Steveo wrote:
Are FET's the most economical transistors, or are are there other choices
for a 10 meter portable amp? The high drive would make it a bit more legal
too, wouldn't it? (dunno, just curious)

FETs like the MRF173 (or similar) have certain advantages. They also
have several disadvantages... one is cost! Franks proposed design
already looks to have a hefty price tag as described.

www.telstar-electronics.com

On 20 Sep 2006 02:53:13 -0700, "Telstar Electronics"
wrote in
om:


Frank Gilliland wrote:
No PCB = no cracked traces, copper seperation, no burnt boards, better
heat dissipation, more efficient conductors, etc, etc. Let's face it:
replace the power transistors more than twice on a PCB and your board
(and therfore your amp) is garbage. Not only that, but it also allows
the flexibility to use transistors of different physical sizes and
styles; i.e, the amp can be upgraded or retrofit as desired.

You're losin' it... no PCB at RF frequencies means wires and
uncontrolled inductances / resonances all over the place causing
instabilities... resulting in oscillations. Why don't you think any
commercial amps are built your way.
Great idea Frank... LOL... you're truly a great engineer!


How do you think amps and transmitters were built before the PCB was
invented? In fact, how do you think most broadcast transmitters (many
of which are still in use today) were built? By mounting a 4CX5000 on
a PCB? Why do you think the old chassis-wired Heathkits command a much
higher price than the later versions with more features but built with
PC boards? And did you know that UHF transmitters also existed long
before PC boards, were also constructed with point-to-point wiring,
and worked without the problems you claim are inevitable.... on HF?

I can cite dozens of examples of power equipment, both audio and
radio, that have histories of failure due to the use of PC boards
instead of hard wiring. I think Peavey is about the worst offender in
that department, in my own personal experience.

So you can fabricate any unfounded fear-tactic you like, the fact is
that PC boards (including the newer epoxy boards) just aren't adequate
for any high-power applications, let alone RF power applications. And
point-to-point wiring is a time-tested method that only seems to cause
problems for those who need a computer to tell them how to route the
wiring.

On 20 Sep 2006 04:28:52 -0700, "Telstar Electronics"
wrote in
.com:

Steveo wrote:
Are FET's the most economical transistors, or are are there other choices
for a 10 meter portable amp? The high drive would make it a bit more legal
too, wouldn't it? (dunno, just curious)

FETs like the MRF173 (or similar) have certain advantages. They also
have several disadvantages... one is cost! Franks proposed design
already looks to have a hefty price tag as described.


That's because I don't make cheap, disposable crap. Never have, never
will. But the use of FET's is at the discretion of the builder. The
amp can be built with either FET's or bipolars. No other modifications
are necessary, just a variation in the initial alignment.

On a sunny day (20 Sep 2006 04:28:52 -0700) it happened "Telstar Electronics"
wrote in
.com:

Steveo wrote:
Are FET's the most economical transistors, or are are there other choices
for a 10 meter portable amp? The high drive would make it a bit more legal
too, wouldn't it? (dunno, just curious)

FETs like the MRF173 (or similar) have certain advantages. They also
have several disadvantages... one is cost! Franks proposed design
already looks to have a hefty price tag as described.

www.telstar-electronics.com

http://www.sphere.bc.ca/test/rf-semis.html

On a sunny day (20 Sep 2006 02:53:13 -0700) it happened "Telstar Electronics"
wrote in
om:


Frank Gilliland wrote:
No PCB = no cracked traces, copper seperation, no burnt boards, better
heat dissipation, more efficient conductors, etc, etc. Let's face it:
replace the power transistors more than twice on a PCB and your board
(and therfore your amp) is garbage. Not only that, but it also allows
the flexibility to use transistors of different physical sizes and
styles; i.e, the amp can be upgraded or retrofit as desired.

You're losin' it... no PCB at RF frequencies means wires and
uncontrolled inductances / resonances all over the place causing
instabilities... resulting in oscillations. Why don't you think any
commercial amps are built your way.
Great idea Frank... LOL... you're truly a great engineer!

www.telstar-electronics.com

Well, not exactly, I had in the long ago past a nice 40MHz army transceiver,
toobes!!! (called '32set' IIRC) 40 MHz FM full of toobes and no PCB anywhere.
My own 500W linear PEP with toobe had no PCB either.
If you go to a real shortwave station, 10kW and up, they use big plumbing,
big toobes sometimes... (these days transistors too in modules OK).
PCB (an as already mentioned by somebody): the thickness of PCB traces becomes
a BIG issue especially if you run 1kW at 12V, a few milli-ohm will give
you big i^2 x R losses.
So copper strip is better anyways, lower current, and higher voltages, FETS,
means lower losses, you will need the switch-mode to get the higher voltage.
Switch-mode design 50V many amps is an art in itself, I have done switchmode
design for a company, it will take you study and time, and likely a few
transistor failures.

Soldering copper strips to these transistors will require you to support these
with proper spacers, so as not to mechanically load the transistors too much.
Else vibrations will rip the connections right of over time.

