that will fit in that space.  They are all too big.  The closest I have to the specs is the UTC s-49.  The voltage is right at 2100 - 0 - 2100   but the rating is 300 ma.  400 ma would be better.
What are the chances of finding something that is a better match and fit?

Can I just run the transmitter at or below 300 ma.  In the manual it says not to modulate it unless fully loaded. Why is that?   What is wrong with running it with less loading?  Is that not taking it easier on all the components and building up less heat and making them last longer?
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KA5N
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« Reply #1 on: August 07, 2012, 10:10:25 AM »

Can I just run the transmitter at or below 300 ma.  In the manual it says not to modulate it unless fully loaded. Why is that?   What is wrong with running it with less loading?  Is that not taking it easier on all the components and building up less heat and making them last longer?

Are you sure you understand what "fully loaded"  means?   It means matching the load
presented to the antenna correctly to the finals.  You do this with the old dip and load
routine.  When you have the finals properly loaded you will have LESS capacity set up by
the load capacitor. 
Since you have lower voltage you will have lower current draw.  Should still work fine just
won't put out as much power.  If it is fully loaded all will be well.

Allen KA5N
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K1YTG
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Posts: 210




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« Reply #2 on: August 07, 2012, 11:44:17 AM »

The manual says advance the antenna coupling ( and dip the tuning ) to obtain 320 ma final current.  I thought this is what they refer to as full loading.
If I put in a lower capacity transformer I will not feel safe loading up to 320 ma.  So what I meant to ask is if loading and dipping up to 275 ma will be OK.  You suggest that it will be fine, just with a lower output.
This still leaves me puzzled as to why on this transmitter and others, they  have a target to shoot for and want you to run the transmitter at that level.  A lower level (with resonance) would be easier on all the components.
Actually the warning in the manual is  "do not modulate unless the final amplifier is fully loaded."
No warning on running lower power in CW. 
Is there a mismatch at the modulation transformer at other than the specified loading?
Norm
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KA5N
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« Reply #3 on: August 07, 2012, 02:20:11 PM »

I suggest you go to WWW.W8JI.com/loading_tube_amps.htm-

Tom Rauch is much more into most aspects of amp design and use.
If you read this write-up and some of the others he has on line you
will get a better idea of what is going on. 
Radio Engineering by Terman is another good work if you can find it.

Good Luck
Allen KA5N
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KQ6Q
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« Reply #4 on: August 07, 2012, 08:04:03 PM »

the caution about not modulating unless fully loaded is because the modulator de issigned to modulate the design final plate current -
if you do try running the transmitter this way, you'll need to be VERY careful not to over-modulate. You'd be safe running CW, but that's not what you bought the radio for, I think!
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G3RZP
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« Reply #5 on: August 08, 2012, 11:02:11 AM »

If you don't take long winded overs (say more than 5 to 10 minutes), you could generally get away with running over the current limit. If you go in for lengthy transmissions though - forget it!
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W5JO
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Posts: 59




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« Reply #6 on: August 08, 2012, 12:43:40 PM »

That modulator and RF deck was designed around 1800 volts at the plate of the final.  If you run less power then the tank circuit sees a different load impedance and your harmonic suppression will suffer.  Also the modulaton transformer wants to see the impedance presented to the secondary with 1800 volts at the rated current in your manual.  Anything different changes that ratio and your audio may suffer.  Most changes like this are not good and affect the transmitter in negative ways.  IIRC the Q of that tank circuit is 10 which is bare mimimum.  Any change to it could cause that figure to fall dramatically
« Last Edit: August 08, 2012, 12:46:38 PM by W5JO » Logged
K8AXW
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Posts: 3963




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« Reply #7 on: August 08, 2012, 07:28:41 PM »

The Globe King transmitters are plate modulated transmitters with an input power of 500 watts or so.

The modulator will supply 250 watts of audio to modulate the transmitter 100%.  If you run the transmitter at a lower power level and still use the 250 watts of audio you will overmodulate horribly.  As an owner of the Globe King 400b, I don't recall ever being able to adjust the audio modulation down and I don't recall the 500b being able to do that either.

This is why you run the thing at full bore.  On CW, there isn't any problem running at lower power.
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K1YTG
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Posts: 210




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« Reply #8 on: August 08, 2012, 11:21:49 PM »

Any ideas on where to find a power transformer for the globe king 500?  As I have looked at it I have wondered how such a small power transformer can get the job done.  Every other power transformer I have in this voltage and current range is much larger.  The one in the BC-610 is 3 times the size.  The BC-610 modulation transformer is also much larger than the globe king.  The tuning cap in the final is also a light weight with 1/3 the spacing of the one in the BC-610.  The whole transmitter looks like it is made of parts that would strain under the load when operated.  But the globe king does have a good reputation so I hope it will work when I get a HV transformer for it.
Thanks, Norm
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W9GB
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Posts: 2656




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« Reply #9 on: August 09, 2012, 06:04:21 AM »

Norm --

Peter Dahl (SK) had an extensive database for building commercial, professional, and amateur radio HV transformers and chokes.  Before he passed away, this database was sold to Jeff Weinberg at Harbach Electronics.

