Ok I know that some will say its not worth it before I begin! I was wondering when adding the 2nd mosfet to a 949/959.... On cbtricks its going off of the 1969 version it really doesn't show biasing the 2nd mosfet with a companion part. Wouldn't it need the same biasing. Just curios!!! Now I am working with the mosfet edition already, so I'm assuming I could shadow the parts as in the single final stage.. Thank you for all help. I am trying to understand more about how these things work..
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galaxy dx 949 dual final mod biasing ?????
- Thread starter doc919
- Start date
Don't know the precise gate voltages for MOSFET's, but with a Beta Matched Pair of 2SC1969 finals in a DX-949 or DX-959, a good starting point for bias adjustments would be:
25 mA for the driver transistor
and 50 mA for the Finals.
25 mA for the driver transistor
and 50 mA for the Finals.
3.5-4v on the 'gate' pin is the typical bias voltage for MOSFETs final & driver . . . Any more than that, they'll get too hot and may fail . . .
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after reading his question he is saying what do you need for biasing, I think he is not asking the proper quesrion. seems he is asking what parts are needed to complete the circuit. at least that is what I am thinking since he mentioned a companion part. you guys gave him the answer to what he is asking.
yes I have my gate voltage set & 3.45+-. Just wondering if I set up the second irf520 in the second stage then wouldn't I need a companion part for that transistor( doesn't show one one on the CB tricks site. I know I could shadow the parts as in the first final. Guess what I am curious about is would it show/have more output by adding the companion part to the second final. With it set as in the way it is on"cbtricks" I am showing 20watts on low power40 watts pep on high. Would there be an advantage of having it biased properly in both stages???? Thank you all again!!
Just got a 959 that has a single MOSFET final; and the driver is also a MOSFET.
I set both gates @ 4v each, works well there.
Sounds like yours is working fine.
Did you add a heat sink?
It will need one now. . .
I set both gates @ 4v each, works well there.
Sounds like yours is working fine.
Did you add a heat sink?
It will need one now. . .
Yes ,I do have a heat sink for it, but was wondering more along the lines of where is the 2nd mosfet final getting its biasing from on the "cbtricks" site. Thank you again
I think he is talking about this.
http://www.cbtricks.com/miscellaneo.../galaxy_dx949_959_2547_erf2030_mod_rev1-2.pdf
http://www.cbtricks.com/miscellaneo.../galaxy_dx949_959_2547_erf2030_mod_rev1-2.pdf
Well, if he is going by that page, then it shows two MOSFETs in parallel using the same biasing device.
That doesn't make much sense. That is, to put another MOSFET in parallel with the other. There is no means with that method to adjust the bias voltage either. Guessing that the 33K resistor could be replaced with a 100K pot. The radios that have the factory MOSFETs use a zener diode as bias regulation. Perhaps some of the gurus can shine some light on this. That is, the difference between the CB Tricks page and the Galaxy circuit.
http://www.cbtricks.com/radios/galaxy/dx959_mosfet/graphics/dx959_mosfet_sch.pdf
That doesn't make much sense. That is, to put another MOSFET in parallel with the other. There is no means with that method to adjust the bias voltage either. Guessing that the 33K resistor could be replaced with a 100K pot. The radios that have the factory MOSFETs use a zener diode as bias regulation. Perhaps some of the gurus can shine some light on this. That is, the difference between the CB Tricks page and the Galaxy circuit.
http://www.cbtricks.com/radios/galaxy/dx959_mosfet/graphics/dx959_mosfet_sch.pdf
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looks as if jumping C209 and C210 together you are using the one companion part for both to set the bias. have never tried this mod before. I would just set them up as a 2517 radio to get them all the same. seems as if that would be the easiest way to do it.
Ok thank you all again. I will look up the parts list for the 2517 or like board to compare. I was kinda thinking that the biasing wouldn't be set properly by that method, bit hey I'm a newbie/beginner/rookie to all this.
Right.
The 2517 schematic of dual final MOSFETs makes real sense.
http://www.cbtricks.com/radios/galaxy/dx2517_mosfet/graphics/galaxy_dx_2517_mosfet_sch.pdf
The 2517 schematic of dual final MOSFETs makes real sense.
http://www.cbtricks.com/radios/galaxy/dx2517_mosfet/graphics/galaxy_dx_2517_mosfet_sch.pdf
Attachments
if you set it up like the 2517 it will have all the parts as a single circuit for each final. it will have the bias pot adjustments etc for each final. the one on cbtricks just has you jumping C210 and C209 to eliminate the other parts in the circuit. may work just fine but like I said earlier I never tried it that way myself.
one thing on the 959 radio I found that you have to change parts in the audio chain also to make a 959 or 949 put out like the factory duel final radios. the 1st one I did would not swing until the audio circuit was set up like the duel final radios.
one thing on the 959 radio I found that you have to change parts in the audio chain also to make a 959 or 949 put out like the factory duel final radios. the 1st one I did would not swing until the audio circuit was set up like the duel final radios.
here is a link to the mod Bennie and Rick from euro radio drew up for the gual final mod. this is the one I have done before. had to look it up and Rick found it.
http://www.cbtricks.com/miscellaneous/fet_papers/mosfet_conv/graphics/6900xxx_ssb_mosfet.pdf
http://www.cbtricks.com/miscellaneous/fet_papers/mosfet_conv/graphics/6900xxx_ssb_mosfet.pdf
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