I like Franks idea, it is a lot like this one:
http://www.ibelings.com/n4ip/mrf157.html
I looked up the price of those FETS, 475$ each :-)
But I also found a pair on offer for less then 60$, was already gone however.
http://www.sphere.bc.ca/test/rf-semis.html
other interesting stuff there too:-)
In my school days I used to sell Motorola parts...... to finance my hobby.


So, anyways, long before the kids had PeeSeeBees the big boys were using
copper [wiring], and it did not [always] oscillate.
And in the old toobe times the voltages were more 'electrifying' too, mine
ran on 1kV, some used much higher voltage power supplies, dangerous these big
capacitors.
So the Telstar amp is just a small toy..... compared to what was done already
in and just after WW2.

But do not let that put you off, it looks like a nice amp.
And Frank will still have to build his ;-)


BTW you Americans have 110V, I had some BUZ44A (IIRC) MOSFETS that can do
500V DC, these oscillated (unwanted) around 20MHz, one could just plug it in
for a base station.... No voltage converter needed, not even a transformer.
Not sure if something like BUZ44A can be used as an amp.... at 27MHz.
http://www.datasheetarchive.com/data...rticle=1048164
probably to much input capacitance 1600 pF.....

But looking around for a nice FET may be worth it.

Frank Gilliland wrote:
That's because I don't make cheap, disposable crap. Never have, never
will. But the use of FET's is at the discretion of the builder. The
amp can be built with either FET's or bipolars. No other modifications
are necessary, just a variation in the initial alignment.

Let me get this straight...swapping FETs with bi-polars in the
design... and no modifications are necessary???
Get real... there are impedance matching issues, possibly B+ sources
level differences, as well as well as totally different biasing
circuitry. You are going to bias Frank?... right?

www.telstar-electronics.com

On Tue, 19 Sep 2006 14:31:52 -0700, Frank Gilliland
wrote:

+++
+++Enough of that cheap one-board crap..... this amp is MODULAR!
+++
+++Modular design allows easy repair and modification, as well as ease of
+++construction and interchangeability between different amps. It also
+++allows seperation of functions both electronically and physically. The
+++modules include:
+++
+++* Input module. Includes variable attenuator and dummy load which
+++provides adjustment of input power without 'tweaking' anything inside
+++the radio.
+++
*************

An attenuator on the input is nice. I am not sure a variable one is
needed. By variable a multistep attenuator with four to six different
values of attenuation would be a sufficient. A capability to switch
the input drive to a internal du mmy load would nice luxury item but
not necessary.

+++* Control module. Board that controls keying, bias & cooling fan.
+++
+++* Sensor module. Board with circuits that take measurements from
+++various locations throughout the amp and sends them to a meter. Meter
+++function selection can be by rotory switch or by LCD display simply by
+++swapping the board (module). Meter functions may include:
+++
*****************

Man talk about monitoring circuits. Nice thing to have on a high tier
amp. In reality most of these are great for development and early
testing. Actual production would cause product cost to sky rocket.


+++ - RF input power, Fwd
+++ - RF input power, Ref (for matching amp input to radio output)
************

Redundant circuitry since most modern tranceivers todday have some
form a SWR bridge incorparated into the transmitter. Would be more
needed if the run of coax from the transceiver to the amp were rather
long.

+++ - Base current
****************

If you are into monitoring everything, I would add a monitor of base
bias voltage also.

+++ - Emitter voltage, (RMS)
+++ - Emitter voltage, (peak)
+++ - Emitter current
+++ - RF output power, Fwd (RMS)
+++ - RF output power, Fwd (Peak)
+++ - RF output power, Fwd (Peak & hold)
+++ - RF output power, Ref
+++ - AF input (Ext. mod. function, AM only, see below)
+++ - DC supply voltage, amp
+++ - DC supply voltage, radio
+++ - DC supply current, amp
+++ - DC supply current, radio
+++
+++* Power Amplifier Module. The module will consist of the amplifier
+++circuit, heat sink and cooling fan, constructed inside an enclosed
+++sub-chassis designed for forced-air cooling. Flying in the face of
+++convention, the power amplifier circuit will -not- be mounted on a PC
+++board. Instead, the components will be chassis-wired with heavy-guage
+++copper, except for the transistors which will be wired with strips of
+++copper sheet having rounded edges and corners. This allows easy repair
+++and modification, as well as more secure and robust connections.
+++Circuit will be an ultra-linear, broadband, AB push-pull design
+++(details at a later date).
+++
****************

AIr dielectric striplines are nice for the power transistors. They do
introduce some memchanical issues. Great if you are in the 2KW or more
output range. In the 100 to 250 watt range 2 ounce copper laminate
would be quite sufficient. If varying dielectric constants are an
issue then a use of teflon laminate would be preferable over that of
FR4/FR5 laminates. Even alumina ceramics would offer a more stable
dielectrtic for the striplines.

