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Trouble with Johnson Ranger II crystal osc.




 
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Author Topic: Trouble with Johnson Ranger II crystal osc.  (Read 3496 times)
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Knightt150
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« on: September 15, 2014, 08:05:35 PM »

I use my ranger a lot (crystal controle), when using the crystal osc some crystals run others don't. I know all crystals are good and work great in the old ranger is there a common possible problem in the ranger II. I changed the 6CL6 crystal osc tube but to no avail.

John W9BFO
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Pete, WA2CWA
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« Reply #1 on: September 15, 2014, 09:43:22 PM »

All crystals are not created equal. Crystal aging (active crystal vs not so active(sluggish) vs I won't work here) is not uncommon. Also component tolerances (within spec) in the oscillator are important to excite a wide range of crystal conditions. You didn't mention it, but are you using fundamental or overtone crystals? What frequencies are talking about?
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Knightt150
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« Reply #2 on: September 15, 2014, 10:06:51 PM »

The problem first appeared with a 7160kc and 7159kc crystal, now my 7290kc crystal runs sometimes, very intermittent. The 7295kc never fails, these crystals came from Brian Carling FT 243 types. I don't think the crystals are at fault, and they are I hope fundamental crystals not overtone crystals.

John W9BFO
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Pete, WA2CWA
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« Reply #3 on: September 15, 2014, 10:32:42 PM »

Are these the ones where he retrofits those small computer grade crystals into a FT-243 package?
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« Reply #4 on: September 15, 2014, 11:22:20 PM »

John,

Just for grins & giggles: Take one of the crystals that doesn't work, put it into the crystal socket, CW mode and try loading the TX from scratch. BUT while keying the rig, try rotating that big VFO knob from one end to the other. See if the crystal starts working.

Don't know why, but my Junkston "500" can be picky with any crystal, even AF4K's. But there is a sweet spot on the VFO dial where the crystal will do its thing. Don't know why or could care less.......................

Craig,
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« Reply #5 on: September 16, 2014, 08:03:45 AM »

Craig,

The 500 behaves a little differently because it uses gang tuned circuit linked to the VFO, with the other Johnson rigs in that series exciter tuning has discrete controls.
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Rodger WQ9E
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« Reply #6 on: September 16, 2014, 10:37:52 AM »

hi John .... might try yer 6cl6 screen voltage ...if low chck screen resistor... ALL old carbon comp are suspects ... all Johnson rigs i've seen tend to have meter shunt problems ...73 ... John
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« Reply #7 on: September 16, 2014, 11:57:49 AM »

I can't remember but isn't the oscillator keyed? Could be the keying bias on the oscillator grid is just errant enough to prevent oscillation with some crystals.

73's

daniel W7NGA
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« Reply #8 on: September 16, 2014, 01:02:20 PM »

In the early Rangers, there was a 100k ohm grid-to-ground resistor in the crystal oscillator.

In the later Rangers (Ranger with grid block keying, and Ranger 2), the resistance from grid-to-ground on key-down is: 100k ohms + [(100k ohms + 47k ohms) in parallel with 330k ohms]= 202k ohms

In my experience, using my Ranger (early version), and using homebrew 6CL6 crystal oscillators of the same type as in the Ranger, and using AF4k crystals (small modern crystal inside of a FT-243 package)... you may find that changing to a lower total value of the resistors, in this chain, will make the crystals more likely to oscillate on key down.

I suggest that you reduce the value of R7 to 50k ohms, by tacking an additional 100k ohm resistor across the existing 100k ohm resistor that is connected to the grid of the 6CL6 at one end, and to the junction of the 100k ohm (R46) and the 330k ohm resistor (R44), at the other end. At the same time, you should reduce the value of R46 to 13 ohms by tacking a 15k ohm resistor across it.

This will reduce the total oscillator grid-to-ground resistance, on key down, to: 50k ohms + [(13k ohms + 47k ohms) in parallel with 330k ohms]= 101k ohms.

If that doesn't help enough, there is an additional change you can make... but try this first.


Stu
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Knightt150
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« Reply #9 on: September 16, 2014, 06:27:56 PM »

Thanks everyone for the help, I am very suspicious the crystal osc has some resistors that have changer value, those old carbon resistors tend to do that.

Thanks again John
W9BFO
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