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Message |
    
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 736
Registered: 9-2004
| | Posted on Wednesday, October 26, 2005 - 6:57 pm: | 
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i just finished installing a 10 turn pot in my 2000gtl.
i must say that i am VERY happy with the results.
the radio now slides about 17khz total.
this means i can now work all the even numbers (27.540etc...) and i no longer need a 10khz jump switch or a 5khz switch.
the radio is also alot more stable as far as staying dead on freq.
the only problem, if it even is one, is that the radio slides 13khz down but only 3khz up.
is this normal?
i would like to increase the upward slide to about 6 or 7 khz without giving up any downward slide.
can i do this by adding a choke to the varactor?
am i trying to get too much slide and creating instability?
never used to be a fan of the clarifier mods, but i think that was mostly because i didnt have the right test equipment to do them right. (i do now!)
so, any advice from the clarifier know-it-all's out there?
i am powering the clarifier from pin 1 of the MB3756 voltage regulator at the moment.
i do not like this and would rather run a regulated line from the mains. i just need to buy some parts first.
does anyone have a circuit they have already used for this purpose with success?
thanks for any help,
matt |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 859
Registered: 6-2004
| | Posted on Wednesday, October 26, 2005 - 7:53 pm: |
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Yes, it's pretty much normal and most folks like it that way to recover the "A" frequencies.
What have you done to get it to slide that far already? Usually that's about as far as you can go without losing stability. You're looking for about 25 KHz of slide and that's a lot - I don't know anyone who's ever had one with a range that wide.
I don't know what another couple of volts would do for range, but I suppose you could source a higher voltage than the one you're using now. You'd have to make very sure that it's still very stable when the radio is at full output.
Lots of folks with peaked out SSB rigs have warble because the power supply can't maintain a constant voltage on peaks - and most I've spoken to didn't have a clarifier with the range or yours. It's yet another reason not to peak out a base radio unless you power it from an external supply. |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 739
Registered: 9-2004
| | Posted on Wednesday, October 26, 2005 - 11:18 pm: |
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thanks so much for the reply.
i like the 13 khz down because it gives me back the channels i lose with the standard MB8719 PLL conversion (mine uses the 6 position switch)
the mod i did to my 2000gtl was: remove D52, D75, R44, R174, and D51.
replace R174 and D51 with jumpers.
run one lead form the 10 turn pot to the jumper where D51 was, another to PC ground, and the last one to pin 1 of IC 4 (mb3756).
i am always concerned about instability and having enough headroom, i have changed the main filter cap in the power supply to a 10,000uf, the big cap right in front of the audio IC was changed to a 3300uf, and the one near TR24 was changed to a 680uf. (i'll find the part #'s if you want, i just dont remember off hand)
i also replaced all the other elec. caps with new ones rated at 16v or higher.
i would like to power the clarifier off of the 3300uf cap, and like i said, i just need to buy a zener diode and a couple of caps and a 100ohm resistor first.
i have gotten good audio checks on SSB so far so i think im just going to be happy with the ammount of slide i have now.
im very embarrassed that i have never used a 10 turn pot before, as i am so impressed with the way this one is working.
thanks again hollowpoint,
matt
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Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 740
Registered: 9-2004
| | Posted on Wednesday, October 26, 2005 - 11:32 pm: |
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PS, i have thought about running it at 10 volts instead of 8.2 but i dont know what i might be doing down the line by doing this.
i run a 2 pill (dont you hate that term!?) with this radio, so i have the power turned down a bit.
on AM it keys at 2 watts and swings to 8-10 watts average, and 20 PEP. on SSB it does about 9 or 10 watts, so i hope the stability wont
be a big issue.
matt |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 862
Registered: 6-2004
| | Posted on Thursday, October 27, 2005 - 9:48 pm: |
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10 turn pots are pretty cool, but to be honest I always liked the dual pot setup that the Cobra 2000 has in stock form. You get as close as you can with the coarse and then fine tune it. Fast AND accurate - what more could you want? I've considered adding something like that to the radios I use because they don't come with one in stock form.
Lou Franklin suggests nothing more than 9.1 volts for clarifiers, but the reason he gives is voltage stability of the supply. With 20 watt peaks on your radio I'd guess that you're pushing the power supply to it's limit. All the capacitor will do is help to keep the voltage stable if there is enough current. Connect a DMM to the voltage tap you're using for the clarifier and watch it while you chat to see if the voltage drops. That's really the only way to tell if you have a problem. |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 748
Registered: 9-2004
| | Posted on Thursday, October 27, 2005 - 11:48 pm: |
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that's a good idea hollowpoint. i'll do it tonite.
it was a long decision to put this 10 turn pot in, as i had to enlarge the mounting hole. (i hate to do that, but im a good fabricator so i trust my skills)
i thought long and hard about it, and i finally came to the decision that i never used the coarse control. when clarifying someone on SSB, i only needed the fine tune control, so why not have a fine tune control that covers 15 or more khz.
the only problem now is finding a stock 2000gtl knob someplace. havent found anyone willing to part with any yet.
matt |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 866
Registered: 6-2004
| | Posted on Friday, October 28, 2005 - 9:39 pm: |
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Instead of having a stock knob, why not get a turns counter? I know you don't really need one with the frequency counter, but they just look cool.
Let us know what you find out about the voltage stability - I'm curious. |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 755
Registered: 9-2004
| | Posted on Saturday, October 29, 2005 - 11:03 pm: |
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havent had a chance to change the power source yet, but i have been talking on SSB and have asked if anyone hears a chirp or a warble, and the locals i trust have said they cant hear any difference from the way ive always sounded.
i am going to build my own regulator for it, and will probably run it at about 8.5 volts just for safety and stability.
(BTW, those 20 watt peaks are measured on a Rad Shak wattmeter, so who knows what it's really doing)
matt |
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