ka2pbo
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« on: June 05, 2013, 11:35:06 PM » |
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I noticed in some earlier Viking II there is an RFC ( L22) in series with the final screen dropping resistor but in mine there is a 56 ohm resistor. I have the earlier schematic with the choke but my schematic and rig have the 56 ohm resistor. Does anyone know why they switched to a resistor in later production? Just curious.
Thanks
Rick
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KA2DZT
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« Reply #1 on: June 06, 2013, 12:26:10 AM » |
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Probably costs, a small value resistor (like 56ohm) can work to break up parasitics as well as a small RFC. Maybe the 56ohm resistor is a wire wound type. If it is WW it will have a double width first color band (green band). Most all low value resistors (under 10 ohms) are WW. Are you sure it's not a 5.6ohm resistor?
Fred
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ka2pbo
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« Reply #2 on: June 06, 2013, 08:01:00 PM » |
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Thanks Fred,
So it is a parasitic suppressor .Thanks for the info . I dont remember seeing resistors used in other rigs I have played with. And yes it is 56 ohm 1 watt Carbon .
Thanks Again
Rick
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KA2DZT
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« Reply #3 on: June 06, 2013, 08:18:28 PM » |
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Rick,
That is my best guess what it would be there for. There are many members here that can tell you for sure why it's in the screen circuit. Many members have Viking II, just not me. I only have HB xmtrs.
I'm sure you"ll get more answers from members that know the rig inside out and backwards. so check back.
BTW, welcome to the forum.
Fred
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W9BHI
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« Reply #4 on: June 06, 2013, 09:22:06 PM » |
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My Valiant II has a 56 ohm resistor in the screen circuit also.
I replaced the original cause it was way off value.
Not sure why it's there either.
Don W9BHI
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KA2DZT
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« Reply #5 on: June 06, 2013, 10:22:15 PM » |
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Rick,
Only other thing that the 56 ohm resistor might be is a meter shunt, not really sure. Someone knows for sure.
Fred
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w4bfs
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« Reply #6 on: June 07, 2013, 02:55:57 AM » |
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parasite eater .... pa stage is unneutralized as well
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Beefus
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to see ourselves as others see us.
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pa0ast
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« Reply #7 on: June 07, 2013, 03:24:32 AM » |
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Parasitic stopper and cheap fuse, burns out if i square X R is higher then the max power handeling of the resistor. Speed of reacting ( burning )depends on the applied power. But if You have a flash over... its fast.
C74 is the neutradynisation capacitor.
Anton
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DMOD
AC0OB - A Place where Thermionic Emitters Rule!
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« Reply #8 on: June 07, 2013, 03:28:25 AM » |
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It appears to do two things:
With C38 and C45, it acts as a RF filter to keep RF from getting back into the clipper, and kills any high frequency audio artifacts, since the screen is modulated as well.
Phil - AC0OB
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Charlie Eppes: Dad would be so happy if we married a doctor. Don Eppes: Yeah, well, Dad would be happy if I married someone with a pulse. NUMB3RS  |
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ka2pbo
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« Reply #9 on: June 07, 2013, 09:24:24 PM » |
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Thanks for the info guys !! I am doing the Dean "KNX" screen mod as well as some other mods and and was wondering what it was for. I have been looking through some other rigs of the 100 watt class like the Apache and DX100 as well as some old handbooks and dont find the screen suppressors in them.
73
Rick
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wa3dsp
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« Reply #10 on: June 07, 2013, 11:54:55 PM » |
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Rick, I used the "KNX" mods in my Johnson Ranger when I did an extensive mod and it worked well. The screen is bypassed with a .001 and the mixing circuitry is mounted on a vertical aluminum plate with terminal strips near the final tube. See the photos and description here - http://www.crompton.com/hamradio/JohnsonRanger/RangerRestoration.html |
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ka2pbo
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« Reply #11 on: June 08, 2013, 09:41:01 AM » |
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Wow; you werent kidding....those are extensive mods ! Nice job !
Rick
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