Current drain on 6300 ...

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  • Updated 4 years ago
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I have had my Flex 6300 for a short while and run an Alinco switching power supply that is good for over 32 amps. I usually have it set to monitor volatage. So, I really did not check the current drain right away. However, I checked it yesterday and see that in receive mode it pulls about 1.7amps - which is what the documentation says it should be.

However, on keying the rig in sideband with either the MOX or the microphone it draws approx. 5.7 amps - with NO modulation or RF output indicated by my inline tuner/watt meter..

when I modulate it, it or course pulls a lot more current and shows good RF output.

I can disconnect the microphone and key it only with the MOX button and it still shows same thing - 5.7 amps and NO output is shown on MY watt meter or indicated on the SmartSDR software interface.

I tried it with the Flex mic that came with the rig, my Kenwood MC60 wired for the flex, and without a mic connected at all just using the MOX button on SSDR (ver. 1.4.3).

Always about 5.7 amp drain with NO power out showing. About 1.7 amp on receive, and when I modulate it, of course shows RF output and increased amperage drain as I would expect.

All of this was on Upper and Lower sideband and tested on several bannds.

Is this normal? The rig gets good output and works great AND gets great reports on signal level AND audio quality. I just never saw a rig pull that much current with the transmitter keyed on SSB with no modulation.

So ..... just wanted to know ... Is this mostly normal?

---Gary WB8ROL
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Gary L. Robinson

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Posted 4 years ago

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Steve - N5AC, VP Engineering / CTO

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Official Response
The power amplifier in the radio is Class AB.  In class AB the transistors are biased up when you go into transmit mode -- meaning they are running current though them even with no signal -- because it improves linearity.  The cost of the added linearity (over Class C, say) is that it consumes more power and is less efficient.  For most hams, linearity is much more important than efficiency.  If you're not familiar with amplifier classes and the trade-offs, Wikipedia has a lot of info (as does the ARRL handbook, I'm sure):

Amplifier Classes