[HomeBrew] "Rockin' Fifties MOPA"

[Philip Atchley]

Hi all,

Last night I started the construction of my little homebrewed "Glowbug" 
transmitter.  After looking around the web for suitable ideas to adapt to my 
own unit. In the "true" ham spirit (translated reads tight budget ;-) the 
goals of this project are to use entirely recycled parts, with no expenditure 
of funds, unless absolutely necessary.

Anyway, I settled on the 10 Watt one tube design (6T9) from the 1973 ARRL 
handbook, but substituting a 12AU7 and 6AQ5 for the tube, along with a 6X4 
rectifier.  I first prototyped the power supply using silicon diodes for the 
rectifiers.  The power transformer, chassis, tube sockets (even the 6AQ5 and 
6X4) are the same ones that was in the Eico signal tracer which "donated it's 
organs for this project.  I expected a little higher B+ voltage with silicon 
rectifiers, the no-load (same as Key-up) Voltage rose to somewhat over 400 
Volts, and it took a significant resistive load to bring it down.  WAY too 
much for a 6AQ5 final stage.

So, I decided to use the 6X4 rectifier, unloaded Voltage dropped to a more 
reasonable level.

THIS SET A NEW GOAL FOR THE PROJECT!  A transmitter based entirely on 
circuitry and components that a ham in the late '50s could be reasonably 
expected to build from parts secured from Junked radios (except for things 
like an Xtal socket, meter, relay etc).  Since the late '50s also saw the 
"birth" of Rock and Roll, and the transmitter is "rockbound" I coined the name 
"Rockin' Fifties MOPA".

But don't think that this is any "bare bones" transmitter that requires 
external antenna relays or anything.  The design I came up with includes 
antenna changeover via an internal 120VAC relay (So I don't need to use 
silicon rectifiers to provide DC for a relay), "Standby", "Spot", Tune and 
"Operate" switch (ala the Johnson Ranger) etc.

Anyway, construction is well underway and I hope to test the oscillator 
section this evening.  With only a couple "exceptions", everything in the rig 
will be vintage, right down to the recycled fastening hardware to avoid that 
shiny stainless look.  The tube sockets are better quality than came in the 
Eico (military ceramic for the final).  Here are the ONLY concessions to 
modern construction.

1.  A little bit of JB Weld was used to secure the Ceramic Xtal socket as I 
wanted to use an existing "oblong" hole and that was the only way to mount it 
(Don't think they had JB in the '50s).

2.  For the sake of reliability (and because I had them), a few modern 
"yellow" Poly capacitors are used rather than paper capacitors.  But I'm using 
ceramic disks wherever possible.

3.  Items yet to procure.  A 100mA meter and a 7040KC "rock" (I'll test it 
higher up in the band around 7200 where I have an Xtal).  A friend brought me 
a meter, but it's WAY too large and is rather "strange" to say the least.

FINALLY.  When the project is finished and I have a chance to get a friend to 
take pictures I'll put this project up in the homebrew section of my website, 
along with the other "projects" already there.

73 de Phil,  KO6BB
SWL QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
THE BEACONEER'S LAIR:    http://www.geocities.com/ko6bb/
Merced, Central California, 37.3N  120.48W  CM97sh