[Alejandro Lieber[_3_]]

Patrick Turner wrote:
On Friday, 12 October 2012 01:44:25 UTC+11, Alejandro Lieber wrote:
Patrick Turner wrote: On Wednesday, 10 October 2012 18:48:54 UTC+11,
John L Stewart wrote: 'Alejandro Lieber[_3_ Wrote: ;963267']I am
thinking in building an AM transmitter for 7.1 Mhz (40 meters)
using a EL34 in class C as final. The idea is to modulate it by
varying the negative polarity of the suppressor grid (g3).
Suppose I load the EL34 plate with 500 volts DC and a current of 150
ma with 0 volts suppressor, does anyone have any idea what
negative voltage in g3 is needed to reduce the anode current by
half, needed for screen AM modulation ?. Alejandro Lieber
LU1FCR Rosario Argentina Real-Time F2-Layer Critical Frequency
Map: http://1fcr.com.ar --- news://freenews.netfront.net/ -
complaints: --- As the G3 voltage is biased
negative the G2 current will increase in proportion to the decrease
in anode current. That can result in a dangerous increase in screen
dissapation. To prevent that, the screen needs to be supplied thru a
limiting resistance. Refer to the attachment lifted from FE Terman.
The EL34 will easily handle your 500 volt supply, it is rated to 800
volts on the plate. But the socket is something needs to be of good
insulation. As Patrick T has said, an 807 would be a better choice.
Many amatuer transmitters were built using TV horizontal output
tubes which are still common. That gets around the socket insulation
problem. And it better isolates the RF input circuits from the
output. Less likely to have parasitic oscillations. Cheers, John
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-- John L Stewart Amateurs I have known used to use 807 mainly
for all their RF amps and AF modulators because they were cheap from
Army disposal stores and had better insulation for anode connections.
But one ham said that a pair of EL36/6CM5 ( TV line output )could
make 300Watts in class C. Other octal line outputs with anode top
caps were 6DQ6 and 6CD6. Then there was the 6146 which many hams
used. My first ham transmitter (1969) used only two valves: a EL36 from
an old TV set and a 6V6. The EL36 was a crystal controlled (3.640 Mhz)
oscillator with 10 watts output, plate modulated by the 6V6 with a
reactor. The microphone was an old carbon telephone one with the DC
current taken from the cathode of the 6V6, and a 3.2 ohm to 10.000 ohm
small transformer as voltage amplifier. No power transformer, 300 V DC
directly from the 220 V AC line. I made hundreds of contacts up to 700
km. Much more fun than what I get now with my commercial Single Side
Band rig. ........ Patrick Turner. -- Alejandro Lieber LU1FCR
Rosario Argentina Real-Time F2-Layer Critical Frequency Map:
http://1fcr.com.ar --- news://freenews.netfront.net/ - complaints:
---

I remember lots of ppl were into ham radio. But during these last years,
whenever I have tuned in to someone, he was usually older than me, maybe
80, and spending the whole time talking about his latest hospital
operation, droning on and on and on, and ppl were expected to wait until
he'd finished, then someone else would give a big long lecture about his
medical conditions. It seemed to me ham radio wasn't about really
connecting to other men for a useful reason, but was about being a
technical nerd and narcissist. I can tell you this mode of human
existance suits many blokes who are very ill at ease when having any real
deep and meaningful personal interactions with anyone else. Maybe WW2
****ed them up pretty bad. Besides, ham radio offers a chance to escape
the missus and kids while you spent 20 years in suburbia raising a family
after 1 month's bliss with a young missus, then 30 years waiting to die.
The ham radio shed was no place for the missus or kids, or maybe even
grand kids, so often very full of cigarette smoke from the chain smoking
ham, who ignored his health conditions, and expected doctors to do
miracles. I think I found out early the basic trouble with ham radio is
that its like listening to Castro giving a 3 hour lecture on wonderful
socialism on Cuban radio, and sure, nothing wrong with socialism yet soon
after it is implemented all human progress is stunted and most humans die
of boredom and frustration. Mind you, listening to Romney is alarming,
worse than Castro. Just as well these silly old dinosaurs didn't get into
ham radio, they'd be able to drone on for hours about how they ****ed
everything up, or how they were about to **** everything up, while never
ever admitting how they were ****ing things up right now.

