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cobra 2000gtl mods

hotrod

Well-Known Member
Feb 16, 2007
2,514
376
93
n.w pennsylvania
need some vrs for this radio
ssb power/alc
am power/dk
amc/modulation
ive found on one site modulation is vr10
but on another i dont remember which one now been a few years but said vr7 was modulation.i thought vr7 was modulation meter.like i said its been several years
i tried cbtricks.com but nothing
 

Im not a tech but I would not cut R131

I found VR12 as modulation

1 AM signal meter
2 SSB " "
3 squelch
4 carrier balance
5 Xmit Freq
6 RF meter
7 Modulation meter
8 Final bias (50ma)
9 driver balance
10 AM power
11 SSB power
12Modulation

This is what I found on one of those CB CD's with the tune up info

I dont know how accurate though but 10 and 11 are correct
 
i must second this mod.

i am VERY pleased with the results.
and you dont have to worry about being long winded like with hot rodded audio and a volted final.LOL
loosecannon
 
I found this somewhere so I don't know how acurate it is.

L48 Carrier frequency Maximum
L47 TX Mixer frequency Maximum
TP10
RECEIVER
L4 L5 L6 RF
L7 L8 L9 L10 1st. IF
L12 L13 L14 L15 SSB IF
L3 AM IF
L1 L2 NB/ANL IF

Internal S-Meter VR1 AM
Internal S-meter VR2 SSB
TRANSMITTER
TP8 VR9 Driver Bias 10mA
TP7 VR8 Finale Bias 100mA
L46 L45 L44 L38
VR4 Modulator Balance


VR10 AM Power 15 Watt
VR11 SSB Power 20 watt
Internal Power Meter VR6
 
MADMAXS 455 said:
I found this somewhere so I don't know how acurate it is.

L48 Carrier frequency Maximum
L47 TX Mixer frequency Maximum
TP10
RECEIVER
L4 L5 L6 RF
L7 L8 L9 L10 1st. IF
L12 L13 L14 L15 SSB IF
L3 AM IF
L1 L2 NB/ANL IF

Internal S-Meter VR1 AM
Internal S-meter VR2 SSB
TRANSMITTER
TP8 VR9 Driver Bias 10mA
TP7 VR8 Finale Bias 100mA
L46 L45 L44 L38
VR4 Modulator Balance


VR10 AM Power 15 Watt
VR11 SSB Power 20 watt
Internal Power Meter VR6

Jeesh, a 15w carrier with a single 1969 final?
That radio wont be lasting too long or sound good :)
 
hotrod said:
need some vrs for this radio
ssb power/alc
am power/dk
amc/modulation
ive found on one site modulation is vr10
but on another i dont remember which one now been a few years but said vr7 was modulation.i thought vr7 was modulation meter.like i said its been several years
i tried cbtricks.com but nothing

Remove TR24 and that opens up the SSB and AM modulation.
VR10 for AM carrier watts. Simple!!!
 
ok so what ive read is
change R131 to a 4.7K
change R114 to a 10K
680 uF at C18 can i try a 1000uF instead ??
and remove C174 and add a 1000uF cap
to the base of TR41...
Did i miss anything ??

Im thinking of upgrading most of the caps in the modulation stage as well... any thoughts on which ones ??
and for very bright meter replacement lights ??
where do i get those ?
and i have a (recieve) light out as well..what can i put in there to replace that light ??
is there any power supply mods that can be done to the radio??

AMPOWER
 
yes, you can use a 1000uF cap at C18.
i do.

when you remove C174, the negative lead of the 1000uF cap goes in the negative hole left by C174.
the positive lead of the cap goes to the base of TR41, which BTW, should be changed out to a 2N6487, or at least an NTE152.

change C172 to a 2200uF 35-50 volt cap.

i like to put R131 on a switch, but these days, i just remove TR26, and run the mic gain at 12 o'clock unless i need more for some reason. (never do)

change C46 to a .22uF monolithic cap.

replace the 2SC1419 (or 1135) in the power supply with a 2N6487, or NTE152.
replace the filter cap in the power supply with a 5600-6800uF 50volt cap.

as for the meter lights, just use white super bright LED's with a 470-680 ohm resistor.
if you buy 10-15 of the white LED's you can replace all of those lights, ON AIR, RECEIVE, etc...

i highly recommend replacing the electrolytics in the freq. counter if you have the skill (double sided, plated through PCB).

of course there are other mods, such as replacing TR14 with a 2SC2999, replacing TR19 with the 2SC1674 you just removed from TR14's spot, replacing diodes D1,2,21,22, with 1N6263's, or NTE583's. this will improve the receiver's and the noise blanker's function.

good luck with my favorite radio,
can you tell?LOL
loosecannon
 
as for the electrolytic caps in the modulation section, just replace those with 16 volt high temp. equivalent values.
really, you should just replace ALL of the electrolytic caps in the radio. solves many headaches in an old radio.

dont worry about the tantalum caps, ive been told that they hardly ever go bad.
later,
loosecannon
 

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