Another radio!

Time for an update!

I've spent a lot of time recently, collecting parts for my current projects, the battery eliminator and AM transmitter. I just finished the transmitter, and last night I fired it up for the first time. Amazing! It actually worked! Huge thanks to Bob, VE1ARN, who generously sent me a tube and socket for free.

This is a really simple design, that was put together by Syl.

I modified it based on some suggestions from Mike T. The following is an "as-built" schematic. This reflects a different power supply. The Granco UHF tuner that supplied the chassis had the transformer I need. It also has a really nice bakelite case that polished up beautifully with a rag and some Brasso. This modified schematic uses a voltage doubler, to take the voltage up from the standard 180-something, to about 385, which then gets dropped back down to about 275, which is just short of the max allowed by the 6BM8 tube. Hopefully I will get better range than I would with the standard 180.

This is an interesting design. It's really simple, but not "frequency stable" by a long-shot. Everything you do changes the frequency. You can modify the coils or caps, but even putting your hand near it will pull it off-frequency. I had some fun with this effect last night. I put my radio on SSB, and tuned it to the transmitter's frequency. This produced a tone, from the beating between the transmitter's carrier and the BFO of the radio. I was using a 3' whip antenna on the transmitter. If I brought my hand near the antenna, it caused the pitch of the het to change. Waving your hand around, you could get some pretty cool effects. A lot like a Theremin.

Anyhow, the frequency of this transmitter varies based on the antenna you use. So with the whip, I was around 1200 Khz. With a hunk of wire, it was closer to 1130, but when I hooked it to a spare pair in my phone jack, it went way down to 994 Khz. One thing I forgot to do - the original schematic has a fixed 20pf mica cap at C10. I need to change that to a variable, so that I can have some frequency adjustability (apart from what I get just being near the transmitter). Once I get my antenna built, I will take a few turns of wire off the primary of the oscillator coil, so that I can tune it to a more open frequency. My son is already looking forward to being a DJ!

I finally have all of the parts I needed for the battery eliminator. My parts order got lost in the mail, and it took 6 weeks to get it replaced. But everything is here now, and when i get a chance, I will put that together. I'm going to put it inside a box with this design. I know it's not truly authentic, since my battery eliminator will be an A/B supply, not just a "B" like this one, but I think I should be able to modify it to add connectors for the "A" supply. And it will look really cool.

So now, you've read all this stuff, and you're wondering: What about the new radio mentioned in the title? Well, the wait is over. Check this out:


This is a Philco 89 console. Aside from a ding in one of the upper columns, and the veneer on the lower middle front, it looks to be in really good shape. These are the eBay pictures. I hope to have some more once I've picked up the radio. At the moment my son has my camera with him on a backpacking trip, so it will be a little while before I can get any pictures to put up here. I promise I'll post some pictures of the transmitter too - I'm pretty proud of how it came out, both in performance and looks.

Lastly, I guess I should update the status of the Philco 70. Not much to report there, except that a couple of weeks ago I found out that someone was giving away a Ryobi scrollsaw and bandsaw. Free! Perfect for my non-existent budget! Unfortunately I was just a bit too late, and someone else got it before I did. Bummer.

I'd love to get a scrollsaw - both for the Philco 70 project, and to play around with other neat things. The problem is that I have such limited time, that I really can't justify spending the money on it right now, since it probably won't get much use. So instead, I went to Home Depot and bought a coping saw, some extra blades, and a piece of 1/4" plywood. I'm going to try to make the front panel with these. The plywood was only $3, so if I mess up, I can just start again. If I can get a reasonable facsimile of the front panel made, then I'll invest in some veneer.

It's summer now, which means no homework to help with, and more flexible bedtimes for everyone. So I hope to be able to spend a bit more time on my radios. I've already succeeded with the transmitter, so I'm hopeful that I will be able to do the same with the other projects. I certainly have learned a lot by building the transmitter.

Now look at this fine mess I've gotten myself into...

Well, things seem to only go from bad to worse with the Philco 70. Here's what the front panel looks like now:



The last time I posted, I showed how the previously nice & flat panel had warped badly. I wet it down and clamped it. That helped, but not enough. So I did it again. This time it not only stayed warped, but as it dried, the various layers dried at different rates. This caused the front part of the panel to crack and split. I think it's pretty well shot now.

So I figure I have two choices. Buy a whole new repro cabinet (or junker cabinet that's in better shape than mine), or figure out how to make one myself. Buying one is expensive, and I'm still not ready to give up.

Even so, I'm not sure how I'm going to do this. It doesn't look like it would be that hard - just trace the pattern onto a new piece of wood, cut it out with a scrollsaw or something similar, and put some veneer over it. Of course things always seem easy until you've actually tried to do it.

I guess we'll just have to see what I can do.

In the meantime, I've got two other smaller projects I'm trying to work on. First is a battery eliminator for my Silvertone farm radio. I've got almost all of the parts together for that - I'm just waiting on one more order to arrive. The other is an AM transmitter. As much as I like AM radio, there really isn't much there I want to listen to. So if I build my own transmitter then I can listen to the stuff I like to listen to. And best of all, there won't be any commercials :-)

I've got most of the parts for this one, but I am waiting on a few more items. I'm planning to use a slightly modified version of Syl's 6BM8 design. The mods came from tubbytwo, who used a voltage doubler in the power supply circuit. The idea being that since the tube can handle a lot more than the 160v in the original design, we can get better performance with little additional work or cost. We shall see how that goes.

Anyhow, the shell of this project began life as a Granco UHF tuner. I will be gutting it soon, and will hopefully get this project going as soon as more of the parts arrive. Originally, I bought an Astatic TV signal booster for this purpose, but once it arrived, I realized that the transformer did not have the high voltage secondary winding that I needed for this project. I suppose I could have made it work using the high-voltage circuit that it already had, but similar to an All-American-Five design, it has a hot chassis. I really don't want anything with a hot chassis around my house. Not with a very curious 2-year-old wandering around. For a few bucks more I got the Granco, and now I'm good to go.

So that's where I'm at. I have had almost no time recently to work on this stuff - just a few minutes here and there. Hopefully this will change soon (haven't I said this before?).