Ticking an old box (Commtron box~)

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Otter
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Re: Ticking an old box (Commtron box~)

Post by Otter »

un-realistic wrote: 13 Feb 2022, 00:08 is midland 100AM the same as my Commtron VIII?
Have a look at the circuit board in your radio. You should see the number 481902C. Lots of these Maxon built AM radios were based around just a couple of PCBs.
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Re: Ticking an old box (Commtron box~)

Post by un-realistic »

Fantastic Claude
thanks

Exactly the same and resistor present too - so I am right mine has broken off the signal meter black cable terminal
Great info there Cheers :D
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Re: Ticking an old box (Commtron box~)

Post by un-realistic »

See attached photo

with CB turned on I get 13,8v on the the middle leg of this transistor - nothing on the outer legs
is this normal?
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Mitch
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Re: Ticking an old box (Commtron box~)

Post by Mitch »

un-realistic wrote: 14 Feb 2022, 10:36 See attached photo

with CB turned on I get 13,8v on the the middle leg of this transistor - nothing on the outer legs
is this normal?
Yes, perfectly normal, one side is earth, middle is power and output, other is signal in.
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Re: Ticking an old box (Commtron box~)

Post by un-realistic »

Great thanks

Just looking at trying to solve the low TX power - well I should say low TX power according to the units signal meter just over 1W

Hoping with the use of a SWR and watt meter I can confirm this output, am I to connect my dummy load to the SWR meter and then SWR to CB?

Thanks
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Re: Ticking an old box (Commtron box~)

Post by ChubbyChops »

You don't need a swr meter if you have a dummy load.
Just put the dummy load in the ant socket on the power meter and radio to the other one.
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Re: Ticking an old box (Commtron box~)

Post by un-realistic »

But how then would I prove the true TX power output i.e. that the meters own signal indicator is correctly displaying power and doesn't need calibrated.

If in fact I am only producing 1+ W TX - where do I start diagnosing the cause?
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Re: Ticking an old box (Commtron box~)

Post by ChubbyChops »

You need an accurate power meter.
Don't believe the built in signal meter.
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Re: Ticking an old box (Commtron box~)

Post by Buick Mackane »

Dummy load & a decent quality power meter, The radio might just need the TX Stages aligned, But keep in mind that not every 27/81 radio is capable of producing the full 4 watt legal limit.
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Otter
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Re: Ticking an old box (Commtron box~)

Post by Otter »

un-realistic wrote: 15 Feb 2022, 23:52 where do I start diagnosing the cause?
I'd look at the output transistor and see whether it's the correct one for the radio. If it looks like it may have been replaced, try to work out whether the transistor is a genuine one.
"To this day the words Stirling bridge conjour pride in every Scotsman's heart, while to an Englishman those same words conjour literally no feelings at all." - Cunk on Britain S1 E1
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