Homebrew TX

Jan 3 2004

As seen here, the rig was still under construction!

The power supply uses a mains transformer from an old Bogen
P.A. amplifier. Yes, rusty but I might paint it some pretty color, ha!
The full wave diode rectifier provides it with an unloaded B+ voltage
of about 525V. Under load it drops to about 505V - not bad.

I am using a 6CL6 pentode as a Colpitts crystal oscillator with untuned
output. In other words it has an RF choke in the plate circuit
and is coupled capacitively to the 2E26 grid.
On the 6CL6 there is 220V of B+ and 120V of screen voltage.
I had to use some subs, like a 40 pF and a 330 pF instead of
a 22 pF and 220 pF on the grid. But what the heck!

I plan to convert this TX to grid block keying eventually.
Right now it just has the cathodes temporarily grounded for
testing purposes, so if I turn it on it is ON, period!

Thanks to QUARTSLAB in England for some of the experimental crystals
I am using.

Homebrew TX

Jan 4 2003

I plan to post the complete schematic diagram and other
details about this rig on this web site.

In spite of my use of many substitute parts - the rig has
lived up to my expectations and I now have RF emanating
from the 6CL6 oscillator and I can tune the final.

I plugged in a 7225 kc. rock and hauled her upstairs to the shack,
tuned the receiver to 7225, and lo and behold I have a strong,
clean signal!

Homebrew TX

Jan 4 2003

You can see the changeover relay here - it was not wired up yet.
I have since added: 1) Front panel T-R switch to turn on the B+ (Grid block bias stays on)
plus change the antenna over all in one.
2) Grid-block keying.


Jan 5, 2004
I am now ready to go for it this evening on 7029 kHz
and 7049 kHz so I hope all of you other enthusiasts are
going to be listening for me tonight and every night on
those two frequencies. I may be on in the mornings too,
so please listen around 0900 to 1300 UTC also!

How about some of you brave VK and ZL chaps taking a listen for me?

Jan 6, 2004

I am noticing a couple of intermittents here. Sigh...
The rig went into a strange mode yesterday where it would not
load properly. I turned it off for a few hours and played with
all of the tank area connections and coax cabling, and after that
it worked fine again. The symptoms were - loss of power out;
It dropped from about 25 watts down to about 5 watts out, and
would not load properly. That is: increasing the loading on
the output cap of the PI network would not cause any increase
in plate current as would normally be expected.
It's doing much better today. I just worked Phoenix, AZ with
a solid RST 579 each way!

There also appeared to be a temporary new problem when I switched
to using another rock on 7032 kcs. where it will suddenly jump
frequency by a couple hundred Hertz. Now it started behaving right.
Oh well! When I tapped on the chassis it jumped back
again, so maybe I have another loose connection or possibly even
a misbehaving crystal. I will post further observations.

Meanwhile back to making contacts, hi hi!

February 2004

Here you see the 'finished' rig for now with the plate current meter added.
It's a Weston 100 mA meter with a 1 ohm shunt to read from zero to 200 mA
There is also a 0.0033 uF at 500V DC mica bypass capacitor across the meter
to keep RF energy out of it.
There is no magic to the value of 0.0033 uF. These capacitors were what
I had on hand. You could just as easily use 0.01 or .002 uF caps.



Meter is not shown, but it is a 0-100 mA DC meter inserted in the plate
circuit to monitor current. There is a 1 ohm resistor in parallel
with this meter, and it also has a 0.003 uF bypass capacitor across
the terminals in parallel with the shunt resistor. The true scale is now 0-200 mA so all readings are doubled.

Voltage measurements

I took these measurements because something has been intermittently
changing so that the power out drops to about 20% of normal
and the plate current goes high. Normal plate current under load
is about 40 mA. When it is acting up, the load cap has to be at the
maximum (fully meshed) setting and the plate current is still about
60 mA which is not right. Since I can't readily make the problem come
and go I set up this chart to refer back to when it is acting up:

(Remember this is an older transfoermer from a 1940s-era
Bogen audio amplifier! Back then the AC line voltage was usually
around 110V AC, inlike today's 120 to 125V AC found in most homes.)

AC Filament voltage = 6.6V AC
High voltage secondary, no load = 772V CT
DC Voltage HT (B+), no load = 495V DC
DC Voltage HT (B+), full load = 462V DC

6CL6 plate, no load = 225V DC
6CL6 plate, full load = 216V DC

6CL6 Screen, no load = 133V DC
6CL6 Screen, full load = 127V DC

2E26 plate, no load = 495V DC
2E26 plate, full load = 462V DC

2E26 screen, no load = 490V DC
2E26 screen, full load = 136V DC

6CL6 Data Sheet in PDF format

6CL6 mini data sheet GIF

2E26 Data Sheet in GIF format

2E26 Full Data Sheet in PDF Format


Future plans include -
1) Pilot light.
2) Solid state conrol of the grid-block keying so
I can use an electronic keyer if desired. DONE
3) VFO - or DDS VFO for full coverage.
4) Screen grid modulation with a 12AX7 and 6DE7
a-la Heathkit DX-60, Cheyenne etc.

Of course the most exciting part is just getting it on the
air now and making some contacts.

On January 5th I made the first QSO on 7049 kHz CW
(Using my 7050 rock) with AF4FW in North Carolina.
Congratulations, Warren, and thank you for listening
to me through the annoying Spanish SSB "Slop Bucket" QRM!


Stations contacted so far:

AF4FW = Warren in Murphy, NC
K8BHG = Lee in Bluefield, WV
K4JEJ = Luke in Jupiter, FL
W5TVW = Sandy in Hammond, LA
K5DOA = Darwin in Hockley, TX
KJ5CR = John in Bryan, TX
W8DIZ = Diz in Cincinnatti, OH
W0MFQ = Tom in St. Charles, MO
K9LIR = John in Marion, IN
K1OPQ = dave in New Hampshire
K8ORD/7 = Ken near Phoenix, AZ
K5BQ = Dale in Ponder, TX
KB8ANY/M = Paul in Cincinatti, OH
K4CA = Paul in Madison, AL
WB4RDH = Rick in Moreland, GA

OK - I think I am almost finished adding any more of
these loggings, he he!


Read AF4K's early experiences with electronics and radio



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