That is what I was sort of thinking would happen. Most of the
responses to my question are useful, but as usual you can't post
to this list without someone calling you stupid.
Gee- at least I am doing some building unlike most hams.
I did not consider the fact that I was actually pushing the diodes.
The reason I am running several in series is because the amp is a pair of
Russian GI7 triodes and needs more bias than usual ~30volts
or so. Sounds like I need to go with the xsistor/zener. Or a big zener.
Doug
dan hearn wrote:
> Unfortunately the branch which has the lower total zener voltage will
> take most of the current so that is not a good idea. Fortunately, there
> is a good simple solution to your problem. A power transistor with a
> single zener and a resistor will make a good bias source. One I have
> used with an 8877 consists of a 2n3055 with an 8.2 volt zener from
> collector to base and a 47 ohm 2w resistor from base to emitter. The
> zener cathode goes to the collector. The emitter goes to gnd and the
> collector to the amp cathode. I have seen this design in several
> published amp circuits. Sometimes a power resistor 5K 20w is shunted
> across the transistor collector to base. I think this may be to protect
> the tube in case of failure of the bias circuit.
> 73, Dan, N5AR
>
> Douglas R Snowden wrote:
> >
> > I have an amp that I have put several 5.6Volt @ 5watt zeners
> > in series for cathode bias. They get way too hot with
> > about 800ma of current. Can I parallel zeners to divide the
> > current without problems with balance between them?
> >
> > Doug, N4IJ
> >
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