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Message |
    
814
| | Posted on Sunday, October 21, 2001 - 6:11 pm: | 
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What are some easy mods I could do to this radio? I got it for cheap and I figured I'd play around with it. I want to tweak it and add more channels. What is this radio capable of? This version of the grant is about 6 years old. Version with the push buttons instead of the dials.
814 |
307
| | Posted on Tuesday, October 23, 2001 - 7:06 am: |
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Clarifier Modification
PRESIDENT GRANT AND MADISON
1)Cut d-52 and r-148.Find r-174 and solder a wire across the resistor.
2)Find the RED wire that comes off the clarifier control and cut it just before it connects to the PCB. Take that wire and solder it to GROUND on the PCB
3)Cut the orange wire just like the red wire but solder this wire to pin # 3 if IC-4 the
MB3756 ic regulator.
This should give you about 5 khz is slide on this radio. |
814
| | Posted on Tuesday, October 23, 2001 - 10:10 pm: |
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307: Thanks! That sounds simple enough. I'm going to fire up the soldering iron tomorrow. I cut D23 for modulation and people say the radio is really loud now. Using a Astatic 575-M6 with it. Haven't gotten any reports that I'm over modulating disgustingly or anything.
814 |
814
| | Posted on Tuesday, October 23, 2001 - 10:52 pm: |
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307: Maybe this is a stupid question. But where is GROUND on the PCB? I found everything else and I have the iron all heated up. But I have no idea where "GROUND" on the PCB is. |
Inspector
| | Posted on Friday, November 02, 2001 - 7:18 pm: |
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Generaly, the ground can easily be found as the LARGEST circuit trace covering the most area. This electrically connects things associated with a grounded item including the shield-cans of variable inductors and the "-" side of electrolytic capacitors. |
Highlander1588
| | Posted on Tuesday, December 25, 2001 - 8:20 am: |
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Here is the NPC-RC conversion for the GrantXL and the Cobra 148, first don`t remove tr24 it may be marked Q24 on some boards.This is the modulation choke and removing it will overmodulate the radio. Unsolder the center leg and pull it out of the board and put a 1K 1/4 W resistor in line with it.Cut R 131 to boost modulation. Then change C 174 to a 10 mFD Capacitor, remove R194 and set aside. Replace it with a 100 ohm 1/4 W resistor. Then remove R196 and put the resistor you took from R194 and put in its place. Then with a simple VOM remove the wire from TP7 and set the bias using VR8 for the final at 100 MA,then go to TP 8 using VR 9 and set driver bias to 50 MA. Then solder the feed wire going to TP7 to the cathode or banded side of D55 that will put 13.8 v`s to the final. Turn VR10 all the CCW before powering up radio, when on set VR10 so the carrier dead key is 2 watts.Peak the RF amp chain for max and you are there. |
Adshar64
| | Posted on Monday, June 09, 2003 - 6:18 am: |
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Here's the real McCoy:
1. Remove TR24 (dont clip r131)
Next a mod to the AN 612 balanced modulator circuit.
procedure is
a. Remove C 207 (47pf, Comes off AN612 pin 3 to ground)
b. Replace R206 270kohm (In series with vr4 sweeper leg to AN612 pin 1)with a 39K ohm resistor. NB I used a 56k in parallel.
Turn vr12 (amc) to minimum (This keeps the waveform symmetrical and helps modulation quality.
This deactivates the modulation limiters in all modes. Use the
front panel mic gain (aka dynamic) control to set the modulation
percentage.Usually 3 oclock position is best.
2. Add a solder bridge to the solder side of the board that
effectively jumpers out R196. This is a quick way of
replacing R196 with a jumper (reducing its value to zero
ohms).
This increases the range of VR10 (AM dead-key power) so that the
dead-key can be set to 1.5 to 2 watts later on.
3. Add a 10 uF 25 or higher volt electrolytic cap to these
points: the positive leg goes to the trace that connects to
pin 9 of the IC6 (the audio IC), and the negative leg goes
to the R194/D63/R228 junction.
This is the mod that compresses the negative modulation peaks and
allows the average power to increase based on the modulation
percentage (aka the NPC mod).
This is the end of the solder side work. The rest of the work is
done on the parts side of the board.
4. Set the driver bias to 50 mA. (Power up the radio, put it
in LSB or USB, set the mic gain at minimum, remove the wire
from test point 8, insert a milliamp meter in series between
the test point (which is positive) and the wire, key the mic,
and adjust VR9 until the meter reads 50 mA.)
5. Set the final bias to 100 mA. (Same instructions as in step
4 except the test point is test point 7, and the adjustment is
VR8).
On some of the newer radios the final bias can't be set higher than
about 50 mA. The reason is that the value of R179 has been increased
in order to decrease the effective range of VR8. To solve the
problem, replace R179 with a 500 to 1000 ohm resistor.
6. Once the final bias has been set, unplug the DC power cord,
put the final bias wire back on the test point, cut the final
bias wire 1/4 inch above the connector, strip and tin 1/8 inch
of the wire, tin the cathode (banded) leg of D55 (the reverse
polarity diode), and solder the wire to D55. This assumes the
test point connector is at the end of the wire that is furthest
from the final transistor. On some of the newer models the
test point connector is at the end of the wire closest to the
final transistor. On those models, completely unsolder the wire
at the end opposite the test point connector and solder it to
D55.
This is the mod that converts the RF final stage to linear in all
modes.
7. Power up the radio, put it in the AM mode, key the mic, and
set VR10 (AM dead-key power adjustment) for about 1.5 watts.
8. Tune the RF chain coils (L38 and L45 through L48) for maximum
peak (modulated) output power in the center of the band (that
would be Channel 19 on a stock radio and Channel 40 on one that
has the popular expanded frequency range of 26.815 to 28.045).
If you have a favorite channel that is more than 30 channels
from 19 or 40, do your tuning on that channel.
9. Double check the dead-key power. It should be around 2 watts.
If it is higher than 2 watts, use VR10 to cut it back to between
1.5 and 2 watts. Don't overdo it. Keep in mind that the carrier
(aka dead-key) power increases up to 10+ watts with modulation,
so there's absolutely no point in having the dead-key power any
higher than is required to reliably key an amplifier. Most amps
will key reliably with as little as 1/2 watt of dead-key power.
The following numbers are what you should expect. However, since
there is a lot of variation in CB test equipment setups, don't be
alarmed if you don't see these exact numbers. These numbers are
provided as a guideline to make sure you did the mods properly.
The dead-key wattage should be 1.5 to 2 watts. The maximum average
power should be 10 to 12 watts. And the maximum peak power should
be around 25 watts. |
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