Here is the Harbach/Peter Dahl database for the WRL Globe King transmitters.
Products are listed for the Globe King 500A, 500B, 500C
http://www.harbachelectronics.com/_mgxftp/pwdamateur/PWDAMATEURG.PDF

GLOBE KING 500B PLATE TRANSFORMER
1800 VDC @ 400 MA CCS FWB CHOKE INPUT CORE) EI-175 X 5 STYLE #) 05 E-I LAMINATED CORE
PR) 115 VAC 60 HZ 1 PH
S1) 4000 VCT @ 400MA ICAS (FWCT)
DM) HT = 5.250 WT = 4.375 DT = 8.000 MD = 6.125 MW = 3.500 WEIGHT) 31 LBS

Harbach Electronics, LLC
468 County Road 620
Polk, OH  44866-9711
Phone:  (419) 945-2359
FAX:  (419) 945-2359
Email: info@harbachelectronics.com
===
Globe King 500 Restoration -- by WA5CMI (over 100 hours of labor)
This was featured in Electric Radio magazine in late 1990s
http://www.qsl.net/wa5cmi/gk500.htm

http://www.qsl.net/wa5cmi/summary.htm

A challenging restoration
http://www.qsl.net/wa5cmi/ps_pix_b.htm
===
Globe King 500C Restoration -- KE7TRP
http://www.arizona-am.net/PHOENIX/KE7TRP/globe_king.html

===
Globe King 500 Power Supply Deck Rebuild / Restoration -- W0YVA
http://www.isquare.com/personal_pages/globeking500-psdeck.htm#top

« Last Edit: August 09, 2012, 06:20:58 AM by W9GB » Logged
K1YTG
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Posts: 210




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« Reply #10 on: August 09, 2012, 10:16:14 AM »

Great list of resources.  Thanks for taking the time to compile that.  I will see if Harbach is continuing to make transformers. 
I am still trying to figure out a way to use the UTC S-49.  At least I can use it outboard to check out the rest.
This is going to be a long project.   So far is has taken days just to clean it out and get it it looking halfway decent.  The mice ate into some of the paper in the transformers but I think the windings look fine.   
I am nor sure if it uses 5514 or 811A  in the modulator.  I will check to see what the filament voltage is.
Norm
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K1YTG
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Posts: 210




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« Reply #11 on: August 09, 2012, 06:02:40 PM »

I have located a HV transformer that will fit in the space on the power supply chassis.  It has 220 and 240 volt taps on the primary and it is listed as 1680 volts on the secondary at 400 ma  I think it came out of a commercial unit and is rated for constant service.   I am figuring that if I put 240 in on the 220 tap that will up the secondary to around 1800. 
It was used on a more modern amp with 2 3-500Z.    It produced RF but not for radio transmission.  It had a bridge rectifier so there is no center tap. 
This might work out as a permanent replacement.  Or perhaps I will get a transformer that meets the original specs, if I am lucky enough to find one.
The 75 ohm drop down resistor for the HV still reads correctly,  But is has been badly overheated.  This transmitter has had some abuse, perhaps.
Norm
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W5JO
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Posts: 59




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« Reply #12 on: August 10, 2012, 05:00:36 PM »

Return the RF to design specifications and you then can determine if it needs other help.  Return the modulation deck to original for the same reason.  I have a 500A that will modulate properly up to 100% positive and about 95% negative.  That is really all you want, especailly in the negative. 

If you need 5514s then let me know, I have a boat load.  Replacing plate and modulation transformers is an expensive process.  When you finish you will have more invested in the transmitter than the monetary value, but it is a good piece of equipment.  Not only that, if you have good transformers, chokes and such it is easy to repair if necessary.

The transformer you have found that uses 220-240 volt will require you carefully balance the rest of the load on the primary.  The rest of the transformers requires 115 volts to run the bias, filament, low plate voltage and relays.  There are some 500s out there that has the transformers that you can find.  Look at other venues and ask around.
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W2WDX
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Posts: 188




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« Reply #13 on: August 10, 2012, 06:36:46 PM »

The information given above is correct for the most part. The only thing I will add is to make sure that whatever transformer you use that the resulting voltage is correct at the plates of the PA. This is crucial for the correct impedance for the secondary of the modulator and proper for modulation levels. It also effects linearity of the modulator, since what is presented at the secondary of the mod transformer effects the primary as well, which effects what is presented to the modulator tubes plates.

The current draw of the original plate transformer as listed for the Globe King 500 is rated at ICAS, and not CCS. Therefore any CCS rated transformer near the ICAS rating (within 80%) is quite more than enough. It is more important to make sure your voltages throughout the radio are consistent with the original design parameters, if your transformer supplies sufficient current.
« Last Edit: August 10, 2012, 06:42:06 PM by W2WDX » Logged

K1YTG
Member

Posts: 210




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« Reply #14 on: August 10, 2012, 06:55:49 PM »

I am getting a lot of good information here and I thank all of you for it.  It this point I think I have enough parts to proceed, even though I will keep looking for a proper HV transformer for the 500.  With the transformer I have I can get it close and perhaps put it on the air.
I do need the 5514 tubes, I have not checked the filament voltage but the chassis has 5514 written on it. 
I still have a lot of cleaning to do.  I will be testing out the electrolytic caps .  They probably need replacing.  Do you suggest I go a lot higher in value?  Norm
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