Magmun S9 late version bias setting

[357]

I cant find the bias setting for the late version? S9.

It has 2 jumpers, TP8 and TP9

The board looks like this:

 

[357]

Looks like I need to find the carrier offset test point too.
R151 is not as shown and no IC3 there either.

 

[357]

should I just set them to 3.65v?
does the dots mean anything?

 

[Handy Andy]

Well, if you set for 3.65 volts you may miss the proper trigger points - the Jumpers need to be removes and you set up your DVM onto the posts for reading Ammeter - you set Driver no more than 50mA in TX mode into a Dummy Load and the Finals since there are tow - you should do about 60mA no more for safety margins...

Why Ammeter versus voltage?

You can't see the "Trigger" unless you look for the RAPID and I Do Mean RAPID rise in current as they begin to switch on, that may be at a different voltage than you would think...

Heres where they are in your pics - thanks BTW - this helped...


Hope this helps!
​

 

[357]

Thank you Andy. I posted on copper but the thread never got approved.
I set them to 100ma as the service manual says but it got hot pretty fast for my liking.
I then set them to 50ma and the voltage was almost 3.8v. I'll try to verify that.
Too low and it sounded crunchy, too high and she gets hot.

Should I set the current at 14.4v or 13.8?


Any chance you know what frequency to peak the rf chain?
The instructions are lacking

 

[Handy Andy]

You set "current" by what you want to run it as Standard...

You can ALWAYS RUN LESS VOLTAGE and She will do fine...

So again, because of the variance of voltage, the "mA settings" are more of a best guess - you still have to run a SEPARATE audio check while adjusting...

Re-read that upper HTML style Bias Adjust - they suggest CENTER Band USB mode...

• Run your Mic Gain at Minimum to initial "settings" then "slowly" bring back Mic Gain up in voice drive
• - note the low-levels of audio try to get lowest levels of distortion and pinching
• - you want the best passage of audio whisper to start with
• - adjust Bias for that portion (Driver or Final) for best audio
• - then adjust Mic Gain up
• - then check for heating
• - you will always have these dynamics
• - so run ALC on (VR12 5K) and watch peaks as you bring up Mic gain,
• - watch the wattage levels too <45 Watts Max!
• - do a "best trade-off" of heat to whisper drive levels for our own operation.
• - Once Driver levels are set - do the same for your Finals...
• - don't use tone - use your voice - rest both you and radio as necessary, don't over do this
• - VR12 (5K) or 502) is ALC for SSB adjust - look for and adjust RF Peak to keep BELOW 45 watts - else you will be regretting skipping this step...

Use tones for Tuning - no...

Audio "ahh" sound works best - for the pass filtering is more for the audio passband and it's tones - don't try to use a single 1kHz or dual tone - just your voice - using the microphone you will be using the most - for best results.

 

[357]

thank you Andy.
I set the driver to 60ma and final to 80ma and volts are 4.020 and 4.060.
I hear a audible white noise as I increase the bias current.
I tested it like this and it sounds clear, not too hot.

I guess its as good as its gonna get

 

[Handy Andy]

Thanks for the feedback...

And I guess setting the voltages to the levels posted earlier would have been too low. So thank you for using the mA approach versus the "set the volts" (V).

(If that is all you wanted to know from me - ... you can stop here - but for those still satiating for more...)

Because of an article I wrote (vented on) earlier - that was more for the describing of why older boards that used Bipolar and then you converted over to MOSFET - you had several limitations - including the god-forsaken values the potentiometers; had to be increased to, in order to even provide a "Window" for the Gate to work in and operate.

Back then Bi-Polars had a "Knee" you simply tweaked the Bias CURRENT to best provide the slope of power to keep the Transistor Biased into Class AB (If SSB) and Class C (Class D at Collector).

In MOSFET you have a Knee - but it's in voltage "Range" the RF wave will conduct in...

So your Datasheet looks different...you have to find that voltage...but when they throw you a bias circuit set up for Current and expect you to make it (Your MOSFET) Fit and work - they changed the rules...

Typical Galaxy EPT3600-series board...Bipolar days...

​

Don't worry, I saved the MOSFET version too...

If you notice anything...no it's not a test...​

It's what you don't see - is the problem...

Both schematics are from the Galaxy line but the top one is Bipolar, the bottom lower one is their MOSFET equivalent...

Note those traces and board - THEY ARE BOTH THE SAME!

No provision for Gate voltages except for the SWAMPING of a Resistor and the Variable are 1000X higher than your initial Bipolar design...everything in there for the RESISTIVE element is 1,000X higher in values...

That's not an advancement - it's a simple adaptation approach...

So when you go back to this thread,...
MOSFET conversions for upD858 and MB8719 boards - threads About the MB8719 Bi-Polar to MOSFET approach The page in which this series of questions got raised is what made me go down a rabbit hole to try and come back with better answers as to what we should do...

