Globe King 500 repair and restoration review

[KD6VXI]

I would rather just repair it.  It should key fine.. Its only a low power transmitter.

C

And so are every other transmitter you have, sans the Motorola one.

Grid Block Keying is how a LOT of the Johnson's end up, as it's easier on the relays and the rest of the iron.  Keying B+ requires quite a jolt.  If you have iron that is nominal (like I hear ALL iron in Globe products is), then you can quite literally, shock the crap outta it every time you key.  By going to grid block, there is no "slamming" the rectifiers and transformer into that 14uF cap.  It's charged all the time.

Or, another way to look at it is:  How many 1500 watt amplifiers do you own, or have you owned, that DIDN'T cut the tube off in RX?  How many have / do you own that DO?  Isn't the Globe King pretty much in the same Pout arena?

Admittedly, I don't know everything about the xmitter you're working on, but it is DEFINATELY not a relay problem, if others aren't having the issue.  BUT, fact remains.  Hot switching anything is bad mojo.

--Shane

[KD6VXI]

I would rather just repair it.  It should key fine.. Its only a low power transmitter.

C

Another way to look at it is:

Cutting B+ on TX requires switching 1500+ watts.

Cutting grid requires switching 30 watts???  BIG diff.

Also, if you are cutting the TX B+ on and off, you might be suffering from secondary inrush.  This was covered by the guys running LARGE xformers on the yahoo ham_amplifiers forum a few months back...  The SECONDARY inrush can be as large, or larger than the primary inrush.. IE, AFTER the step-start CLACKS and goes into "shorted resistor mode", the inrush current at THAT time can be as great, or greater than the inrush if left to attend to itself.

Again, I don't think that's your problem...  It would seem to me to be closer to something like a HV breakdown:  Something doesn't like the initial inrush of the TX.  Maybe a scope on the pins being switched could enlighten you....  As well as find a Hi-Pot tester to test your iron and caps.  Could be something like a feedthrough (not sure if they use those crappy things on that chassis or not) breaking down.  A lot of times, the inductive kick on key up and key down causes GREATLY increased B+...  Think the "anti spike" diode that you can series more diodes in on the AM CB chassis....  It's THERE to kill the inductive kick, and those radios aren't even switching the B+....  Does the Globe HAVE an anti-spike type diode on the mod line to the RF deck?

--Shane

[Steve - WB3HUZ]

BUT, fact remains.  Hot switching anything is bad mojo.

Not a fact at all. Probably every transmitter made from the 40's-60's used the switched primary method of powering up the HV when in the transmit mode (same arrangement at the Globe King). Such an arrangement is generally not a problem with a choke input supply. I'd be a little suspicious of the GK power supply since they used very minimal filter capacity. Increasing the capacitance significantly may cause a problem. You'd need to look at the inductor value to determine the inrush current. You may be able to simulate all this with SwitcherCad or some other Spice based software.

[Jim, W5JO]

I believe this is another case of not all mods are good mods.  If I were looking, the simple thing to try is put the old filter cap back in the PS and see what happens.  That will eliminate one potential problem and allow you to move to something else.

[ke7trp]

I am going to try the 866s.. I loose alot of power.. But if thats what it takes thats fine.

Clark

[KD6VXI]

I am going to try the 866s.. I loose alot of power.. But if thats what it takes thats fine.

Clark

What was the original cap value?  4 uF?  I think is what I read.

Going from 4 to 14 might not be that great of a thing:  That's nearly 4 times as much C, and can cause all kinds of problems.  You might want to try the cap first.

The rectifiers might make it work again, but I'd be willing to bet it's the hit the xformer takes every time you key the thing up.......  Going back to vac tube rectifiers might make the transition a lot better on the contacts, but doesn't address the real problem, and a problem that could cause those "expensive" rectifiers to also be blown / screw things up / etc.

Try a vac relay on the OUTPUT of the supply, rather than switching the primary?  If you must keep HV keying, that is, and you want to keep the high C.

You're welding contacts.  That means too much current.  What is causing the current draw?  The rectifiers don't, it's something else...  The rectifiers are softer than solid state, though, and can band-aid the fix.  The associated "BANG" also means high current.

I'd much rather keep the solid state rectifiers and lose a bit of C, especially since they give you more Pin to draw from.

--Shane

[ke7trp]

I think its a 12 uf.. But still.  The original was 3 or 4..  Thats not enough. I got big PEP gains with that big Power supply cap.  I really hate to take it out.

Let me try the rectifier tubes.. I will use it for a day like that.. Then if it works, Its fine. If not, We will step start it..  That should fix it right?

Clark

[Jim, W5JO]

Before you jump to conclusions do the math on ripple using the original cap and choke values.  If it is 5% or less then I don't see a problem.

Most of the hum on the GK series has to do with electrostatic shielding not lack of filtering.  I would have used a bit more C myself, but I believe you will find the original values are enough.

[ke7trp]

Jim. You are correct. I Had no hum before.. But this big cap is keeping the voltage up and really increased the peak output. I can remove it if it is infact, the problem.

C

[Jim, W5JO]

I would give it a try to see what happens Clark then plan from there.  Some mods simply do not work.  Some day ask John/K5PRO about published mods to the DX 100.  That is a real eye opener.

You really don't need 125% positive, 100 percent works fine and is smooth and easy on the ear.

[ke7trp]

Very true.. 

