On a newer Galaxy radio 360014B bord what does TR 49, 50 and 51 modulation amplifiers do besides amplify AM modulation?
Thanks.
Thanks.
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360014B Board question Galaxy
- Thread starter Low_Boy
- Start date
Q49 is the Driver, Q51 is the Pre-driver, and I'm guessing that Q50 is part of some switching circuit.
According to a 3600-14b schemo.
http://www.cbtricks.com/radios/galaxy/dx2517/graphics/Dx2517sch.pdf
According to a 3600-14b schemo.
http://www.cbtricks.com/radios/galaxy/dx2517/graphics/Dx2517sch.pdf
Something is not right. That is the power section. Looking at the schematic and parts placement for the Galaxy 33HP same board number those are modulation amps. Possibly the board number for the 33 HP is wrong on cb tricks? But what else do they control?
You are right. Since the 3600-14b board is also a AM/SSB chassis, I see what you are talking about.
AM modulation/regulation.
AM modulation/regulation.
It's an AM only radio (you can have FM in it) but that doesn't mean AM Regulation is just for SSB - this is the same thing that happens in an AM/SSB radio - only there's no SSB...
TR49 takes in 8V constant as variable Carrier Power VR13 - so you set it to mix Audio from C191 from the Mic amp of the 4558 chip and uses the output of TR51 as SOURCE to combine all ingredients and mix well - and shoot it off to a pre-amp TR50 - which then goes into the big Mixing bowl TR51...and shoot that's off to the Final and Driver with a small sampling used for TR49 to recombine with newer fresh ingredients..and the cycle starts all over.
TR49 takes in 8V constant as variable Carrier Power VR13 - so you set it to mix Audio from C191 from the Mic amp of the 4558 chip and uses the output of TR51 as SOURCE to combine all ingredients and mix well - and shoot it off to a pre-amp TR50 - which then goes into the big Mixing bowl TR51...and shoot that's off to the Final and Driver with a small sampling used for TR49 to recombine with newer fresh ingredients..and the cycle starts all over.
I've seen some change out TR49 for a beefier transistor, since the original 2sc945 really gets too hot.
I can understand that.
HA what would you replace it with?
I can understand that.
HA what would you replace it with?
Wow those three components do a lot in a radio. I have seen tr51 go and the radio would shoot a 25 watt carrier and no modulation but never saw one go and not let the radio key up. The finals were switching. I had bias current. And a correct freqency. But no output. And it figures after checking voltages it was the last thing I suspected.
Thank you Andy for explaining.
Thank you Andy for explaining.
This radio from factory had a different transistor something with a 17 or 70 in the number. I am not home so i can not look it up.
If people were having "overheating" issues and or wanted more gain I'd work over on the 10K resistor between TR50 and TR51...Use a higher value to obtain more envelope attack (sharper rise)
Why would someone want to try and fix something you don't need to fix?
The current draw thru the TR49 945 is not even 1/3 an amp 200mW maybe (less than 1/4 amp) but if you've got heating issues - there's more going on - you can try a 2SC1815 version
Or aka C1815 - NPN version has a slightly higher breakdown voltage and more current capability. 250mW constant
Or you can try a Giant TO-92 like the 2SD2213 NPN Darlington - that would be fun...
Why would someone want to try and fix something you don't need to fix?
The current draw thru the TR49 945 is not even 1/3 an amp 200mW maybe (less than 1/4 amp) but if you've got heating issues - there's more going on - you can try a 2SC1815 version
Or aka C1815 - NPN version has a slightly higher breakdown voltage and more current capability. 250mW constant
Or you can try a Giant TO-92 like the 2SD2213 NPN Darlington - that would be fun...
I understand that some have changed out the 100 ohm(/) resistor feeding TR49 to a 1000 ohm to cool it off.
I've also seen that some have replaced TR49 with a NPN that had a TO-220 case (don't recall which one).
Thoughts?
I've also seen that some have replaced TR49 with a NPN that had a TO-220 case (don't recall which one).
Thoughts?
Well ,it may look "kewl" to have that done, but you need to research the reason why they chose the parts in there in the first place.
The 2SC945 was chosen for audio characteristics - it is used as a Switch, Pass Regulator and Linear Amplifier.
TR49 - if you are referring to the Base region - that may be more due to the nature of what others want to do with a 100 ohm resistor and diode - NPC Negative Peak Compression mod .
The reserves left behind in that mod is very low and a lot of base voltage is still present - forcing the transistor more on than off . That is what makes the Base heat up and get close to a Collector to Base and Base to Emitter threshold that can make (read hurt) the transistor fail.
The 2SC945 was chosen for audio characteristics - it is used as a Switch, Pass Regulator and Linear Amplifier.
TR49 - if you are referring to the Base region - that may be more due to the nature of what others want to do with a 100 ohm resistor and diode - NPC Negative Peak Compression mod .
The reserves left behind in that mod is very low and a lot of base voltage is still present - forcing the transistor more on than off . That is what makes the Base heat up and get close to a Collector to Base and Base to Emitter threshold that can make (read hurt) the transistor fail.
Here's why I feel they used that part...
And if you look at the 2SC945 - you'll see similar characteristics.
It has a Knee
It deals with Linear Operation versus ON/OFF like a switch.
If you use a switching transistor - you'll have a hard time trying to make it linear - at least not without some type of feedback...Note the 10 K used on the 2SA1869 the part of power amplifier - which if you use a feedback resistor you limit gain of the part used in the circuit.
The 2SA1869
ok had to leave keyboard to handle a family matter...
The reason for the use of the 10K is not just to limit current but also to provide a linear function - analog. The things amplifying Audio too. So you don't want the transistors to act like switches - just very good linear amplifiers over a limited range of power and current.
And if you look at the 2SC945 - you'll see similar characteristics.
It has a Knee
It deals with Linear Operation versus ON/OFF like a switch.
If you use a switching transistor - you'll have a hard time trying to make it linear - at least not without some type of feedback...Note the 10 K used on the 2SA1869 the part of power amplifier - which if you use a feedback resistor you limit gain of the part used in the circuit.
The 2SA1869
ok had to leave keyboard to handle a family matter...
The reason for the use of the 10K is not just to limit current but also to provide a linear function - analog. The things amplifying Audio too. So you don't want the transistors to act like switches - just very good linear amplifiers over a limited range of power and current.
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