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Author Topic: Help" Lost Grid drive Globe Champion 300  (Read 7163 times)
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wb8uhz
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« on: March 28, 2009, 12:25:02 PM »

  Hello

 I have a WRL Globe Champion 300. While trying to fix a modulator bias problem I
lost all grid drive to the final tubes. I cannot get any grid drive output at all. I notice the OA2 is not even firing indicating its not getting any voltage. With a volt ohm meter I've checked the exciter switch and its seems to be funtioning. . I'm in the process now of checking all the associated resistors for any value changes. However if you have any suggestions please advise and much appreciated.
73 tim
wb8uhz
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ke7trp
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« Reply #1 on: March 30, 2009, 12:31:16 AM »

Feel free to email me on this. I have the schematics and manual for this transmitter. I use mine everyday. When this happend to me, It was the "Drive" pot.  That pot smoked. I replaced it and got the grid back. However, If you say you dont have the 0a2 working, You might want to check the Voltages as are listed in the chart and see what is missing. Its likely you lost one of the selenium rectifiers. Or you lost a relay contact. 

I just took a moment and said a prayer that your LV transformer has not died. 

Ok, I am back.

I would start by checking the voltages at the tubes and go from there.

Good luck!

Clark
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ke7trp
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« Reply #2 on: March 30, 2009, 12:32:07 AM »

Schematics:


* Globe Chump 300 005.jpg (308.1 KB, 1275x1755 - viewed 411 times.)

* Globe Chump 300.jpg (423.4 KB, 1275x1755 - viewed 448 times.)
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wb8uhz
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« Reply #3 on: March 30, 2009, 07:30:41 AM »

  Thanks very much. And thanks for the moment of silence for the LV xfmer. No still getting voltage to all tubes except the OA2.

73 tim
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W3NP
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« Reply #4 on: March 30, 2009, 07:50:13 AM »

  Thanks very much. And thanks for the moment of silence for the LV xfmer. No still getting voltage to all tubes except the OA2.
73 tim
wb8uhz

Check for defective R23 that feeds LV to the 0A2. Should have LV on one side and 150v on the other.
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wb8uhz
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« Reply #5 on: March 31, 2009, 09:41:54 AM »

  Thanks very much appreciated, anything else you may think of let me know. I have no voltage to the 0A2.

tim
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wb8uhz
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« Reply #6 on: March 31, 2009, 09:56:03 AM »

  I checked the voltage on R23. I get about 40 volts with the Champion only turned on. When on and turning on the exciter switch I get over 300 volts across R23.

Tim
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« Reply #7 on: March 31, 2009, 10:47:46 AM »

It looks like you are dropping the entire 300v across R23 (I am assuming that the LV is approx 300v based on the voltage indicated for the plate of the 2E26). That would mean a hard short on the 0A2 side of R23. Pull out the 2E26, check C29 for a short and check the drive pot. Is the 0A2 ok?

I would assume that R23 is getting very hot. Measure the voltage from each side of R23 to ground.

What is the power rating of that resistor?
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wb8uhz
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« Reply #8 on: March 31, 2009, 01:26:52 PM »

  OK

Thanks. I checked the drive pot with an volt ohm meter. The OA2 is good as I pulled a  working one from another rig. I need to get some .005 caps disk ceramic as I have none, maybe ( a long shot ) the local RS will have some. The resistor is a 5 watt carbon. Thank you very much once again.

