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Re: [Yaesu] FT-1000D questions

To: <yaesu@contesting.com>
Subject: Re: [Yaesu] FT-1000D questions
From: "Tom McDermott" <tom.mcdermott4@verizon.net>
Date: Sat, 24 Jan 2004 10:38:55 -0600
List-post: <mailto:yaesu@contesting.com>
The keying transistor in the FT-1000MP is specified to handle 12 volts. The
Alpha amplifiers have about 24 volts on the key line. That said, I measured
the breakdown voltage of the transistor in my MP, and it's more than 50

I've run both 76PA and 87A amplifiers using the band data connector without
problems for at least 5 years. With the MP keying relay turned off it is
very nice.

The mechanism here is called 'avalanche breakdown'. When the transistor if
(not keying the amplifier) if the voltage applied to the transistor voltage
the avalanche voltage, it will conduct anyway, and usually fail due to
Avalanche itself does not cause the transistor to fail, it's the excess
power dissipation
that does it.

To measure the withstand-voltage, I used an old Heath capacitor checker with
a 1 megohm resistor
in series to the transistor (making sure not to accidentally reverse the
But you could use any variable DC supply with the right voltage capability.
A DMM across the resistor tells if the transistor is starting to conduct.
The resistor
limits the current to the transistor to a safe value should it decide to

Then the test voltage is increased up to about 50 volts while watching the
DMM. I quit
at 50 volts, deciding that was sufficient safety margin compared to the 24
volts presented
by the Alpha amplifier.

Incidentally, the avalanche voltage is temperature-dependent. At higher
temperatures, it
decreases, so run this test with the rig at maximum expected temperature, or
at room temperature to a higher test voltage.

        -- Tom, N5EG

John writes:

> I also noticed that the owner was switching his Alpha amp via the 'Tx GND'
> socket and associated relay. I'd have thought it should be possible to use
> pins 2 and 3 on the BAND DATA output to achieve the same end -- is this
> correct?

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