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.
2.) And if that's not enough... there is another fatal flaw with that
scheme. It's effectively paralleling diodes... the small diodes hanging
on top... and the diodes in the base-emitter junction of the power
transistors. Electronics 101 says that it's a bad plan to parallel
diodes (why you never just parallel bipolar transistors!). The
reason... because one will always hog the current... and starve the
other. One will be on... the other is cut off. You will never get them
both on at one time. Soooooo... when this happens... you can't get any
tracking... because only one diode is on at a time.
3.) 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 het sink... preferably near the device is the proper location
for any tracking device.

Like I said before... it's not quite that simple just tacking a couple
diodes on top of the devices... LOL

www.telstar-electronics.com

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

"Telstar Electronics" wrote in message
oups.com...
Like I said before... it's not quite that simple just tacking a couple
diodes on top of the devices... LOL

http://perso.orange.fr/f6itv/p2032001.htm (look at location of diodes in
photo at right side)


--
Regards,
Leland C. Scott
KC8LDO

LeIand C. Scot wrote:
http://perso.orange.fr/f6itv/p2032001.htm (look at location of diodes in
photo at right side)

Yes, this method is similar to a few "reference" designs shown in the
Motorola RF Data Manual . This is a poor method for two resaons. The
first is what I explained before... trying to get two diodes in
parallel to turn on together is very difficult... if not impossible on
a repeatable basis. Second, the emitters you are feeding with the DC
bias are very low impedance. This creates its own problem when
attempting to control the base current. This biasing scheme with temp
compensation is a "brute force" method that dissipates large amounts of
power... and plain doesn't work well. It's not the first time that
circuits shown in a reference manual are not production ready. Motorola
also shows a much better method of temp comp bias in that same data
manual. It uses an op amp and sink mounted thermistor. I'm also using
an "active" approach to the temp comp bias in my amplifier... but a
totally different circuit using a bipolar transistor as the sense and
gain mechanism. I can hold the 500mA bias to 10% from -30 to +85C.

www.telstar-electronics.com

On 26 Sep 2006 16:10:26 -0700, "Telstar Electronics"
wrote in
.com:

LeIand C. Scot wrote:
http://perso.orange.fr/f6itv/p2032001.htm (look at location of diodes in
photo at right side)

Yes, this method is similar to a few "reference" designs shown in the
Motorola RF Data Manual . This is a poor method for two resaons. The
first is what I explained before... trying to get two diodes in
parallel to turn on together is very difficult... if not impossible on
a repeatable basis.


In the link above the diodes are not in parallel at all. Look at the
schematic.

In the link you initially provided they are indeed in parallel, but
that doesn't mean they are intended to conduct equal currents. If that
were the case then they would have current equalizing resistors in
series with each diode. From what I can see in the picture, it's clear
that only one diode will be working at any given time: the hot one.
And I'm sure that's exactly what was intended.


Second, the emitters you are feeding with the DC
bias are very low impedance.


Very low voltage, too. Some might even call it a "ground potential".
The bases, on the other hand......


This creates its own problem when
attempting to control the base current. This biasing scheme with temp
compensation is a "brute force" method that dissipates large amounts of
power... and plain doesn't work well.


Apparently it works well enough for a homebrew amp.


It's not the first time that
circuits shown in a reference manual are not production ready.


Hey, look what I found on a quick google search:

================
On 31 Jul 2005 15:58:33 -0700, "Professor"
wrote in
.com:


Frank... I wish I was like you... never wrong... and never had to be
corrected.


Yes, I already knew that, Brian. I tried to turn you onto the right
path years ago when you were hacking basic Motorola AN circuits that
were intended to be starting designs for engineers, not finished
products to be built by CB ampheads. But you were just too impatient
to get your "product" sold and get your share of that illegal market.
After damage control backfired in your face (because of your lack of
education) you vanished. Now you pop back up to spam the group every
time you think you have an improvement. You haven't made very many
changes, but look at the ones you -did- make -- all were suggestions
that I made when I told you all the reasons your amp sucked. Maybe you
learned those things from me or maybe somewhere else, but I was right
and you know it......
================

So contrary to recent opinion polls, it's clear that you -can- learn
things. You just can't admit that you learned anything from someone
else because that might be bad for business.


Motorola
also shows a much better method of temp comp bias in that same data
manual. It uses an op amp and sink mounted thermistor. I'm also using
an "active" approach to the temp comp bias in my amplifier... but a
totally different circuit using a bipolar transistor as the sense and
gain mechanism. I can hold the 500mA bias to 10% from -30 to +85C.


Hey Jan, wanna know why Brian won't cut loose his schematic? Because
Brian is a hack and his special bias circuit was most likely ripped
from this link, which was posted in this group a couple years ago:

http://www.ifwtech.co.uk/g3sek/tr-bias/tr-bias1.htm

Frank Gilliland wrote:
Hey Jan, wanna know why Brian won't cut loose his schematic? Because
Brian is a hack and his special bias circuit was most likely ripped
from this link, which was posted in this group a couple years ago:

http://www.ifwtech.co.uk/g3sek/tr-bias/tr-bias1.htm

Yes Frank... look for an ally. Lord knows you need one... LOL

www.telstar-electronics.com

Frank Gilliland wrote:
http://www.ifwtech.co.uk/g3sek/tr-bias/tr-bias1.htm

Thanks Frank for posting this link. It supports what I've been saying
all along about the plain-old diode method working like crap. So why
don't you go ahead and use that method on your new amp... LOL

www.telstar-electronics.com

On 27 Sep 2006 03:05:16 -0700, "Telstar Electronics"
wrote in
om:

Frank Gilliland wrote:
http://www.ifwtech.co.uk/g3sek/tr-bias/tr-bias1.htm

Thanks Frank for posting this link.


No problem.


It supports what I've been saying
all along about the plain-old diode method working like crap.


The diode method works, it's just not idiot-proof so it's no good for
a production CB amp. So why didn't you incorporate the concept in your
earlier amps instead of vehemently defending your no-bias Class C POS
by claiming that "linearity is not required for SSB"?


So why
don't you go ahead and use that method on your new amp... LOL


Naw, I have a better system.

Frank Gilliland wrote:
The diode method works, it's just not idiot-proof so it's no good for
a production CB amp.

Well, I claim it doesn't work... unless you want to tell me how you can
parallel two diodes together... without any ballasting... and have both
of them turned on. That's essentially what that circuit is doing.
Unlike you... I have certainly tried it before. It doesn't work... for
the reason I stated.

http://search.ebay.com/_W0QQfgtpZ1QQ...Q2delectronics