I have realigned the tripler, and I can get lsb and am centered up, but the ferrite core bottoms out in the tuning can before I can get usb centered up. I still can’t get the clairifier to track the right way no matter how I wire it... it works just fine, it’s just that the way it tracks is counter intuitive.
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Cobra 148 gtl 10 turn clairifier
- Thread starter red97k1500
- Start date
red97k1500,
Most times when the clarifier is "unlocked" it takes VR5 out of the "alignment process"(used for AM transmit frequency). I'm not sure that it takes CT2 out of the picture, but CT2 should be used to get your USB on frequency.
Have you tried to get the USB closer to "on frequency" with CT2?
73's
David
Most times when the clarifier is "unlocked" it takes VR5 out of the "alignment process"(used for AM transmit frequency). I'm not sure that it takes CT2 out of the picture, but CT2 should be used to get your USB on frequency.
Have you tried to get the USB closer to "on frequency" with CT2?
73's
David
there are two main styles of these 10 turn pots.
one of them has a pinout like this:
in this style, terminal 1 is the wiper (center terminal on the stock pot) and goes to R174.
terminal 2 goes to the constant 8v. usually pin 1 of the MB3756 regulator
terminal 3 goes to R175 and then to ground.
many mods will tell you to go directly to ground, but that is dangerous and there should always be some resistance in the line even if it's just 100 ohms.
when you can't get the clarifier to line up after the mod, its because it's been thrown off balance by jumpering R174 and removing R44.
you can't change the voltage coming in, so that means the max value is pretty much set.
to move the 'middle' around, so you can align the radio, you need to experiment with different varactor diodes.
MV201, NTE612, and NTE613 are good places to start.
you can also add some inductance in series with the varactor. don't go over about 5.6uH.
i cant remember whether this lowers or raises the center freq though.
changing the value of R175 to a lower value will allow some more downward slide, but again, don't go too low because you are basically shorting 8v to ground when the clarifier is turned all the way down.
the second style is like this:
in this style, terminal 1 goes to R175 (ground side)
terminal 2 goes to R174 (wiper)
terminal 3 goes to the 8v (pin 1 MB3756)
hope this helps
LC
one of them has a pinout like this:
in this style, terminal 1 is the wiper (center terminal on the stock pot) and goes to R174.
terminal 2 goes to the constant 8v. usually pin 1 of the MB3756 regulator
terminal 3 goes to R175 and then to ground.
many mods will tell you to go directly to ground, but that is dangerous and there should always be some resistance in the line even if it's just 100 ohms.
when you can't get the clarifier to line up after the mod, its because it's been thrown off balance by jumpering R174 and removing R44.
you can't change the voltage coming in, so that means the max value is pretty much set.
to move the 'middle' around, so you can align the radio, you need to experiment with different varactor diodes.
MV201, NTE612, and NTE613 are good places to start.
you can also add some inductance in series with the varactor. don't go over about 5.6uH.
i cant remember whether this lowers or raises the center freq though.
changing the value of R175 to a lower value will allow some more downward slide, but again, don't go too low because you are basically shorting 8v to ground when the clarifier is turned all the way down.
the second style is like this:
in this style, terminal 1 goes to R175 (ground side)
terminal 2 goes to R174 (wiper)
terminal 3 goes to the 8v (pin 1 MB3756)
hope this helps
LC
Thanks for the info LC. I was not aware of the 1st type you listed above.
Since I had just removed this failed pot from a Grant XL, I assumed this was standard. It is indeed a Bourns 3590S-2-103L. I guess you can't take anything for granted!
Explains why red97k1500 is having trouble.
73's
David
Since I had just removed this failed pot from a Grant XL, I assumed this was standard. It is indeed a Bourns 3590S-2-103L. I guess you can't take anything for granted!
Explains why red97k1500 is having trouble.
73's
David
Hurry up and work out the details, I got projects sitting here, hahaha.
This is all my personal, recently acquired, stash.
This is all my personal, recently acquired, stash.
So with that in mind, If your 10 turn looks like the first example that LC has pictured (the terminals are Not in a straight line), 1 = Blue, 2 = Orange, and 3 = Green.
If your 10 turn looks like picture #2 in LC's post (has all 3 terminals in a row), 1 = Green, 2 = Blue, and 3 = Orange
When it is hooked up correctly, the voltage on the blue wire should increase when you turn the shaft clockwise.
Oh and BTW, I realize it is too late now in this case, but you never, ever, ever have to re-align a radio when you unlock the clarifier. Period.
As long as the radio was "on frequency" when you started and as long as the new constant voltage is equal to or greater than the original TX voltage, you are good to go.
1. If you are going to use the original clarifier, where the knob is keyed to the shaft and can only be centered in one position, you simply add a VR (variable resistor) in series with the wiper. The new voltage is going to be higher than the old TX only voltage. Simply put the clarifier knob in the "centered" position, start at zero resistance and adjust the VR to increase resistance thus lowering the voltage. I would zero beat it on SSB into a trusted radio and you are good to go. I like the precision 10 turn VR's for this. A 5K should be suitable for this in most cases.
2. If you are going to replace the stock clarifier with a 10 turn model, it is even easier. Make sure the resistance value matches the original clarifier, wire it up correctly, and then just turn the shaft and dial it in. Again I would zero beat it on SSB into a trusted radio. When you are satisfied that you are "on freq.", hold the shaft still and put the knob on with the line/mark at 12:00 oclock. Done.
The difference between a locked clarifier and an unlocked one is voltage - constant vs. switched. It has nothing to do with the "tune" or alignment.
As long as the radio was "on frequency" when you started and as long as the new constant voltage is equal to or greater than the original TX voltage, you are good to go.
1. If you are going to use the original clarifier, where the knob is keyed to the shaft and can only be centered in one position, you simply add a VR (variable resistor) in series with the wiper. The new voltage is going to be higher than the old TX only voltage. Simply put the clarifier knob in the "centered" position, start at zero resistance and adjust the VR to increase resistance thus lowering the voltage. I would zero beat it on SSB into a trusted radio and you are good to go. I like the precision 10 turn VR's for this. A 5K should be suitable for this in most cases.
2. If you are going to replace the stock clarifier with a 10 turn model, it is even easier. Make sure the resistance value matches the original clarifier, wire it up correctly, and then just turn the shaft and dial it in. Again I would zero beat it on SSB into a trusted radio. When you are satisfied that you are "on freq.", hold the shaft still and put the knob on with the line/mark at 12:00 oclock. Done.
The difference between a locked clarifier and an unlocked one is voltage - constant vs. switched. It has nothing to do with the "tune" or alignment.
just to add to the good info Dmans has posted, it's when you upset that voltage divider made up of R44 and R174 that the center of the clarifier range gets shifted.
LC
LC
Dr_DX,
I've never been fortunate enough to open the cover on a radio that 1900 hands haven't already been in to. Thus they are never on frequency from the start and every resistor in the clarifier chain has been removed and jumpered out.
I guess that's what keeps it interesting!
73's
David
The easiest way I found to determine the center or wiper on some of these pots is with an ohm meter. While reading the pot outside the circuit, the two end terminals on your pot will always read approximately 20k, regardless of any adjustment. Simply try different terminal combinations with your ohm meter until that’s achieved. Those two are the ones you need to swap in the circuit for it to work in the opposite direction. The leftover terminal that's not connected to your ohm meter is your center wiper.
Thank you everyone, this info has been very helpful... and more importantly, I think it will be helpful to people in the future that come across it. This way hopefully, if someone wants to try out a ten turn. now they can do it themselves, with just a few dollars in parts.
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