Can you add course/fine clarifier to Grant-XL or Cobra 148GTL?

[ShakyMcQuiver]

Has anyone ever tried to add a course/fine potentiometer to a Grant-XL or Cobra 148GTL?

I used to have an old 148GTL-DX that had it and I absolutely loved it. My Cobra 2000 also has it.
And while I can always put a multi-turn precision pot in, they aren't practical in the mobile especially when you don't have a frequency counter!

I can get the pot for it (1K/20K) but wiring it in might be tricky. I've been studying the schematics, but if someone has already done this and could give some tips, I'd appreciate it!

Thanks,

 

[unit_399]

Just add the part where it says "add this circuit ." forget the optional switch.


I know that it says 858ssb, but it will work on the 148 as well.

- 399

 

[999]

Things are numbered differently in the 148. It doesn't look too difficult though.

This is a Cobra 2000 clarifier circuit.


This is the other end where it goes to ground. It ties in on either side of R425 (4.7K ohm).


This is the 148 circuit. Looks like change R175 to 2.2K ohm and tie in on the potentiometer side of R44 with the 1K potentiometer and you should be able to make it work.

 

[Enterprise312ok]

need to do this mod to my 138xlr, and my newer uniden wahington. Please post the location numbers for the 148 when you get it figured out.

 

[1iwilly]

found this on secret cb hope it helps book 12 page 20

 

[nomadradio]

Ah, 138XLR?

A tougher row to hoe than the post-1979 models.

A dual clarifier serves to allow a wider coverage range. Not a lot of reason to do it if the control covers less that 3 kHz end-to-end.

To stretch the range of the clarifier, you have to do it three times. Once to each of the three separate crystal oscillators in the PLL. One for AM receive, one for LSB, and one for USB. AM transmit frequency is controlled by one of the sideband trimmers. Forgot which one.

My experience trying this was that making each mode line up to center frequency at the same knob position was a struggle.

YMMV.

73

 

[Enterprise312ok]

Ah, 138XLR?

A tougher row to hoe than the post-1979 models.

A dual clarifier serves to allow a wider coverage range. Not a lot of reason to do it if the control covers less that 3 kHz end-to-end.

To stretch the range of the clarifier, you have to do it three times. Once to each of the three separate crystal oscillators in the PLL. One for AM receive, one for LSB, and one for USB. AM transmit frequency is controlled by one of the sideband trimmers. Forgot which one.

My experience trying this was that making each mode line up to center frequency at the same knob position was a struggle.

YMMV.

73

On my 138xlr the purpose of a dual clarifier would only be to make the control less touchey as I am not unlocking it.. I have a hard time gatting stations clarified while driving because the 138xlr clarifier is very sensitive.
Ditto on the clarifier center slot, my washington is unlocked and has different center position on each .mode.

 

[Low_Boy]

How about a 10 turn clarifier? In my opinion they work great and are pretty easy to do.

 

[unit_399]

A dual clarifier just allows the operator to more easily fine tune the receive to lock in a station. The schematic I posted is for the 858SSB chassis (138XLR, 139 XLR, Pres Washington, etc, etc, etc.) I adapted that mod from the dual clarifier on the 2000GTL. All that's required is the dual control (20K ohm/1K ohm) and 2 resistors. Can't get any simpler than that. Adding the circuit I posted allows an additional swing of a few hundred cycles to permit locking in a signal.
Try looking at the schematic of the Cobra 2000 clarifier to get a better understanding of how to hook it up. You guys are making a mountain out of a molehill.

- 399

 

[Enterprise312ok]

A dual clarifier just allows the operator to more easily fine tune the receive to lock in a station. The schematic I posted is for the 858SSB chassis (138XLR, 139 XLR,Pres Washington, etc, etc, etc.) I adapted that mod from the dual clarifier on the 2000GTL. All that's required is the dual control (20K ohm/1K ohm) and 2 resistors. Can't get any simpler than that. Adding the circuit I posted allows a swing of a few hundred cycles to permit locking in a signal.
Try looking at the schematic of the Cobra 2000 clarifier to get a better understanding of how to hook it up. You guys are making a mountain out of a molehill.

- 399

off topic but did you ever do the 858 dual final mod 399?

 

[unit_399]

off topic but did you ever do the 858 dual final mod 399?
Yes I did, but haven't gotten around to adding it to my site. Soon.

- 399

 

[Groundhog KSS-2012]

Hey all. What can I expect if I find the right person to "peak and tune", a grant xl. I have an old one that nothing has ever been do to but, I thought I might break it out again and see what kind of performance can be done to it without going over board. All info greatly appreciated.

 

[999]

Hey all. What can I expect if I find the right person to "peak and tune", a grant xl. I have an old one that nothing has ever been do to but, I thought I might break it out again and see what kind of performance can be done to it without going over board. All info greatly appreciated.

My suggestion is to not go overboard with the power from the radio. The finals have become increasingly hard to find. I think HG makes a replacement, but I don't know how close to drop in they are.
If you want more power just get an amp, you'll be much happier in the long run.

 

[Groundhog KSS-2012]

My suggestion is to no go overboard with the power from the radio. The finals have become increasingly hard to find. I thin HG makes a replacement, but I don't know how close to drop in they are.
If you want more power just get an amp, you'll be much happier in the long run.

Thanks. Appreciate it.

 

[ShakyMcQuiver]

How about a 10 turn clarifier? In my opinion they work great and are pretty easy to do.

Yes, the 10-turn does work well and I have one in my base station. The problem (imo) with a 10-turn in a mobile is that it can be difficult to find center frequency again. A frequency counter would certainly help, but I don't have one in my truck. And as you know, spinning the pot several times can get tedious.

I thought about a 3 or 5 turn pot. That might be ideal for a mobile precision pot, but they aren't easy to find, or at least I haven't had much luck. Thus the reason I thought of my old 148GTL-DX. The course/fine was awesome.

I'm old school like a lot of you. It's hard to get rid of our old rigs as they're too much fun to tinker with. I'm going to upgrade one of these days and get a true 10 meter export radio. I'm not sure which one yet as I've been out of the loop for years. I'm leaning towards a Galaxy though.