Most of the low level, low current components do not require "dead
bug" style mounting. Laminates will do nicely. If you really want to
go whole hog on the striplines then why not take the copper strips and
either silver or gold plate them. Word of caution on gold over copper.
Nickel is not a good conductor of RF. Nickel is usually plated onto
copper to give gold a hard surface to plate to. Plating gold directly
onto copper requires a much thicker plating so that the copper will
not leach through the gold.

+++* Output module. Includes matching network and output connector, the
+++type of which depends on the desired output method: balanced or
+++unbalanced. The reason is that an unbalanced output is fine for mobile
+++amps where the amp is mounted to an adequate RF ground, but that is
+++rarely the case with base amps. So an option is provided for balanced
+++output; the line can then be run to a point where a good RF ground can
+++be found (e.g, a ground rod right outside the window) where it is
+++coupled to a coax with a balun, or simply run balanced right to the
+++antenna. The user now has these choices and they are built right into
+++the amp!
+++
+++* Power supply module (optional). Power transistors that are designed
+++for higher voltage are more linear and -much- more reliable than those
+++designed to operate on 12-14 volts. This switching power supply bumps
+++up the voltage to 28 or 50 VDC and allows the use of such transistors.
+++
+++
+++Additional features:
+++
+++* An external modulation function can be included, allowing the amp to
+++function as a Class C modulator. Audio input is via a terminal strip
+++on the back and fed from a common 8-ohm audio amplifier. The base bias
+++is then adjusted (with a screwdriver through a hole in front panel) to
+++Class C operation for higher efficiency. This works only in AM mode.
+++There is no provision for audio filtering, so hi-fi (wideband) AM is
+++possible if desired.
+++
*********************

Man after designing such a high tier amp, you adjust the bias through
a panel hole with a screwdriver? Will you supply the gold plated
screwdriver? I can understand why no band limiting filter designed in
since most CBers would bypass that anyway. Th en again, ,a hightier
amp as this would be nice to include it to show CBers what a nice
thing to hear band limited audio on the desired channel and not 20
channels away.


+++* Connections for remote operation:
+++ - Key ground
+++ - Key on ground
+++ - Key on high (=+5VDC)
+++ - Key function select 1 (amp in/out)
+++ - Key function select 2 (key auto/manual)
+++ - Key function select 3 (AM/SSB)
+++
+++
+++I am open to any comments or suggestions, provided they are limited in
+++scope to the design concept and desired features.
+++
+++
+++
***********

Oh well what the heck

james

On 20 Sep 2006 02:53:13 -0700, "Telstar Electronics"
wrote:

+++
+++Frank Gilliland wrote:
+++ No PCB = no cracked traces, copper seperation, no burnt boards, better
+++ heat dissipation, more efficient conductors, etc, etc. Let's face it:
+++ replace the power transistors more than twice on a PCB and your board
+++ (and therfore your amp) is garbage. Not only that, but it also allows
+++ the flexibility to use transistors of different physical sizes and
+++ styles; i.e, the amp can be upgraded or retrofit as desired.
+++
+++You're losin' it... no PCB at RF frequencies means wires and
+++uncontrolled inductances / resonances all over the place causing
+++instabilities... resulting in oscillations. Why don't you think any
+++commercial amps are built your way.
+++Great idea Frank... LOL... you're truly a great engineer!
+++
+++www.telstar-electronics.com
***************

Below about 1 KW, PCBs are adequate. In the 10 to 20KW range forget
laminates. You would have to plate at least 3 ounce if not 4 ounce
copper. Beisdes most laminates will have tremendous problems with RF
currents at these power levels. AIr dielectric or even ceramics
provide a better solution.

Also I believe Frank never mentioned the actual power out of his
design.

james

On Tue, 19 Sep 2006 18:41:35 -0700, Frank Gilliland
wrote:

+++On 20 Sep 2006 01:30:33 GMT, Steveo wrote in
:
+++
+++snip
+++Does the 25 watt -in- requirement make it anymore legal, or no? ( I really
+++don't know)
+++
+++
+++A ham could probably confirm this, but I think the minimum is 50 watts
+++input (with a license, of course..... without one it's no more legal
+++than having 5 watts input). Regarding -compliance- with the law, just
+++follow the leadership example set by our president and Congress.
+++
+++
**********

The FCC does not actually place a power limitation on the drive.
Instead the specifiy the maximum gain of the amp at 15dB. So with 2KW
output that would correspond to about 60 watt drive.

james

On 20 Sep 2006 04:28:52 -0700, "Telstar Electronics"
wrote:

+++Steveo wrote:
+++ Are FET's the most economical transistors, or are are there other choices
+++ for a 10 meter portable amp? The high drive would make it a bit more legal
+++ too, wouldn't it? (dunno, just curious)
+++
+++FETs like the MRF173 (or similar) have certain advantages. They also
+++have several disadvantages... one is cost! Franks proposed design
+++already looks to have a hefty price tag as described.
+++
+++www.telstar-electronics.com
**********

Prefer FETs even with their cost. They suffer less from thermal
runaway as bipolar designes do. Bias network is easier to design.

Major disadvantage to FETS are the inputs are very static sensitive.
SO some means of ESD protection is needed that wont h inder RF
performance.

james