I got the 866s out.. Found two RCAs and Two GEs.   Put them in the TV7 tube checker for 5 minutes each..  GEs tested 65 each (40 minimum).  RCAs tested 45.   

Kinda neet to see the Tubes turn to chrome metal before your eyes.  I put the GEs in the Globe king.. I am going to bake them for a few hours before throwing the switch.. 

Clark

[Jim, W5JO]

You may be asking for trouble with those merucry vapor rectifiers.  Be careful.

[ke7trp]

After an hour of cooking.. I put it on tune and flipped the transmit switch.   BZZZZZ POW  blew the Primary fuse.  Put a new fuse in. Tried again.  Slight pop and another fuse.. 

Oh well.  Its not the rectifiers.. Time to yank the PS out and start over...

Clark

[KD6VXI]

After an hour of cooking.. I put it on tune and flipped the transmit switch.   BZZZZZ POW  blew the Primary fuse.  Put a new fuse in. Tried again.  Slight pop and another fuse.. 

Oh well.  Its not the rectifiers.. Time to yank the PS out and start over...

Clark

Time to check that filter cap, and any feedthrough caps.

You might also be checking the cap under low voltage (like any decent modern cap checker would be doing, since battery powered usually), and it might be breaking down under HV.

Replace that cap, I just have a bad feeling about it.  And, if it does fix it, and you still want the bigger cap in it, then a step start would fix it, but it would need to be robust, as you're not switching onto an unloaded power supply, you hit it full tilt.

I do NOT like HV keying.  Yes, nearly every transmitter made in the 40-60s had it, but has technology and our intelligence not moved beyond some things considered "good engineering practice" by 50-80 years ago principles?  YES, it does work, but it sure is HARD on your iron.  Commercial Mfg's could have cared less, they where ALWAYS ON.

--Shane

[Jim, W5JO]

Keying the primary of the HV transformer is not the problem.  It is the mods.  Put the original cap back in and work from there.  I hope you haven't shorted the choke winding or the winding to ground.

[ke7trp]

Pulling the PS now.. Going to fire it up on the table by itself.   No load.. Go from there..  I am going to study the PS again to make sure nothing on the high side is arcing.  Once keyed, I can talk for an hour... Full power. I think the iron is ok..

Clark

[Jim, W5JO]

I think the iron is ok..

Clark

Maybe

[ke7trp]

Power supply looks perfect.  No arcs anywhere...   

Set it up on the table. Locked the pets up.  Put a clamp on probe on HV output.  Plugged in the wall. Flipped Filaments on.

After about 5 minutes, I flipped the Transmit switch with a long pair of lineman pliers. Loud gutteral (deep) Clicking and the over head light DIMMED almost out.  Flipped it out of transmit.  Tried it again and it made the normal click and came up fine. No arc on relay.. I was looking right at it. 2000 volts or so.. 

Clicked it out of transmit,  Then on 5 times..  Normal click and 2000 volts. Then on the last time, I heard the Low thumping sound and the lights in the room dimmed out.  Fuse blew.

No idea what in the hell is causing that Thudding sound.. Must be the big cap?  No smoke, No smell.. No Arcs.  Sounds like a Thud thud thud... Then fuse blows.

I really hope its not the damn iron. 

Clark

[ke7trp]

I hope this is at least entertaining to someone.. LOL.

I put the Solid state diodes in..  2200 volts. No GLUG GLUG GLUG sound.. No dimming if lights. No sparks at contacts. Clicked it on and off 30 times.. 

So the big draw is happening somewhere else.. Mod deck or RF deck.. 

Clark

[Jim, W5JO]

Or the choke

[ke7trp]

Nope.. I put BIG resistors on the output of the PS.  Used ohms law to figure 250 mills.  Flipped the switch.. Current Draw.. Sounds normal.  Operated it for a few minutes into a load. No issues..  Resistors getting warm.  Volts Dropping to 1800.  Keyed it 35 times over and over. Not one spark or flash. 

This must be a flash over on the HV side of the mod or RF deck.  This PS is fully functional on the test bench. 


Clark

[KD6VXI]

This must be a flash over on the HV side of the mod or RF deck.  This PS is fully functional on the test bench. 

Clark

You mean, like HV Breakdown.

I thought in another post, you had pulled it out.  I took that to mean, you pulled it out, and only had primary VAC hooked up, nothing on the secondary (output of the supply, input to the Mod and B+ RF deck) hooked up, outside the cap / iron and rectifiers??

If so, and it still thumps, then it's in the cap(s) or the like.  If not, then ......  It's time to put the tech hat back on.

--Shane

[KD6VXI]

This must be a flash over on the HV side of the mod or RF deck.  This PS is fully functional on the test bench. 
Clark

Starting to resemble the Motorola rig, it sounds like...  MIGHT be a good thing.  Fix one, learn enough to get them BOTH goin!

Best of luck, I'm out for the night.  Vertical up tomorrow, HOPEFULLY.

--Shane

[ke7trp]

The PS was operated on the bench at 300 MA.  For minutes.. Switched 35 times.. No sparks.   To me, That means the PS is not the proplem.   This means that somwhere in the mod deck or the RF deck must be arcing over.. That would make a HUGE Draw on the Primary side relay and buzz the contacts.. Right?

C

[ke7trp]

Ok..  I found the left 866 socket BLACK as hell and covered in soot.  The right socket is clean and white. This must be the problem.  I am going to order two new sockets, Clean everything and install new.  Crossing fingers.


Clark