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Galaxy dx959 mosfet final and driver bias voltage?

mclamb97

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Feb 6, 2010
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Could some tell me what the properdriver and final bias voltages are for a galaxy 959? cant find a service mabual for the new mosfet version online. Thanks for anyones help
 

Could some tell me what the properdriver and final bias voltages are for a galaxy 959? cant find a service mabual for the new mosfet version online. Thanks for anyones help

Sure.

1) Keep that mirrored bias board in place; do not remove it. AM or SSB mode can be used.

2) Place the "+" lead of the voltmeter on the top lead of L37* and the "-" voltmeter lead on the solid ground wire between the large metal xtal filter can and the 10.240mhz xtal. The driver voltage can be set to 3.6v using vr-12.

3) Next, place the "+" lead of the voltmeter on the top lead of L33* keeping the "-" lead of the voltmeter on the solid ground wire between the large metal xtal filter can and the 10.240mhz xtal as you did for the driver. Adjust the final transistor vr-10 for 3.5v.

4) Done.

NOT RESPONSIBLE FOR WORK DONE INCORRECTLY.

NOTE:
* = the board is marked at these locations for a choke; but they are actually resistors in the MOSFET radios at these locations. Don't let that throw you off - Robb
 
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looks as if Robb hit it right on the head for you.good job Robb, not much out there so far for the mosfet's adjust.
 
Some additional thoughts/info:

You should also turn off any/all modulation/mic gain when keying the mic when setting up the MOSFET driver/final voltages.

MOSFET transistors have a threshold or a 'turn on' voltage point. Unless there is a certain minimum voltage present at the 'gate' pin of the MOSFET, it will not pass voltage. IIRC this number varies from different mfrs; usually somewhere around ~2.8v. You can start with a smaller feed voltage ('bias') and find no output from the device. Turning it up the voltage gradually with the vr, the device will then become active/have output.

These devices will require no more than 5v; that is the other end of the voltage spectrum and not to be exceeded. But anywhere between its threshold and the upper voltage limit is usable. It is preferable to find the voltage threshold and then just increase that number by .1v. In this way, you can be sure that you will not allow the device to get overheated when operating.

If anyone else can contribute or wishes to add info for MOSFET use or any other info for the DX-959 alignment, I would be interested and appreciative. The info I already put up in the previous post was gathered from a conversation with a Galaxy tech - BTW.
 
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What's the voltage supposed to be on the irf520N mosfet , I have a 2547 Galaxy that I put those mostfets in it receive but transmits off frequently when I key the 2547 is a 959 in a base unit . I wish there was a YouTube video show how to do this since I hand on and learn better from a video thank you have a nice day
 
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Finals should not effect this, sounds like your radio is off frequency and needs aligned. Did your radio have mosfets to begin with? If not it's not a direct swap to change to a mosfet final, other things will need reworked. Last, its a galaxy, they drift.
 
The 2547 has a frequency display. If it is off frequency while transmitting, the counter should give this away.

And if the counter shows the correct channel frequency, your "sounds off frequency" symptom has a different cause.

Was this 2547 built with MOSFET finals, or is it a older version that someone modified to use them?

73
 
The 2547 has a frequency display. If it is off frequency while transmitting, the counter should give this away.

And if the counter shows the correct channel frequency, your "sounds off frequency" symptom has a different cause.

Was this 2547 built with MOSFET finals, or is it a older version that someone modified to use them?

73
It's was built with mossfets from facktory , it had irf520 as final and driver and I replace the irf520 with irf 520 Ns ,it now trans mits off freq and the radio dims when I key it up ,could the mosfet irf520N not get enough power ,I left the bias and final power alone that's all stock to the irf520
 
I’m not an authority here but I think you’d see better results if you got away from the N’s and used a regular 520.

But I have some N’s myself, never used them, so I’m curious to see the outcome of this as well.
 
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Go to Mouser.com and get the IRF520PBF. That’s what I use without issue. Others may agree or disagree.

And I will say that your use of the N possibly has absolutely nothing to do with your issue but if that’s all that was changed, I’d raise my eyebrow to it.
 
No N mosfet so for this guy either. I use the vishay 520's and they've always served me well plus they're really low cost. Any reputable shop local or online should readily have them too. Man, be careful for counterfeits because they are out there! Is it a possibility that it's a warble like ssb warble? Ssb warble can sound like off frequency. Could use a full TX alignment after a final swap like that.
 
I might be high on crack again but doesn’t the N version have a different gain or something? The bias needs to be different or something, the voltage requirement? I can’t remember, it’s been a long day.

But agreed. Get the plain 520’s and be done with it.
 

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