On a sunny day (25 Sep 2006 04:40:57 -0700) it happened "Telstar Electronics"
wrote in
.com:

Bill Gates wrote:
Why does every post griffey does end with LOL????'

Because I can't help but laugh at some of the stupid comments I read
out here. Bottom line... that circuit with those two little doides
isn't doing any temperature tracking for the bases of those
transistors. Several things are wrong:

1.) The bias that feeds those bases needs to be very low impedance...
on the order of around 5 Ohms. There is no freaking way that those
little diodes could carry enough bleeder current to feed those bases.

That lookes like 1A diodes, and would be no problem.

All you phantasies, your lack of a decent Pi filter, you failing
to grasp heat rises upwards (you can hold your hand next to a candle but
not above it), so diodes _above_ transistors is _good_, but I will show
you how the profies do it, this is what runs he
http://www.cbtricks.com/radios/rci/r...0_main_sch.gif
It is a big gif, go to bottom left corner, there is the amp, the Pi filter,
and the temp stabilaziation a bit to the right of that.
Oh, and the on board SWR meter (all teh way at the left).
And here is the amp PCB layout:
http://www.cbtricks.com/radios/rci/r...rf-amp_pcb.htm
It is only 150W PEP, but it works great here.
And no harmonics with that filter.

Oops, do I see 2 diodes in parallel? Must be me eyes ;-)
Oops it is 1N4001.
So now copy-cat the Pi filter?
Oh what, you have the whole diagram.

I have to point out that the Ranger 2970 is a nice set, clocked many
hundreds of hours here, not one problem.
Good sound quality too.

OK over to Telstar for the Telstar diagram, hey if Ranger publishes theirs,
what have you got to hide?
And they are making $$$$

Jan Panteltje wrote:
OK over to Telstar for the Telstar diagram, hey if Ranger publishes theirs,
what have you got to hide?
And they are making $$$$

That's Ranger's business... not to be confused with mine.

http://auctions.yahoo.com/i:SkyWave%...fier:117239910

"Bill Gates" wrote...

Why does every post griffey does end with LOL????

I do hope it's not catching... LOL.


Peter.

On Sun, 24 Sep 2006 21:59:32 -0700, Frank Gilliland wrote:

On Sun, 24 Sep 2006 23:30:24 -0400, "LeIand C. Scot"
wrote in :

snip
I'm sure somebody is going to nit-pick this post. They're welcomed.


Not picking nits, just taking a different approach.....

Thermal bias compensation works to a point but neglects one important
issue: it takes time for heat to travel from the junction to the
outside of the package, and thermal runaway can happen faster than a
-thermal- compensation circuit can respond to it.

Exactly. That's why those diodes are place on the ceramic cap of the
device and not on the heat sink.

Since the heat
buildup is due to excessive EC current, it makes more sense to control
the EC current directly.

There are two solutions that use this approach. One is to include a
resistor on the emitter with a TC opposite of the transistor. Not
precision but much faster response.

This is done in many audio amps. The chief problem is the negative
feedback introduced by the emitter resistor. At auto frequencies this
resistor is bypassed by a rather large electrolytic capacitor sized such
that at the lowest frequency of interest the reactance is much smaller
that the emitter resistor value. Thus the "AC" gain isn't affected much by
the emitter resistor.

Believe it or not I've seen many of the old Motorola RF devices use
internal emitter resistors. Those took the form of many small tungsten
bonding wires from different areas of the emitter structure to the emitter
terminal. The main idea there was the many wires, resistors, in parallel
resulted in a very small overall emitter resistor. Also they found that a
problem called "second break down" would occur if they didn't do this.
What it amounted too was local hot spots, thermal runaway, in tiny areas
of the transistor's emitter structure. I think the term they used for RF
devices built this way was "emitter ballasting".

The other is to monitor the EC
voltage and the base current; send both measurements to a differential
OP amp and use the output as feedback for the bias regulator.

You would have to look at the "DC" emitter current minus the "AC"
component, which I don't think is going to be so easy to do.

Regards,
Leland C. Scott
KC8LDO

Leland C. Scott wrote:
Exactly. That's why those diodes are place on the ceramic cap of the
device and not on the heat sink.

Having the sensing on top of the transistors is a poor location.
The internal die is in intimate contact with the heat sink... not the
top! The heat sink... preferably near the device is the proper location

for any tracking device.

http://auctions.yahoo.com/i:SkyWave%...fier:117239910

"Telstar Electronics" wrote in message
ups.com...
Leland C. Scott wrote:
Exactly. That's why those diodes are place on the ceramic cap of the
device and not on the heat sink.

Having the sensing on top of the transistors is a poor location.
The internal die is in intimate contact with the heat sink... not the
top! The heat sink... preferably near the device is the proper location

for any tracking device.

Are you really that dense?

On Mon, 25 Sep 2006 19:06:49 -0400, "Leland C. Scott"
wrote:

+++Believe it or not I've seen many of the old Motorola RF devices use
+++internal emitter resistors. Those took the form of many small tungsten
+++bonding wires from different areas of the emitter structure to the emitter
+++terminal. The main idea there was the many wires, resistors, in parallel
+++resulted in a very small overall emitter resistor. Also they found that a
+++problem called "second break down" would occur if they didn't do this.
+++What it amounted too was local hot spots, thermal runaway, in tiny areas
+++of the transistor's emitter structure. I think the term they used for RF
+++devices built this way was "emitter ballasting".
*********

I have never seen tungstun bonding wire. All I have ever seen is gold.
You need a soft malible metal to bond to the die pads on any
semicondcutor. The bond wire is sonic heated to the aluminum metal die
pad. This forms the nice ball on the die pad that is a weld of the
aluminum and gold. Tungstun is far to hard a metal for bonding.

Emmitter ballasting is done on the die within the emmitter matrix.
There are several metods of fabricating an RF transistor. Major
factors are power, frequency and device operating point. For most
transistors operating below 50 MHz use an interdigitated emmitter
geometry. Incorparated within are current balancing resistors in the
emmitter matrix. This does increase die size and reduces gain. It does
spread heat and current more evenly through the die. Interdigitated
emmitters will have multiple bond wires.

Peter wrote:
I do hope it's not catching... LOL.

It is... if you stick around and read some of the techno-babble on this
group... LOL

www.telstar-electronics.com

U-Know-Who wrote:
Are you really that dense?

Thanks for that great post... you really add a lot to any conversation.

www.telstar-electronics.com

LeIand C. Scot wrote:
Tacking the diodes on to the case of the transistor works better than
attaching them to the heat sink due to the relatively slow thermal response,
the heat sink changes temperature slower than the cap on the transistor.

That's simply not true... while the heat sinks response might be a bit
slower... it's a much better indicator of the temp of the transistor
die. The ceramic cap on those transistors will overshoot the die temp
in both directions because of it's poor thermal contact with the die.

www.telstar-electronics.com