I know the book says 14V, but what is the REAL by-gosh MAX supply
voltage. I have a dandy supply from some sort of computer
that puts out between 15 and 16V no-load and want to know if it is
safe to use at home.
I just picked up the unit from a local who is going into a rest home
and essentially leaving the hobby.
I would suggest that you respect the manufacturer's maximum voltage
unless you want to take responsibility for you actions.
Yes, most any voltage may work, but there is a breakdown point
somewhere, and if you increase the voltage gradually, you will find that
point for your K3 - it may be an expensive experiment, but destructive
testing is like that.
On 3/6/2011 8:30 PM, Allan Taylor wrote:
> I know the book says 14V, but what is the REAL by-gosh MAX supply
> voltage. I have a dandy supply from some sort of computer
> that puts out between 15 and 16V no-load and want to know if it is
> safe to use at home.
> I just picked up the unit from a local who is going into a rest home
> and essentially leaving the hobby.
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OK, I was just reminded that the question was about the KX1 and not
the K3, but the same point applies to any piece of electronic equipment,
no matter what the model designation may be. Apply higher than the
specified voltage at your own peril.
On 3/6/2011 9:22 PM, Don Wilhelm wrote:
> I would suggest that you respect the manufacturer's maximum voltage
> unless you want to take responsibility for you actions.
> Yes, most any voltage may work, but there is a breakdown point
> somewhere, and if you increase the voltage gradually, you will find
> that point for your K3 - it may be an expensive experiment, but
> destructive testing is like that.
> Don W3FPR
> On 3/6/2011 8:30 PM, Allan Taylor wrote:
>> I know the book says 14V, but what is the REAL by-gosh MAX supply
>> voltage. I have a dandy supply from some sort of computer
>> that puts out between 15 and 16V no-load and want to know if it is
>> safe to use at home.
>> I just picked up the unit from a local who is going into a rest home
>> and essentially leaving the hobby.
There has been much discussion about kits and homebrewing in another thread,
and the question about max voltage for a KX1. The KX1 is a fairly simple
radio, so its possible to start to analyzing the factors that would
determine max supply voltage. Of course, Don's suggestion (warning) that its
best to follow the manufacturer's value is the safest.
The portions of the radio that run on internally regulated voltages will be
safe if the regulator input is not exceeded. The regulator input limit is
pretty easy to determine. But its not quite that simple, as the voltage to
the regulator is increased, so is its power dissipation.
The remaining parts of the radio that get unregulated voltages would have to
be evaluated individually. I'm too lazy to look up the schematic, but I
suspect the final audio amplifier runs off the unregulated input. Again the
specs on the device would give info on how much the input voltage to the
radio could be. Nothing much fancy about that.
My greatest concern would be the output transistor in the transmitter. Here
things get complicated. The specs for DC voltage limits give an upper limit
to supply voltage. But since we have some inductance and tuned circuits
involved an AC analysis would be required. To further complicate things, the
antenna SWR would come into play. Not simple at all!
Once past the final stage, a look at the driver would be needed too.
Well that's a beginning to the analysis. Hopefully others can add some
comments and analysis. A lot can be learned from kits when you go beyond
just assembly. Is it the same as designing a rig from scratch? No, not quite
the same thing. But being able to really analyze design gets one close to
being able to do design work.
Adhering to the instruction manual stated limits is good advice.
On the other hand, check out the schematic and see what parts the supply voltage feeds directly. Only the TX driver and PA, and voltage sense input to MCU chip. The rest is fed by 78L05 and 77L06 regulators. 77L06 data sheet says max input voltage is 16.74 volts. I would certainly not exceed that voltage.
Aside from frying that regulator, the other possibility with too high voltage may be oscillation or thermal runaway in the driver and/or PA transistors. Maybe that could happen below the max input voltage of the 77L06, but I sort of doubt it. The driver and PA transistors are not exotic parts or SMD, so it would not be real hard to replace them if you did smoke 'em.
I have been running mine on 14.9 VDC (according to the onboard "bAt" reading), not because I want to push it to the limit, but rather because the HT charger power supply I found, that conveniently plugs right into the KX1, happens to deliver that voltage. I get about 6 watts out, and haven't smoked any parts yet.