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How Does Voltage Get to the Finals? #QMXplus

 

One thing that I haven't figured out yet is how the power gets to the finals. I don't understand how a 12 Volt supply is equivalent inside the radio to a 9 Volt supply.? Yes there is a transformer that is wound differently for either type of supply.? But is the voltage delivered to the finals the same whether the supply is 12 V or 9 V?
?
The reason I am asking this is that I choose a 9V supply.? I use a 4 cell lithium ion pack (16.8 V) and I have a voltage regulator to bring this down to 9.00 Volts.? When I go into the Putty diagnostics, the voltage at the finals is always shown as 7.5 Volts, regardless of the band.? I checked and the voltage supply stays a constant 9 Volts during key down.
?
So my questions are:?
1)? Is the voltage to the finals the same regardless of the voltage (9 oe 12) chosen for the power supply?? ?
?
2) Why are there so many warnings about not going above 12 Volts (I assume for the 12 Volt supply), but no warnings about going over 9 Volts for the 9 Volt supply?
?
3) Is everyone else getting 7.5 Volts to their finals regardless of input supply voltage, or do I have a problem?
?
Thanks for all the help.
?
Steve, W2MY
 

Steve, the power to the finals goes through Q507 to L502 and then to the center tap of the primary of T501. The two ends of the primary winding of T501 then go to the drains of the finals. Look at the schematic to follow it per the above. The schematic label is "+12v" but that implies?+9v if that's the supply you are using. There will be some voltage drop along the way, but the voltage at the finals will be a little less than whatever the input voltage is set to.? Also, the DC voltage you measure at the drains of the finals will be affected by the RF at those points. You would be better measuring that at the T501 center tap or at the drain of Q507. In the photo it appears you are getting 6.0 watts output, so I don't think you have a problem.

The warnings?about over voltage apply to both voltage levels used.?

73 .. .Ron

On Sat, Dec 7, 2024 at 11:59?AM Steven, W2MY via <stevenpituch=[email protected]> wrote:
One thing that I haven't figured out yet is how the power gets to the finals. I don't understand how a 12 Volt supply is equivalent inside the radio to a 9 Volt supply.? Yes there is a transformer that is wound differently for either type of supply.? But is the voltage delivered to the finals the same whether the supply is 12 V or 9 V?
?
The reason I am asking this is that I choose a 9V supply.? I use a 4 cell lithium ion pack (16.8 V) and I have a voltage regulator to bring this down to 9.00 Volts.? When I go into the Putty diagnostics, the voltage at the finals is always shown as 7.5 Volts, regardless of the band.? I checked and the voltage supply stays a constant 9 Volts during key down.
?
So my questions are:?
1)? Is the voltage to the finals the same regardless of the voltage (9 oe 12) chosen for the power supply?? ?
?
2) Why are there so many warnings about not going above 12 Volts (I assume for the 12 Volt supply), but no warnings about going over 9 Volts for the 9 Volt supply?
?
3) Is everyone else getting 7.5 Volts to their finals regardless of input supply voltage, or do I have a problem?
?
Thanks for all the help.
?
Steve, W2MY
 

On Sat, Dec 7, 2024 at 10:59 AM, Steven, W2MY wrote:
2) Why are there so many warnings about not going above 12 Volts (I assume for the 12 Volt supply), but no warnings about going over 9 Volts for the 9 Volt supply?
?
?
Exceed the limits of the BS170s and they expire more readily.? Higher voltage is
more power also when there is SWR issue higher current.
?
For 9 or 12V the transformer ratio is used to limit power at a given voltage.
The voltage to the final is not the same for 12 or 9V.? If that were the case
there would be no need for different transformer.

?
3) Is everyone else getting 7.5 Volts to their finals regardless of input supply voltage, or do I have a problem?
?
Nope!? But it is controlled by the MPU DAC output.
?
--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.
 

Steve,
The turns ratio of T501 from primary to secondary is higher if you build the radio for 9v instead of the more typical 12v.
That higher ratio means a 9v build running on 9v has about the same power out as a 12v build on 12v.
The turns ratio of T501 is the only difference between a 9v build and a 12v build.
The first thing to blow if you exceed the recommended power supply voltage (9v or 12v, depending on build) is the BS170 finals,
as they will be working too hard.?
Everything else in the radio should be fine at a somewhat higher power supply voltage.
?
The modulator at Q507 can be used to reduce power, such as when adjusting an antenna tuner.? Q507 is a linear voltage regulator that adjusts the voltage to the BS170's as a function of DAC signal coming from the STM32F processor.? It can only reduce the voltage to the finals, it cannot increase the voltage to the finals above that of the 9v or 12v power supply that you provide.
?
Jerry,? KE7ER

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