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Author Topic: Johnson Ranger - low screen voltage on 6146  (Read 838 times)
N7TM
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Posts: 10




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« on: January 12, 2019, 08:40:14 AM »

I've got a Johnson Ranger I was hoping to get working for tomorrow's Classic Exchange. The problem I'm having is little-to-no output. I can hear the VFO in the receiver. I can hear audio in the receiver in phone mode. I've tracked down the problem to the screen voltage on the 6146, which is also the plate of the 6AQ5. On transmit, the manual says it should be 190v. I read 16v. It looks like that voltage is supplied from the big 30k R15. On transmit, the 6146 plate side of R15 reads 588v, but the other side, which supplies the 6AQ5 plate and 6146 screen reads 16v. Any ideas why?

Here are some other voltage measurements. R35 is the big tapped resistor on the plate supply that feeds the screen of the 6AQ5. On transmit, the tap reads 183v. The plate supply reads 592v on transmit.
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KB2WIG
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« Reply #1 on: January 12, 2019, 11:02:20 AM »



You may find the following link useful. Dr. Latta does a nick job breaking down the various ckts. of the Ranger. I wish this resource was available when I started playing around with the naughty Rangers.

http://faculty.frostburg.edu/phys/latta/ee/ranger/schematic/rangerschematic.html

Good luck,

klc

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K1YTG
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Posts: 493




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« Reply #2 on: January 12, 2019, 03:01:51 PM »

This screen voltage is controlled by the clamper tube.  And also the operate switch.  By connecting a circuit to ground the screen voltage is reduced to protect the 6146.
If you pull out the clamper tube and the voltage on the screen comes up then you will know that the clamper tube is the cause.
But make sure you have drive to the 6146 as the protection for low drive will be removed.
Norm
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KE0ZU
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« Reply #3 on: January 12, 2019, 06:54:34 PM »

Have you verified you have sufficient drive to the final and 6AQ5?   If drive is low or absent, the 6AQ5 is doing it's job, shunting the final's B+ to ground.

Further in "Zero" there is no drive to the final.

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Regards, Mike
https://mikeharrison.smugmug.com/
Pics and bold print are usually links.
N7TM
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Posts: 10




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« Reply #4 on: January 12, 2019, 07:11:47 PM »

Thanks for the Dr. Latta link. It's been really interesting reading through each section of the circuit. The 6AQ5 is apparently doing it's job. I found the transmitter works fine on 20, 15, and 10 and the keydown plate voltage of the 6AQ5 is between 100-150v, on those bands. Now I've got to figure out why there's insufficient drive on 160, 80, and 40, although I can hear the VFO in my receiver.
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N7TM
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« Reply #5 on: January 18, 2019, 08:16:09 PM »

I found and fixed the problem. R8 had gone from 68k to 95k and R9 was open on the buffer amplifier. After replacing both resistors, the Ranger now works on all bands at full output.
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