Now on to the business end of the of the project...The RF Deck!
The RF deck was a lot fun to put together. I ran into several
challenges in the
construction phase. First of all was trying to fit all of the components in the chassis. Then the
placement of these parts comes into play. Looking back now, if I did it again...and I will,
I now have a better understanding where to place components within the chassis.
Starting after the tube is the plate choke.
It is hand formed and wrapped
around a 1" piece of teflon rod. It is about 6" long and is made from #22 formvar transformer
wire. I used a grid dip meter to verify I had "no birdies" in the ham bands. I only had to modify
this choke once to achieve this, lucky me! Next is the plate parasitic. Its formed from 1/2" wide
copper strip and has a U shape to it and there are several resistors across it. Also, 2-30kv doorknob caps which finish up the parasitic.
Now onto the tank circut. The plate
capacitor is a 375pf/14kv vacuum variable. The
inductor is of the roller type having an inductance of about 11uh. The antenna capacitor is a 1000pf air variable. Nothing fancy...I wanted to find a vacuum variable for the antenna side but my luck didn't hold out. The ones I did find were pricey. There is no great need for a vacuum variable cap here, so the air cap will have to do. As it stands right now, this amp operates from 10-80 meters. I just do not have the room to add 160m at this point in time.
The RF deck HAS been upgraded
TX on 160 meters. Completed in October, 2000!
Photos of the new RF Deck
can be seen by clicking here...
On the rear of the RF deck there are several points of connection. The
B+ has its own
HV connector. There are two BNC jacks, one for RF in from the exciter, and the other is for the
bias control. There are two lugs that are insulated from the chassis just to the left of where the
4" drier hose is connected. These are the filaments and cathode connections. (I keep the blower
motor outside of the room because of noise. It is 6" in dia. and can really push some air!)
Also on the back is a small compartment that houses the TX relay.
The chassis for all three
sections of the amplifier are made out of old street signs. Yes I
said street signs. They are fastened together using 1/2" aluminum angle. The HV and intermediate
supplies (bias, screen, filaments, ect.) are fitted in a standard 19" rack cabinet. The RF deck utilizes an old Heathkit DX-100 cabinet. The tube compartment was an old aluminum box that I
modified. I drilled out, cut, and then filed the shape of the socket. On the side of the tube
compartment you can see where the bias and RF feeds are connected.
The total cost of this amp
was about $600.00. Yup, that's it... I did a lot of hamfesting,
internet searching, and recycling of old parts grabbed from old equipment. Thanks to John
K1JI and Denis W1WV for there help with this project. Without them, you would not be reading
this page right now!
Well, that's about it. Thanks for stopping by and showing interest in my project. And I hope you enjoyed your visit. I also welcome your comments or suggestions on this page. This was something I thought I never could do. But it goes to show you, if you put your mind to it, you can do anything. And by the way, there are plans in the making for a 6 meter RF deck using the same tube. Oh boy!
One more thing, Im am not an electronic guru. Im an auto technician
by trade. So
there is a lot of room for improvement here. The main thing is I had a blast building this
amplifier and I got a great education out it. I have seen many other homebrew HF amps
out there, and many are much better than mine. As I mess with these things more and more,
and talk with people who have build a few of these, I hope to further my understanding of
the mighty RF amplifier.....Thanks to everyone who has helped me!
E-mail me with your comments...
Check out these other amplifier related sites!
Homebrew Amplifier Showcase!
W1WV's 2 meter 4CX250 amplifier!
AC6V...Great info on homebrewing!
Eimac Varian...Tube manufacturer and info.
Svetlana...Tube manufacturer and info on use of the "4CX1600B"!