New Galaxy DX-959B Alignment Question

[KD8HMO]

Im playing around going through the alignment on my DX-959B. It is stock out of box new. I have not done any mods to it. Limiters are still stock. Driver and final bias are both set to 4.20v from the factory. I have peaked the amp section to get about 22w on my PEP meter with 1000hz tone. Dead key at 4 watts. Modulation set to 100% with 1000hz tone, flat topping on scope then turned back to perfect sine wave. I have a few questions now..

1. If best PEP is 22-23 watts, should dead key be set for 4 watts or higher?

2. Both bias voltages were 4.20v from factory. If i drop those to 3.5, I cant even get 4 watts dead key even turning the pot all the way up. 4.20v settings will allow up to about 9 to 10 watts. So im assuming the factory voltage settings would be correct?

3. Twice now, I have set the dead key wattage, to 4 watts, then the next day I fire up the radio, and right off the bat, dead key is only 3 watts. Anyone have an idea why that would change? Would that wattage increase after being turned on for a bit?

Thanks

 

[KD8HMO]

Also, SSB APC is set to 12.5v.

 

[sonoma]

I normally do not set a radio until it has warmed up for about 20 min to stabilize. never have checked one as soon as I turn it on. I have always done it after warm up for the system to be where it would be on freq after warm up. works best for SSB since it wants to change just a little after warm.

 

[Robb]

Never worked on a 'B' model; is it using surface mount parts?

I would never turn up the IRF50N MOSFET final/driver past 3.9v. Not unless I had a supply of extra parts around and wanted to keep changing them out. Even with a heat sink added.

2. Both bias voltages were 4.20v from factory. If i drop those to 3.5, I cant even get 4 watts dead key even turning the pot all the way up. 4.20v settings will allow up to about 9 to 10 watts. So im assuming the factory voltage settings would be correct?
Might be that the power supply/regulator is falling off in the preamping circuit before the finals under load.

Did you adjust the ALC pot yet.
Didn't say.

Feeding radio 13.8v?

 

[nomadradio]

Set the driver and final bias for no more than 40 mA.

NEVER just measure the gate voltage and call it good enough. You need to know that the current draw with no drive is below the danger point.

Can't tell that without breaking the test-point circuit and using your current meter in line with first the driver, then the final.

The driver's bias-test jumper should always be unhooked when setting the final bias. The tiny bit of carrier that leaks out on SSB transmit can introduce an error into the final's current reading with the mike gain at zero.

73

 

[KD8HMO]

I am feeding 13.8v from a 40a power supply. SSB alc is set for 12w PEP. I really wish these companies would update their manuals when they make changes or make new models. There seems to be a lot of confusion out here about final bias settings, depending on if you have the old finals or new mosfets. This radio was set to 4.20v on both driver and final out of the box, with 2w dead key. Everyone that I ask has a different idea, and i cant get a straight answer from Galaxy. The service manual for the radios with the older transistor finals says, 50ma on vr12, and 100ma on vr10. Then I am told that mine should be set to 3.80v for driver, and 3.50v for the final since it has mosfets. Set that way, i cant even get 4w dead key. It sure would be nice if Galaxy and Ranger would update their manuals...

 

[KD8HMO]

I will take a pic of the board so you guys can see it.

 

[Robb]

Never had a radio not do 4w dead key - even when cold. Never. There must be something phony going on somewhere. Not that I know what it is; I do not.

I think nomad is probably right about how to set up MOSFET biasing; as he most definitely knows his way around a radio. I never snapped a MOSFET by keeping it at/under 4v and always got everything out of it to be functional doing it that way.

Holding SSB to 12w may well be the part of the issue here, especially if you peaked the TX coils in AM mode. Once I set the final/driver biasing settings I then peak the TX coils in USB or LSB. NEVER in AM mode!

You might try to turn up the ALC; but take this route with care and check the waveform to be sure that you aren't creating any distortion in either AM or SSB mode. 18-20w is typical; but like I said - never worked on the 'B' model - either.

 

[KD8HMO]

 

[KD8HMO]

 

[Robb]

Looks pretty much the same as a non-B model; except that it is using a different audio IC. That is all the difference I've noticed. May be tons I've missed - too.

 

[KD8HMO]

It has blue LED displays and blue back lighting too

 

[Robb]

I see; the 'B' is designated for blue readout/LED display.
OK

 

[KD8HMO]

Well i set the bias down to 3.9v on both. Then I reset the dead key to 4w (it dropped down a bit). Then I peaked the amp stages again in order, on USB with ALC turned all the way up. That brought sideband PEP up to about 18w and am PEP to about 23w again. Then I reset the AMC pot and now it sounds great.

 

[Robb]

How many watts in SSB mode?

I wouldn't turn the ALC all of the way open. Put 1khz signal into the mic in SSB mode and turn it up until you see no more power output; then turn it down a little bit. Check it on the scope to make SURE no distortion is present. Adjust from there if necessary.

I also peak TX coils on ch 20 for better consistency and makes less work - rather than trying to balance power between ch 1 and ch 40. That latter is just a PITA - IMO.

Radio should be capable of putting out more watts in SSB mode that AM. Don't think that AM is suffering, I can assure you it will be at its best when tuned in SSB mode.