One main culprit is the Parallel of the Bipolar needed a Parallel resistive approach to reduce the current load across the most vulnerable parts - mostly those being the Variable pots and the Diodes themselves. So they used resistors to share that current load to drop the voltage and just leave a good strong bias current to keep the Bipolar steady in the Class AB region...

• If you're with me so far, good - the problems that now exist with MOSFET designs is the level of voltage, with the right amount of current - flowing across the Gate - not INTO it but available when and if you want to amplify - FLOWING ACROSS THE GATE.
• If MOSFET is a Voltage-Dependent Device, why is Current even needed? To REPLENISH that which Voltage cannot replace, you are dealing with Static moments of Kinetic energy capacity - Voltage can appear, but requires a capacity - A Current - in which to flow into and out of a circuit.
• MOSFET Gates use high intrinsic insulation to keep the power at the Gate from flowing into the Substrate - else you wind up having a Transistor. But the Voltage needed to toggle the Gate on requires enough power in current - to keep the Gate working - for even the Voltage at the Gate, the power flowing underneath beyond the Insulator INTERACTS with the Gate Field - a counter EMF force - the Voltage is altered by this effect, so Current can be pushed into this Gate region to fill the voids with voltage again as a means to "wash" the Gate and keep the field stable for the length or duration of time you want the device switched on.
• Think of this BIAS - as a pressure from a pipe into the faucet and your thumb is holding back that pressure as a Static event - the pressure of your thumb can be considered the voltage - the pressure of the water is the current - if you are tying to keep a sink filled with water - but it sloshes off and drains away water a any given point in time - the level of the Sink can be considered the effort of the field, and it's interaction with "Gravity" as the work of weight the losses are, and the change in level or displacement is the effect the Sink has in drawing energy from the field as in, away from the field.
• The Bias is your job...making the flow of water into the system, strong enough to keep the sink filled, yet not overflowing - Water being drained out has weight to it, as we measure by Gravity on the water volume. When you remove a lot of water quickly - the volume of water needed to arrive thru the faucet is higher, a greater demand is produced by the loss of volume and the water weight in the sink is less - affecting the volume of water required as a force to replenish this loss of volume as a larger weigh (effort)t to restore balance.
• When the Sink is more empty, the volume of Water needed to recover the initial static level is greater. But the effort to keep the water at the Faucet is gone ,your thumb is no longer needed the Voltage you once had, is now gone, the Gate fills in the sink with water (as a process of flowing current thru that pipe) and as you approach the equilibrium of Capacity to shut off the Gate - your water in the Sink and its' weight has returned requiring more effort to maintain stability and checks and balances to maintain the level in that sink.
• So the change of the voltage the effort to fill inside at the Gate from the power flowing in as current flowing across the junction past the insulation - induces this effect of reverse EMF and the Bias needs to have enough power in both voltage level and current capacity to overcome this loss effect.
• So in shorter terms, you want to overcome the effects the Gate with exhibit when it turns on and then right off because the voltage arriving to does not have enough capacity to replenish that which the counter emf field takes away, fast in recovery or in strength powerful enough to maintain the stiffness of this threshold level..

One drawback is the SENSITIVITY the Gate has in changes to the voltages - your Tolerance issue...

You have tolerance issues in the voltage divider that is used. In the effort of millivolts and hundredths of a volt - realm small changes in divider voltage response to tolerance gives you results that are far greater in impact from temperature variances across large value substrates like those 100K pots, you lose nearly 20% of your intended value STARTING at one temperature and finding it somewhere totally different elsewhere when the thermals kick in...That's a TOLERANCE factor folks...Try keeping your Gates running right using that - you'll be in the same boat crying for the days of the 1969 and 2312 all over again...



I just wanted to point out - we don't need to Parallel resistance - we need to stack it, in series - to provide a working value for variable to handle the variances of the parts we Bias.

Then use a Fixed range of resistance (impedance if you wish to look at it this way) that can provide a better in-between tolerance drift than to attempt to use a variable with an adjustment range throughout the range of scale and it's INABILITY to stay within a TOLERABLE range of Impedance/ or Resistance (you Pick) to keep and maintain GATE bias voltages correctly.

In stacking or in-series approach - we are making a multiplier out of it (a fixed value) and we can then use a lesser values' adjustable-range pot variable to offset these trimming needs for those MOSFET Gates. Following this approach we are Lessening the tolerance range of drift compared to it's range of change to a more workable le and tolerable range and level of values for the MOSFET to work from and use for it's Gate threshold and operational parameters. The variable pot having a smaller range lessens the change of a latching event or an out of tolerance problem because we can then use FIXED values of resistors to offset the range we do not need the pot to adjust - so we can narrow down just the window and make it more efficient in dropping and changeover of other MOSFET types as either and upgrade of crossover to.

There I said it...

Have fun guys!