73 tim
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W3NP
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« Reply #9 on: March 31, 2009, 01:38:15 PM »

Tim,

Check from the 0A2 side of R23 to ground with an ohmmeter. Based on your voltage reading across R23 you will probably find a few low resistance or no resistance to ground. Try that first.
If you do see a low resistance with the meter just start unhooking things until the short goes away. There are only a few parts that could cause it.
When you said you had 300v across R23 did you actually measure "across" the resistor and not from the supply side to ground? Does R23 get hot when you turn the exciter on?
Your trip to RS will probably be a waste of time as I don't believe they have any caps in the 500v range but maybe you will luck out. If the C29 is shorted, just unsolder or clip it out and briefly try to power it up. C29 is the screen bypass cap.
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wb8uhz
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« Reply #10 on: March 31, 2009, 06:03:34 PM »

  Dave

Thanks again. When I checked the voltage I went from one side of R23 to ground and then from the other side of R23 to ground. When the exciter switch was not turned on the voltage was about 40 volts. When the exciter switch was turned on the voltage was over 300volts on either side.

I did find some .0047 500V disk caps at RS.

For clarification, When I turn the Globe on there is no immediate short, it will idle but of course there is no grid current when turning on the exciter switch. When turning on the exciter switch there is no grid current but R23 will get warm and in time hot. This was the resistor (R23) that burned when I was transmitting a few days ago. I replaced it with the 5 watt 6800 ohm resistor as I did not have the exact value of 8200 ohms in the junk box,( I just checked and its now about 10,000 ohms, the heat must have changed the value. When first changed (R23) the rig had grid current, was transmitting but the bias was still to high on the 809 tubes, it should be about 50 mils but was closer to 100. I started checking the resistors in the fixed bias section which is where R23 is located with several other resistors. While testing I found one resistor out of tolerance and changed it, the bias however still read the same. Suddenly I noted while trying to test the Globe that I had lost grid current and that the OA2 tube does not even light up when the Exciter switch is turned on , which should occur.

Tim
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« Reply #11 on: March 31, 2009, 09:10:25 PM »

Well Tim, if you have the same voltage on both sides of R23 then it has no current flow through it - as though the 0A2 side is not connected to anything. In looking at the schematic the supply side of R23 is connected directly to the LV supply and it is marked 350V, so you should see whatever is present at the LV supply (junction of CH1 and C66). If that is the case and it appears to be, then there is either a problem with R23 (you said it went high in value), but probably not high enough to cause the problem or the 0A2 side is not making contact with the 0A2 tube pin, the 0A2 socket is bad or wiring is bad in that area. The drive pot R22 should drop the 150V or so which would be present on the 0A2 side of the pot (if the 0A2 was firing) and the wiper is like a voltage divider for the screen voltage. The schematic says 40v on the screen and that is what you said you saw with the exciter off.

Must be missing something simple or something caused by the troubleshooting you did on the modulator bias problem.

It does not appear to be a short or low resistance on the 0A2 side of R23, so C29 is probably ok. OH - your RS gets a 2 star rating for having those caps!!

When you said 300 volts across R23, I assumed you had one probe on one side and the other on the other side.

Good luck Tim,

Dave
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wb8uhz
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« Reply #12 on: March 31, 2009, 09:39:49 PM »

  Dave

On the side of R23 phiscally closest to the 0A2, on that side to chassis ground I get 300 voltes with the exciter switch turned on. On the other side of R23 to chasis ground the volt ohm meter will read backwards.

Tim
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« Reply #13 on: April 01, 2009, 08:06:22 AM »

Tim
Meter reads backwards??  I assume the black lead is connected to chassis ground for both readings??
I would carefully check your wiring in that R23 area that you were working in before this all happened?
The initial failure of R23 may have just been age or undersize and not related to your latest problem at all.
I have found that when I work on a rig and then something strange begins to happen, it is usually a result of something I did wrong.

You could try disconnecting the drive pot from the 0A2 and substitute a fixed resistor of same size (ohms and watts). If you do this and all is as it should be, your regulator tube should fire and you will see 150 volts on the side of R23 connected to the 0A2.

Make sure you install correct value of R23.

Dave
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wb8uhz
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« Reply #14 on: April 01, 2009, 08:19:51 AM »

  Yes I think you're right. I wonder If I have lost B= to the vfo, although I have been trying also using a crystal with the VFO switch in the VFO position.

Thanks for all your help.

Tim
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