: From: Ron <w8ron@stratos.net>
: I did reduce the zero signal bias to about 3 amps before
: this all started and was concerned that the amp required
: such high bias to be stable and had caused my own
: problems.
-
Hi Ron,
-
You have to know that some bias circuit consume quite
a bit of power for a desired static device current. I have
one really nice circuit here that draws amps of current
at zero signal, but the device current is at the desired
mA level. You have to be able to separate out the actual
device current... The mfgrs rated static current for the
2SC2290 is only 50 mA per device.
An active circuit as found in the famous Motorola
bulletin and ARRL Handbooks consume much less
current than a practical current mirror bias circuit.
They're also a lot more involved...
-
: I would say that all of you comments indicate that
: is not the case and that 3 amps is about right.
-
I wouldn't be able to even guess without a copy of the
circuit diagram or a look at the circuit.
-
: There are two silicon diodes in the emitter circuit
: thermally coupled to each device and I suspect
: that it would stabilize the bias should one device
: get hotter than the other.
-
It's common to try and "track" the device bias circuit
to the temperature of the active device or the adjacent
mounting (heat sink). Sometimes you see diodes
on or in the metal (better) or across the top of the
device (not so good). Both active and current mirror
bias circuits can be made with similar type diodes
or a thermistor to keep a handle on the heat
problems. The best circuit is dynamic and adjusts
for heating.
-
: My first recall to the group was from memory in that
: I am writing during lunch and the rig is at home.
: The devices are 2sc2290 and are the same used
: in my FT-107. I don't have a service manual but do
: have a good schematic (with errors) that has been
: the only hints I get .
-
If you get me a copy of the diagram, I'll revise the
bias circuit with my tried and true circuit and send
it back to you to look at.
-
cheers
skipp
nospam4me@juno.com
-
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