hi i hope you can help me i have cobra 2000 and i change all parts (justin mod). now want to know i remove TR-26 . if the the driver and final biased at 30 and 60mA is good for me or other adjustement is better.where you connect the meter for each (driver and final )thanks :?:
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loosecannon
- Thread starter harley66
- Start date
hi harley66,
the wording of your post makes it a bit hard to determine exactly what information you require, but here's what i think you want to know.
yes. remove TR26. i tried it both ways, and got better reports with it removed.
there was really no difference in TVI with the transistor in or out.
with this mod, i tend to run my mic gain at 12:00 (halfway), and i turn the gain on the mic up just until i get full swing and modulation. turning it up past that point just increases the background noise.
when i need a bit more audio to be heard in the distance, i turn the mic gain (on the radio) all the way up, and get heard!
as for the biasing of the driver and final, 30mA and 60mA is just fine.
best of luck, i hope i was of some help,
loosecannon
the wording of your post makes it a bit hard to determine exactly what information you require, but here's what i think you want to know.
yes. remove TR26. i tried it both ways, and got better reports with it removed.
there was really no difference in TVI with the transistor in or out.
with this mod, i tend to run my mic gain at 12:00 (halfway), and i turn the gain on the mic up just until i get full swing and modulation. turning it up past that point just increases the background noise.
when i need a bit more audio to be heard in the distance, i turn the mic gain (on the radio) all the way up, and get heard!
as for the biasing of the driver and final, 30mA and 60mA is just fine.
best of luck, i hope i was of some help,
loosecannon
ok, here's how you want to tune the radio after you do the mods.
set the radio on ch.19 or 20.
mic gain all the way up.
AM mode.
set VR10 for about 2 watts. (dead carrier, no modulation)
the reason for this is so that the radio does not get hot during the tuning process. we will change it later.
using only a plastic or wooden tool, tune these cans in this order, while saying "ahhh" into the mic in a normal voice level.
while doing this, watch the PEP watts on your wattmeter, and tune for maximum. (slowly!)
L47, L48, L46, L45, L38.
DO NOT TURN L36 AT ALL!!!!!!!!
even though it looks just like L38.
it is your TVI adjustment, and is already set with very expensive test equipment. heed my advice and dont touch it.
now, put the radio in LSB mode. mic gain all the way DOWN.
you will need a VOM, digital or analog, doesnt matter, and it needs to be able to read milliamps. (mA) up to about 100 or more.
set the meter to read mA in a range that will show 30-60mA.
looking inside the radio, with the component side up, and the knobs facing you, look to the rear right of the chassis.
see that small transformer?
look in front of it. you should see two wires that have connectors on them, which are plugged into the PC board.
usually these wires are purple and green, but they might not be.
looking at where the connector meets the PC board, you will notice the markings "TP8" and "TP7".
TP8 is for the driver and is adjusted first.
TP7 is for the final and is adjusted second.
using a pair of needle nose pliers, and being VERY careful and precise; pull the connector from TP8.
using an alligator clip on one of your VOM leads, connect one lead to the connector, and the other lead to the pin on the PC board.
key the mic.
if the meter reads backwards, switch the leads.
with the mic keyed, adjust VR9 for 30mA.
re-connect the driver bias wire to the pin on the PC board.
now we are going to repeat that process with TP7, and VR8, and adjust for 60mA.
re-connect the final bias wire to the pin on the PC board.
turn the mic gain all the way back up.
while saying "ahhh" into the mic; adjust VR11 for about 15-18 watts PEP. (this is where i set it. you may have different preferences, just dont overdo it)
go back to AM mode, and turn VR7 all the way up.
now turn the mic gain all the way back down and adjust VR10 for whatever you want your deadkey to be.
some words from my experience. (not preaching)
if you are running a 2 pill amp using 1446's or 2290's, set the deadkey for 2.5 to 3 watts. no more.
if the amp uses 2879's, then you can set it at 4-5 watts.
if you are running the radio barefoot, set the deadkey at 5 watts.
do not set the deadkey below 2 watts.
it really makes the radio sound bad, and will decrease your transmitting range. (these are just my opinions based on my findings)
you should be all set.
if everything went well, you should be swinging 20-25 watts PEP. (i usually see about 20-22)
oh, BTW, you really should increase C172 from a 1000uF to a 2200uF, or even a 3300uF 25 volt electrolytic capacitor.
this helps with modulation peaks.
TR24 should be intact and unmessed with.
C18 should be changed to a 1000uF 16-25 volt cap.
best of luck,
i really like this mod, as it is loud, but still maintains a great voice quality.
later,
loosecannon
set the radio on ch.19 or 20.
mic gain all the way up.
AM mode.
set VR10 for about 2 watts. (dead carrier, no modulation)
the reason for this is so that the radio does not get hot during the tuning process. we will change it later.
using only a plastic or wooden tool, tune these cans in this order, while saying "ahhh" into the mic in a normal voice level.
while doing this, watch the PEP watts on your wattmeter, and tune for maximum. (slowly!)
L47, L48, L46, L45, L38.
DO NOT TURN L36 AT ALL!!!!!!!!
even though it looks just like L38.
it is your TVI adjustment, and is already set with very expensive test equipment. heed my advice and dont touch it.
now, put the radio in LSB mode. mic gain all the way DOWN.
you will need a VOM, digital or analog, doesnt matter, and it needs to be able to read milliamps. (mA) up to about 100 or more.
set the meter to read mA in a range that will show 30-60mA.
looking inside the radio, with the component side up, and the knobs facing you, look to the rear right of the chassis.
see that small transformer?
look in front of it. you should see two wires that have connectors on them, which are plugged into the PC board.
usually these wires are purple and green, but they might not be.
looking at where the connector meets the PC board, you will notice the markings "TP8" and "TP7".
TP8 is for the driver and is adjusted first.
TP7 is for the final and is adjusted second.
using a pair of needle nose pliers, and being VERY careful and precise; pull the connector from TP8.
using an alligator clip on one of your VOM leads, connect one lead to the connector, and the other lead to the pin on the PC board.
key the mic.
if the meter reads backwards, switch the leads.
with the mic keyed, adjust VR9 for 30mA.
re-connect the driver bias wire to the pin on the PC board.
now we are going to repeat that process with TP7, and VR8, and adjust for 60mA.
re-connect the final bias wire to the pin on the PC board.
turn the mic gain all the way back up.
while saying "ahhh" into the mic; adjust VR11 for about 15-18 watts PEP. (this is where i set it. you may have different preferences, just dont overdo it)
go back to AM mode, and turn VR7 all the way up.
now turn the mic gain all the way back down and adjust VR10 for whatever you want your deadkey to be.
some words from my experience. (not preaching)
if you are running a 2 pill amp using 1446's or 2290's, set the deadkey for 2.5 to 3 watts. no more.
if the amp uses 2879's, then you can set it at 4-5 watts.
if you are running the radio barefoot, set the deadkey at 5 watts.
do not set the deadkey below 2 watts.
it really makes the radio sound bad, and will decrease your transmitting range. (these are just my opinions based on my findings)
you should be all set.
if everything went well, you should be swinging 20-25 watts PEP. (i usually see about 20-22)
oh, BTW, you really should increase C172 from a 1000uF to a 2200uF, or even a 3300uF 25 volt electrolytic capacitor.
this helps with modulation peaks.
TR24 should be intact and unmessed with.
C18 should be changed to a 1000uF 16-25 volt cap.
best of luck,
i really like this mod, as it is loud, but still maintains a great voice quality.
later,
loosecannon
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