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any mods available 4 cobra 135xlr channel & power

radioreddz

W9WDX Amateur Radio Club Member
Nov 20, 2005
367
107
53
so. maryland
have a cobra 135xlr that i have had for at least over 20 years. its factory just as it was out of the box. frankly its one of the best radios that i have ever owned receive and transmit is excellent with no problems. want to know are there any channel mods and mods to increase power and maybe a swing kit to dial a watt when i want to run my base amp. :?
 

El Chop Chop

TC5080P:
Browning Baron, Cobra 132XLR/135XLR, Tram D62: <L7, L3, R134-AMC, R130-ALC>

TC5080P (Toshiba)
Substitute: ECG1207 (Sylvania)

P0 1| |16 Vdd <--(Good place to get your +5v)
P1 2| |15
P2 3| |14
P3 4| |13
P4 5| | 12
P5 6| | 11
P6 7| | 10 DO*
P7 8| | 9 Vss <--(Ground)

*Divider Output to TC5081

A simple binary Programmable Divider, used along with the TC5081 Phase Comparator and the TC5082 Reference Oscillator and Divider.

Pins P0-P7 control the frequency. Pn is binary, meaning P0 has value of 1 and P7 has value of 128. Changing the voltage (usually +5v or Ground) of the pins will change the output frequency (or "Channel") accordingly by driving the VCO up or down accordingly.


Example: You're on Channel 19 (27.185 MHz) and you read the pin outputs and notice that Pin 6 (n=32) is grounded. If you were to add +5v to that pin, the radio would be "driven up" 320 KHz to channel 27.505. Voila, extra channels!

There's more to it than this, but this should get you on your way.
 
Re: El Chop Chop

ButtFuzz said:
TC5080P:
Browning Baron, Cobra 132XLR/135XLR, Tram D62: <L7, L3, R134-AMC, R130-ALC>

TC5080P (Toshiba)
Substitute: ECG1207 (Sylvania)

P0 1| |16 Vdd <--(Good place to get your +5v)
P1 2| |15
P2 3| |14
P3 4| |13
P4 5| | 12
P5 6| | 11
P6 7| | 10 DO*
P7 8| | 9 Vss <--(Ground)

*Divider Output to TC5081

A simple binary Programmable Divider, used along with the TC5081 Phase Comparator and the TC5082 Reference Oscillator and Divider.

Pins P0-P7 control the frequency. Pn is binary, meaning P0 has value of 1 and P7 has value of 128. Changing the voltage (usually +5v or Ground) of the pins will change the output frequency (or "Channel") accordingly by driving the VCO up or down accordingly.


Example: You're on Channel 19 (27.185 MHz) and you read the pin outputs and notice that Pin 6 (n=32) is grounded. If you were to add +5v to that pin, the radio would be "driven up" 320 KHz to channel 27.505. Voila, extra channels!

There's more to it than this, but this should get you on your way.
wow you have me lost on this one
 
maybe a mosfet conversion? should be simple enough and CHEAP
I fail to see why anyone would do a Mosfet conversion to a working radio....If it is already blown up and no replacement final to be had for a decent price it is a viable option, but these radios work just fine with the finals they have....
Find a service manual and give the radio a proper tune, and leave it alone.
If you Must have more an Amp is in order.

L-3 and L-7 are inductors in the RF chain that are tuned during an service.


73
Jeff
 
I fail to see why anyone would do a Mosfet conversion to a working radio....If it is already blown up and no replacement final to be had for a decent price it is a viable option, but these radios work just fine with the finals they have....
Find a service manual and give the radio a proper tune, and leave it alone.
If you Must have more an Amp is in order.

L-3 and L-7 are inductors in the RF chain that are tuned during an service.


73
Jeff

BINGO
 
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I fail to see why anyone would do a Mosfet conversion to a working radio....

super cheap to do yourself and when done with the proper companion parts it is possible to make 35-50 pep... I just did one a few days ago that does 48 pep...

I would like to see a stock Cobra 29 final do that
 
I just did a mod on a Cobra 135xlr.
Pin 7 and 16 on a switch, (I used the "auto" switch) will give you 41-58.
The clarifier mod works but its pretty ridiculous, goes down-up 2-1/2 channels.
2015125.jpg

Clarifier:
Cut the PC board on each side of the voice lock control, Run a wire from one side to ground and the other side to the Gray wire on the PA/CB switch. Clip Diode CD304.
 
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Maybe late but thought I'd help, you could do an NPC JP36 like mod. Follow instructions for the 29 JP36 but make a cut in the foil run to C11/L11 junction, negative to the C11/L11 other end to other side of foil cut.
image.png


1) 220uf (16-25 volt) electrolytic capacitor (the 470uf version will also work and people have also used a 1000uf version)

2) 33ohm, 68ohm or 100 ohm (1/4 to 1/2 watt) resistor (ohm resistance determines deadkey, more ohms=lower deadkey)
 
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I realize this is an old post but the info above I assume he meant to say L7 junction and how about a mosfet mod did anyone ever get there and some lower channels would be nice if anyone has info on that.
 

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