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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George Molnar, KF2T, Elmer

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Sounds reasonable.
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Steve N4LQ

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That's about what my 6500 does. 
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Jim K4JAF

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I cant read as fine on my meter (analog), but 5.7 looks correct, mine is between 5 and 6.

Not sure what class they run the finals in either.  If your getting good reports, just enjoy.

73s Jim K4JAF


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Steve N4LQ

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Not exactly an efficient QRP rig.

84 watts consumed with zero output!!
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Gary L. Robinson

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Thanks guys! That's what I wanted to hear! I have had no problems with the rig, I just wanted to make sure that was normal behavior. Other than the first QSO I had, I have had fantastic reports with this 6300. And the first QSO was with the hand mic that came with it -- and I had the switch on the back of the mic in the wrong position. Operator error hihi!
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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
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Steve N4LQ

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You are quiet correct Steve. It's just ironic when operating QRP CW that when running 5 watts output you are consuming 50 watts not to mention whatever the computer is using. But then this wasn't meant to be a portable QRP rig either. 
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k3Tim

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Yes, got it....  
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Steve N4LQ

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Yes...It's comforting to know that we have a rig slightly more efficient than a 160 meter hamstick mounted on a ground rod.
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k3Tim

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If you read Steve's post and study over class AB, you will see the reasoning and the trade off.  Be thankful the PA isn't pure class A or you'd be burning 100+ watts at idle.  Compared to my Novice days (Drake-1A / Knight T60), just lighting the filaments took more than 50 watts.

Using QSK CW there'is no bias draw during key up.
 
On SSB, VoX similarly has no bias except when xmit.

The VoX  is the  best I've ever used as it doesn't clip the first syllable and super smooth.

All good!

_..--
 k3ITiM
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Steve N4LQ

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Indeed. I agree with that Tim. QSK is the best!
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Gary L. Robinson

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And, of course, there is no trade off 'penalty' on my favorite sound card digital modes since they are modulating the DIGU signal constantly while keyed. And Steve's post made it real clear by pointing out that the amplifier is a class AB. It's just been a long time since I used a rig like that had a class SB amp section :-)