But yeah, 6CM5 plus a 6V6 and telephone mic probably could sound good and
go far. Just like you need a horn speaker with a 9 watt AF amp, you need
a good antenna for 9 watts of RF. I helped a few hams erect huge rotating
beam antennas above their houses. Some had elements that overhung the
house. Neighbours were always appalled seeing these things going up on
the house next door, and they complained about TVI and RFI even when the
ham wasn't transmitting.

As I mentioned in a previous post, my friend in 1962 had an 800Watt
transmitter with 2 x 813 outputs. He operated as a ham for many years, a
rare young man although very much a young nerd - but who had handsome
features so he was a hit with the girls, and once he quite casually stole
a GF from me. But having a motorcycle before I could get one was a huge
boost to getting pussy. Of course I soon realised she was just another
air-head deadbeat tart, and very hard to get along with like most other
shielas at the time who were so often wild and bored and unable to settle
down, or able to cook or even do a good BJ. Anyway, my friend had this
weatherboard shed with flat corrugated iron roof. The iron and boards and
door and one window were then probably 50 years old and all been taken
from a small cottage that had been demolished nearby maybe in 1958. But
this iron had spent its life under gum trees and settling leaves had
taken their toll on the zinc. My friend's old man was a bank manager and
extremely tight with money, so getting new iron was out of the question.
So once the old iron was very worn and disturbed and re-used in yet
another damn flat roof under overhanging trees it quickly gathered leaves
and leaked a lot, and there wasn't any silicone in them days and the
friend constantly battled leaks and dampness in the shed. Of course the
friend wasn't too law abiding, and operated as a pirate ham by addopting
the call sign of someone local who'd died about 5 years before,
sufficiently long ago for most ppl to have completely forgotten he
existed. But one day my friend said somebody was returning his CQ, and
said "Ah John, good to hear you are back on air again, someone said you
had died..." and my friend had to be diplomatic and make up a story then
and there, and then say dinner was ready and the missus was calling out,
so "over and out..." My friend didn't want to learn morse code, an
essential requirement to get a ham radio license. This regulation stopped
hundreds of people who would have liked to become a ham radio enthusiast.
Governments acted as Giant Kill Joy departments in 1960. My friend's
ex-army radio set transmissions attracted the attention of the PMG, Post
Master General or post office department which also regulated and
controlled all radio and TV transmissions. My friend worked as a
telephone linesman in the PMG after leaving school earlier than me, and
he knew about how other sections worked, and about their radio detection
van which drove around to find illegal radio transmissions. Well, one day
while transmitter was on, he watched the van drive right past his house.
He was using the shed roof iron as antenna, about 3 metres x 4 metres,
flat. Electronically, it was very poor, but with such high power the RF
still went far. I recall the antenna lead from Xmitter just went out the
door with large aligator clip to roofing iron, and a light globe was used
to see if it was tuned right. Later he spoke to blokes in the van, and
they said they'd "detected a very powerful signal in Warrangi St, but we
couldn't get a proper fix on it and we couldn't see any antenna.." My
friend knew his set overloaded their gear. He could hardly keep a
straight face. Patrick Turner.

Patric:
I am an electronic engineer. Studied here in my town, Rosario, Argentina.
Being a ham helped me a lot while studying. But in the last 20 years, I have
talked to the microphone no more than 20 hours. I mostly tune to 7 Mhz, the
last band where some hams can be found, most from no more than 500 km,
mostly from places I have visited during my life. I like to hear hams
talking while I work on the computer. I rarely talk to them, mostly because
the useful time one looses.

--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map:
http://1fcr.com.ar

--- news://freenews.netfront.net/ - complaints: ---