I have started a new project. Being kind of disappointed in the (so far) turn out of the mike osc, I did some research and came across a plan to build one from scratch. Sure, I could just buy a "Talking house" or some kind of kit, but what fun would that be? I kind of like the idea of something built from parts and otherwise junk pieces laying around. I am wanting to keep costs down, but don't want to skimp and end up with something that looks like a 5th grade science project! Anyway, to give credit where credit is due, I will be using a very simple circuit by Norm Leal, Tom (35Z5) and ideas from Mike Toon (ARF).
I chose a 50's Blonder Tongue UHF tuner (useless, right??) for the project box, and sacrificed a 'barn find' PC board AA5 for some parts. The transmitter will be on 1000 KHZ, which is fairly clean in my area. I can retune it if needed with a different crystal and coils.
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Here is the schematic I am planning on using. There are several variations, but to try to keep things simple, I am planning going with a one toober. This uses a 6888 tube. It is a 'computer' tube of all things, and is dual control.
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hey tim
you can build this type seams to work very well
sam
I'd reccomend leaving a "empty" area so if you decide to add a audio amp and/or VFO you won't be scrambling to find space...
Very nice Sam!
Did you build that? Thanks for the ideas. I am going to keep these schematics in a file. I am sure this will not be my last transmitter build. For some reason I am facinated by all this. Thanks Fenbach for the links. I had thought pretty hard about a 2 tube similar to the one Sam posted, but probably am going to start with the simple one tuber and go from there. I do plan to keep the 7 pin tube socket in case I want to add a preamp tube. It'll be right there. I am hoping to set this up so I can fire it up and let it run 24-7 if I want.
TV MAN- What device are you going to use to run a signal run through that?
It will be a line level, such as a CD, MP3 player or a FM tuner. I had kind of had the idea to use a walkman style CD/FM to set it to our local station so I can tune it in anytime I want on any radio. Dollar General had one for around $15 that I have used pretty often. Since it has a volume control, I can set the output to work on about anything.
* Just a note, if you look at this circuit, it is using an output transformer from an AA5 turned in reverse. So, you feed the signal into the speaker side, and that raises it to feed the 6888 tube*
I have been told this works well. If not, I will add a 6AV6 or something to amplify.
The reason I add preamp & gain control is for line level signal, input transformer is for direct coupling from a amp output... I orignally built my 6888 without the preamp, next day I was adding it...
The low impedance of std output xfomer will likely load a line signal till it'll be unusable...
I still use the one that 35Z5 helped us build and have pictures somewhere.
Beyond modulation hum, the usual issue for driving anything tube-type is getting enough voltage out of solid state devices, current doesn't count unless you are going to drive an interstage transformer (you don't want a voltage drop by the load).
I use an old laptop which gives me a better level than my other small devices.
That does make sense, using speaker level source to drive the transformer. Sounds like I need to adapt to a 2 tuber to get the level I need. Not a problem. This just helped me to make the decision, and would be a lot easier to do while I am building to begin with. Honestly, in my past creations I have used more amplification that was really needed, even had to take out a preamp stage once because I had too much. So, this time I was going to use the minimum. Ok, so to preamp it is!
hi tim
I have to admit way beyond me
bought for 20.00 figured could not go wrong
sending pm on it
sam
I have been studying the circuit Sam posted and I can see several things l like about it. One in particular, and that is the tuning cap is not connected to B+. That had bothered me, since that is a pretty large part to have that kind voltage on it. Then, there was the isolation issue. With this circuit, the tuning cap can be mounted directly to the chassis to ground. Really simplifies things. I am mocking up a potential layout. I will post some pics of the idea and see what you all think. I want to avoid feedback, hum and noise.
Thanks for the pics Russ! It looks like you are using a 6AV6 and possibly a 6BE6 (or 12v versions?). Do you have any hum problems? Also, what is your frequency? I see a small (RF) coil coming off the VC, and a (gimmick) coil near it? What coil are you using? This is an area that I have had a lot of difficulty finding accurate, consistent information.