[Amps] Need Zener for 2KD-3
Carl
km1h at jeremy.qozzy.com
Tue Feb 3 15:28:45 EST 2015
--------------------------------------------------
From: "Manfred Mornhinweg" <manfred at ludens.cl>
Sent: Tuesday, February 03, 2015 8:36 AM
To: <amps at contesting.com>
Subject: Re: [Amps] Need Zener for 2KD-3
> Bill,
>
>> I need a zener for my 2KD-3. It's a 1N4561. It appears that they are
>> really hard to find and exorbitantly expensive when you do.
>
> Power zeners are very much out of fashion. They have a tendency to burning
> out after some time, even when used perfectly within rated specs, and it
> seems that this made them impopular in new equipment.
>
> > Has anyone found a source for a replacement at a reasonable cost?
>
> My way to replace power zeners is to use a common low power zener together
> with a power transistor and a small resistor. The zener goes collector to
> base, the resistor base to emitter. The transistor is selected to
> comfortably handle the voltage, current and power, the zener is a low
> power unit (typically either 1 watt or 0.4 watt) with a voltage 0.6V lower
> than the original power zener, and the resistor's value is chosen to bias
> the small zener to about 10% of its maximum current, with 0.6V across the
> resistor.
>
> It's your choice whether to use an NPN or PNP transistor. If one side of
> the power zener goes to ground, it's often very convenient to select the
> transistor polarity so that its collector will be at ground. That way you
> can bolt it to the chassis for heatsinking, without needing any
> insulation. Of course you must connect the zener in the proper way,
> according to transistor polarity.
>
> This solution has a more stable voltage than a series string of diodes,
> uses fewer components, and doesn't need any extra support, because the two
> small parts are simply soldered to the transistor, which is bolted to the
> chassis or a heat sink. It's also suited to replace higher voltage zeners,
> which is impractical using diode strings.
>
> Manfred
Dentron did that as far back as the late production Clipperton L and there
were likely others prior. The 10-50W zener is a joke
Carl
KM1H
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