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Radio Make and Model: cobra 148 gtl philly made june 1993
PCB Number:
PLL Number: mb8719
Test gear available: freq counter,bird meter,dummy load,10amp power supply,soldering iron.1000hz generator
Symptoms:not high enough dead key. vr-10 wide open

What is working: radio is working

What has been tried: change a few parts=1969final,2166driver,1973pre-driver,tr4-upgraded

Did it suddenly happen ?:no
Anything else that may be of help?: this is a 2 part question

#1=ok i have found 2 different suggestion for the 148 gtl audio mod 1 says to cut the trace of the middle leg of tr-24 and add a 1k resistor .
then another one says it is tr-26. i just want to do this one time is it tr-24?? the rite one or is it tr-26.????
thanks

#2=i have change the final 2 times the driver 2 times and the pre-driver
also upgraded tr-41=am regulator with vr-10 wide open the radio only highes dead key is 4 1/2 watts. ssb is fine 15 bird watts on average
am 2 watts dead key swing bird average to 5 1/2.
vr-9=25milli amps vr-8=50 milli amps what else can i look for or change .???
yes i know these radio are not power house but only 4 1/2 watts wide open
i've seen 3 other 148 that dead key 6 watts. thanks

hi,is this a mk1 or mk2,i had this problem before,,and got round it by spreading/opening the coils slightly,

Temporarily disconnect the base of the 2SC2166 driver. Dead key on AM (the radio will not actually transmit a signal).

Measure the voltage on the collector (metal tabs) or the driver / final. Are you getting about 6V?

I've only ever seen this on radios where noobs have fitted so called "swing kits" to them.
These work be reducing the collector voltages to the driver/finals, causing the modulation to go way above 100% and making lots of distortion in the process.

With the AM carrier level set halfway (and no RF on the finals to cause silly readings) you should have about half the supply voltage on them... in other word, 6 to 7 volts on AM TX.

If this voltage is correct, then you could have another problem, such as an incorrectly aligned RF or mixer stage.

i did as you describe but it check out ok there was never a swing kit on the radio when i got the radio only the clarifier mod and tr24 was remove.??

Someone may have changed a range limiting resistor on the carrier level adjustment circuit, or (much less likely) you have a wrong / faulty component somewhere:


The resistor circled in red limits the maximum deadkey that can be set with the trimpot, increase it (to say 10K) to get more carrier out of the adjustment.

This may be for a later Cobra version by the way - if you have a circuit for yours compare them before ripping components out.

Cheers

thanks r196 was change to a 270ohm to lower the dead key carrier. i change it to 10k but the deak stay the same.
i think the problem lies in the driver section as if you volt the final the problem is solve but i don't want to volt the final
or maybe in the am regulator section. not been the regulator at fault.???