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Author Topic: Yaesu FT-450AT - Tired Finals?  (Read 137 times)

MM0IMC

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Yaesu FT-450AT - Tired Finals?
« on: July 28, 2022, 11:27:08 AM »

I've noticed that my 13 year old Yaesu FT-450AT seems to be putting out less power than it used to, so what used to be about 100W is now reading 75W-80W, depending on the band.  This is into a dummy load with a SWR/power meter that I've used for a long time.  There's no indication of a drop off of power on the rig's internal meter.

I've removed all accessory cables, just leaving the power lead and patch lead attached.  I've cleaned out any dust from the rig and checked any internal connection are secure.

I know that valves/tubes can lose emissions after a time, but I thought transistors usually just die quickly. :-\  Am I missing something?
« Last Edit: July 28, 2022, 11:30:40 AM by MM0IMC »
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W1VT

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Re: Yaesu FT-450AT - Tired Finals?
« Reply #1 on: July 28, 2022, 11:30:32 AM »

I would check the supply voltage at the radio with a quality voltmeter.  I just got a new Fluke meter for my station.

Zak W1VT
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MM0IMC

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Re: Yaesu FT-450AT - Tired Finals?
« Reply #2 on: July 28, 2022, 11:46:20 AM »

I would check the supply voltage at the radio with a quality voltmeter.  I just got a new Fluke meter for my station.

Zak W1VT

I get 14.2V DC at the power supply and the same at the end of the power cable.  The voltage drops to 13.5V DC inside the radio, when TX'ing at 100W CW.  The overcall current draw as indicated at the PSU is about 18 Amps.
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W1VT

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Re: Yaesu FT-450AT - Tired Finals?
« Reply #3 on: July 28, 2022, 12:09:34 PM »

If there is no drop off in power on the radio's meter and the external meter is reading lower, you may need another power meter to decide which one is right.

The radio's meter is connected to the meter's ALC circuit, so it may just be that the feedback circuit has drifted over all these years.
It may also be that the external meter has drifted.
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KB1GMX

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Re: Yaesu FT-450AT - Tired Finals?
« Reply #4 on: July 29, 2022, 04:52:36 AM »

Finals that are not tubes (valves) do not get "tired".
They can fail outright but that would not be a small decrease
and the TX audio would suffer badly.

Lower power usually means metering error, change in adjustments
(mic gain or drive) or power supply issues.  It can also be having
the antenna tuner operating while testing into a 50 ohm load.

With that 80W is less than 1db lower than rated 100W.  The guy
at the other end will not notice.

The whole exercise presumes that radio actually put out 100W
previously.

Allison
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KB1GMX

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Re: Yaesu FT-450AT - Tired Finals?
« Reply #5 on: July 29, 2022, 05:00:04 AM »

Additional...

Many radios have ALC circuits.  If that circuit has issues the power
out can change from normal to excess or less than expected.

There is sufficient complexity to say its possible something is wrong.

Or just  the meter used. Most power meters are 5% at full scale and
making the display system digital does not generally improve that.

The power meter should be tested against a known one to insure its
reading is accurate.



Allison
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WB6BYU

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Re: Yaesu FT-450AT - Tired Finals?
« Reply #6 on: July 29, 2022, 06:26:22 AM »

Are you taking the measurement with the built-in antenna tuner
enabled?  That will reduce your output power somewhat if you
are using an external meter, but the difference doesn't show on
the internal meter.

Also, make sure that your ALC / POWER OUTPUT knob is full
clockwise.

If you don't have enough drive power to activate the ALC, then
your radio may need alignment.


But, no, transistors don't decay over time the way valves do.
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