[AMRadio] 813 tx


Jim candela jcandela at prodigy.net
Tue Oct 26 07:48:20 EDT 2004


Welcome Chris,

       I grew up in Detroit, Michigan where one day I discovered Ham radio
when tuning an old barn radio ( a Crosley) up past 1700 Khz until I reached
1806 Khz. Back around 1970 the Detroit area had several dozen hams on AM
using mostly home-brew gear on 160 where 1806 was the mobile frequency, and
1835 was the base frequency. The rigs back then were often low power, and
simple such as the two rigs on your web page. By the mid 70's 2 meter FM
took over, and the low power 160m rigs faded from the scene.
      I am curious about the non-licensed activity in Greece you refer too.
I wonder how organized it was, and since many had homemade tube rigs, I
suppose the topic of conversation was often about the equipment,
modifications, etc. I wonder if you can describe to the group how that went.
     Looking at your web page I see a rig using the EL-34 tube in a self
excited crystal oscillator. As you know this is a neat audio tube, and other
than myself you are the only person I've heard of using the EL-34 for RF
use. The EL-34 is inexpensive, readily available, has small diameter (like a
tall 6V6), and has beefy ratings. On the downside it has high interelectrode
capacitance (Cgp), and a fair amount of cathode lead inductance. These
characteristics may make it an excellent oscillator like what you have done.
In my case, being a masochist, I decided to use the EL-34 in a linear class
AB2 RF amplifier from 160-20 meters for amplification of AM / SSB signals.
This turned out to be a huge challenge for me. Along the way I noticed that
the 6550 was a better tube (more linear and stable) except that the 6550 was
too large, and had less gain. I also tried the 7591 with excellent results,
but the 7591 (NOS) is too rare and expensive. I continued on however with
the EL-34 determined and being bull headed until I achieved my objectives,
linearizing the EL-34 while maintaining stability. At the following link I
show an application of the EL-34 in use along with partial schematics.  I
did some more modifications to that rig, and the waveforms are a little
cleaner now. I was actually using a Svetlana EL-34 that cost US $12.00.

http://pages.prodigy.net/jcandela/CE20AQRO/20AQRO3.DOC

Regards, Jim Candela
WD5JKO
Austin, Texas



-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of CHRIS PAPAIOANNOU
Sent: Monday, October 25, 2004 10:45 PM
To: AMRadio at mailman.qth.net
Subject: [AMRadio] 813 tx


73 to all group's members around,
i'm new in this list.My name is Chris,my call is SV1DAF and i'm located in
Athens,Greece.
I'm not new in AM..20-25 years ago there was too much AM activity here,with
homemade tube rigs,in the MW band.Was illegal but there was.Then most of the
"amateurs"became hams with legal activity in the ham bands.The rest of them
left the radiowaves.
Not long ago i started homebrewing again after long time.My homebrew rigs
now are:
1)6V6/807 crystal controlled where the 1st tube is the oscillator tube and
the 2nd one the pa one.
2)6J5/EL34
I prefer plate modulation and the reasons are known and clear,and i'm using
an amp with 2 EL504s like output tubes.These are sweep tubes.
I'm now searching for a tx drawing with an 813 tube like pa tube.Any replies
will be too much appreciated.
Tnx for the attention paid to my introduction,
73,Chris,SV1DAF.
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