Thursday, September 20, 2012

Project Clean Up Part 1 Chapter 3

Chapter 3: "Totally Tubluar Transmission and Technical Tidbits"


This is a continuation, the First part is Here,  a complete list is available under "Ham Radio Master links" on the sidebar.

Now that I am reasonably sure of my polarity, and I'm done cussin' the feller who put this plug together, it's time to go over the transmitter itself, and see if there's any improvement to be made. Heh. My radio uses 2 6AQ5A's in parallel. The filament takes 6 volts, and are wired in series. Right off the bat I saw that I had I had the filaments wired in parallel. This was from a time when the only transformer I could find was a 120v AC to 6v AC. I certainly corrected that lil' problem. It also explained why the sucker glowed a lil' more than I expected the first time I lit it up. 12v on a 6v filament will do that. I'm glad I didn't blow the tubes! I also cleaned up some wire and leads underneath, and made sure my point to point all went to the right places. In the process, I discovered a cold solder joint, and found a better way to route some parts.
The Kind of Ugly that's a Pretty all of it's Own





It's not necessarily my best work, but hey, it will do!
And yep, that's three 33pf NP0 capacitors wired in parallel.





 

Time to do some testing.
first, go see Dave Benson's website, Small Wonder Labs, and order a rockmite :) also, check out his documentation section. Download a manual for the SW-40+ transceiver, and look in the testing section. In that section is a circuit you can make pretty easily, and use it to measure the power your radio is putting out. I built mine on some radio
Circuit, dummy load, and babyfood jar.
 Prototyping board, specifically so that things would stay together. I connected the orange and yellow wire across the dummy load, and made sure that I hooked the yellow wire to the side that goes to the pin, and the orange wire to the side that goes to the ground side of the plug. At the measuring end of the plug are two posts made from surplus resistor leads, I hook my Digital VOM to them using probe hooks. The set up is hands free once you hook the probes onto the posts, and turn on the VOM.



Here's a little video about what I discovered when I measured the voltage across the dummy load:
 Ok, so, according to theory, the voltage measured here is Peak-to-Peak voltage.
Knowing that, tell me how much power is getting to the dummy load.
Show your work!

Continue on To Chapter 4: "Clean Up and Key Down"

2 comments:

Steve Smith WB6TNL said...

Yes I can tell you. The question is, can you tell us? I have a number, we'll see if it matches what you derive. :-)

FWIW, the accuracy of your measurement depends a lot upon your load and to a degree the accuracy of your DVM.

I like that chirp. Gives the little rig character and it will stand on on the band.

73.......Steve Smith WB6TNL
"Snort Rosin"

G. Brandon Hoyt said...

Heh,
I'll tell you mine if you send an email:) I can't find a way to send you an email from your blog.
I've actually seen about 4 different ways of calculating the power, fortunately all of them seem to come up with same answer. Biggest gotcha for me with this has been figuring out if I've been measure Peak voltage, or Peak to peak, I confirmed with the one who would know that this circuit is measuring Vp-p. I hope to cover the math next post. Tonight I will be prettying up the power supply, taping down some caps, shortening some wires, making everything tidy to reduce the risk of shorting something out. Then, I will be QRV on 3579ish. I will announce on twitter and the SKCC facebook group when I get QRV.