Re: BU406 vs. BU406D

For use in the high-voltage power supply section of the Ampifone monitors -
they are definitely not interchangeable, unless you have a background in
electronics...... please read on.

The "D" in BU406D represents the inclusion of a diode across the emittor
and collector inside the package. If you look at the Amplifone schematics,
the BU406D switches power across the primary coil of the high-voltage
transformer. When the power in the coil is switched off, the
electromagnetic field collapses, causing an opposite polarity voltage to be
induced in the primary coil. This voltage rises to the point where it can
arc across the transistor junction, thus destroying the transistor.

The intregal diode is a "safety valve". When the magnetic field collapses,
the diode allows this induced voltage to short across the diode, keeping
the reverse voltage level to around .6 - 1 volt rather than several hundred.

Keep in mind that this "safety valve" operates at the frequency of the
oscillator, at the rate of 10 thousand times per second. You can see how
the BU406 without the diode can be destroyed pretty quickly if the
conditions are right.

If you understand power supplies, and have access to "turn on" time data
for diodes, then you can use the BU406 and add an external fast diode to
replace the BU406D. However, if you are not confortable doing this, or do
not have access to and understand this data, THEN ONLY USE THE BU406D
!!!!!!!!!!!!!!!!

I replaced a faulty BU406D in my Star Wars with a generic BU406
replacement, and used an external diode to complete the fix. Mine has been
working fine for almost a year now with 3 months "on location" with no
problems. I'm also using the Wintron replacement transformer.

Again, unless you fully understand the implications of using an external
diode, then use the BU406D. You can use an external diode, but you'd better
know what you are doing or you are gonna fry the high voltage transformer
AND the transistor!

        - Matthew Sell

P.S. Again - The "D" in BU406D represents an intregal diode, not a later or
better revision of the BU406 transistor....

At 07:31 AM 3/6/00 -0800, you wrote:
>After last week's postings on the BU406D, I stopped by Radio Shack and
>ordered a few from RSU. First, they are not the D's. They are shipping
>the BU406. Second, are the 406 and the 406D interchangeable? I seem to
>remember they're not, but I couldn't find the specs to compare them both.
>Thanks.
>
>Steve
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Received on Mon Mar 6 11:40:18 2000