[Amps] Zener Diodes

[Paul Baldock]

The easiest and most reliable solution is to put a number of silicon 
diodes in series. For 8V you would need about 13 diodes. Probably 
1N4007 would do the job at around 2 cents each.

- Paul

At 03:22 PM 5/28/2017, you wrote:
>Mike needed this as a replacement cathode bias diode in an old
>homebrew 8877 amp with 2600V on the plate.  Manfred's suggestion is
>the more contemporary solution, but in any case a 50W zener is way
>overkill. A 10W zener would work just fine, and these are still
>available without spending a fortune.
>73,
>Jim w8zr
>
>Sent from my iPad
>
> > On May 28, 2017, at 4:01 PM, Ron Youvan <ka4inm at gmail.com> wrote:
> >
> >>  On 05/28/2017 12:35 PM, Manfred Mornhinweg wrote:
> >>
> >> Mike,
> >
> >>> I need to know where to get a 8 volt 50 watt stud mount Zener 
> diode 1n3303
> >
> >> Such 50W Zener diodes seem to have fallen out of favor with 
> designers, because of their poor reliability. I have seen lots of 
> them fail, in various applications. I wonder if any company is even 
> making them anymore.
> >
> >> If you can't find some old stock, probably your best option is 
> to use a common small (1W) Zener connected between collector and 
> base of a suitable power transistor. Add a resistor (anything 
> between about 47 and 68 ohm) from base to emitter, to bias the 
> Zener into its plateau.
> >
> >> You can use either an NPN or PNP power transistor. I choose 
> between them   depending on which side of my Zener replacement I 
> want to ground or attach to the heatsink. For a Zener replacement 
> having the negative end attached to a grounded heatsink you want a 
> PNP transistor.
> >
> >> TIP35 and TIP36 transistors are cheap, widely available, and typically
> >
> >  The TIP120 and TIP125 will each dissipate 65 Watts if properly heat
> > sunk and they are Darlington type with a dc gain of approaching 1,000.
> >
> >> work well in this circuit, but their gain is a little on the low 
> side, so they might overtax a small Zener if the load current is 
> high. The 2SC5200 and 2SA1943, available from Digikey, seem better 
> choices, but I haven't yet used them. Same thing for the FJA4213 and FJA4313.
> >
> >> The Zener used should have a nominal voltage roughly 0.6V lower 
> than the actual voltage you need.
> >
> >> Such a transistor + small Zener + resistor combination costs far 
> less than a 50W Zener, if you can find one, and in my experience is 
> more reliable.
> > --
> >  Ron  KA4INM - Youvan's corollary:
> >                Every action results in unwanted side effects.
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