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Old uniden Grant PC409ac board

Frylock508

Member
Jul 25, 2011
28
1
11
MB8719 In the Grant

After changing the cap in this radio I was wondering if it is possible to expand the frequencys even more than I have. There was a tech one time who did a mod on a 142gtl that went from 26.515-28.045. I know the Grant has the same chip but all i see for the standard mod is 26.815-28.045. This guy did this mod flawlessly. Anyone know how this mod was achieved? I've seen kits that go down that far but don't go up further than 27.855 of close to that. Any ideas?
Also am thinking of adding a roger beep and using one of the existing switches. Difficulty level of this?
 

F0GIQ

W9WDX Amateur Radio Club Member
Mar 27, 2013
3
0
11
Hi, all
Sorry for my bad English
I have a problem on TX for my Grant PC 409 AC, the led is always green no TX, what is the TR responsive of this, please
All electrolytics 10 Volts changed :)
Good day
Michel
 

Robb

Yup
Dec 18, 2008
11,433
3,569
323
Silicon Valley CA, Storm Lake IA
Check the vco voltage ch1-40 and see if the voltage is right.
See if freq is locked on tp1 ch1-40 .
If unlocked; no tx.

Also check keying transistor TR35, IC4, and D43.
 

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Ford1963

New Member
Feb 20, 2018
4
0
1
58
I have a uniden grant. and it only tunes right with these frequencies. The board I’d pc409ac and won’t tune up any other way. There’s a bit of different in the one that was sent before in the Boralos post. upload_2019-2-1_21-11-2.jpeg
 

sonoma

Sr. Member
Sep 14, 2005
2,105
935
123
oklahoma
check the voltage in step 1 in the vco section and see if the radio is locked on freq. if this is not right the light will not change.
also the age of the unit you may have a bad cap causing this. the radio may need to be recapped before you can proceed on.
 

NZ8N

Sr. Member
Dec 25, 2017
435
685
103
58
you can speed up the AMC attack time by replacing C109 with a 3.3uF cap.

There is no need to cut R whatever, or changing C109 to a lower value, leave them alone, C109 is the sample and hold part of the where the AMC and ALC both come together. The attack time is fine, it is the release time that you want to shorten up. I paralleled C109 with a 22k resistor on the solder side of the board, this shortens the release time of the cap, then readjust the AMC and ALC, this turns it into a syllabic speech processor, instead of the AMC and ALC clamping on the whole word, it now releases after each syllable. On SSB, instead of a triangular sideways Christmas tree pattern, it fattens it up so most of the syllables (humps on the scope) are at or near the rails. All curves, no flat tops on SSB, no overmod pinch points in AM. My former shop in Ohio still uses this method, I taught him well.
In a Galaxy style board like a DX99V, I used a 10k in the same area, across C133 before TR34, the PNP transistor where the AMC and ALC come together.
In a Ranger RCI-2950 (old non-DX), 10k across C147 before Q31. 2970, I used a 22k, as 10k was too short of a sample time. Ranger RCI-2950DX, C168, Q41.
 
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loosecannon

Sr. Member
Mar 9, 2006
4,200
3,603
273
well that's neat as all get out!

thanks for the tip.

i stopped doing the C109 thing quite a while back, as i never really saw a noticeable difference.

what kinds of magic have you tried with the receivers of this chassis?
LC
 

Ford1963

New Member
Feb 20, 2018
4
0
1
58
Hi guys this may be a bit of the subject your all on. I hope you don’t mind me asking. But does anyone no what Pf C121 is. it’s a small ceramic capacitor. It’s the one next to the veractor diode. I looked on the schematic but the value is not readable. Thanks every one
 

Ford1963

New Member
Feb 20, 2018
4
0
1
58
Hi guys this may be a bit of the subject your all on. I hope you don’t mind me asking. But does anyone no what Pf C121 is. it’s a small ceramic capacitor. It’s the one next to the veractor diode. I looked on the schematic but the value is not readable. Thanks every one[/QUOTE
 

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