Can anyone tell me how this works?
Sorry, I'm still a noob.

http://www.youtube.com/watch?v=6bdqa9tu ... re=related

I'm glad you posted this. I've seen it before and wondered about it but didn't want to be the guinea pig and ask about it. I wondered if it was even real since there is so much spoofed stuff on youtube and instructables now. I'm looking forward to reading the explanations from those who know.

He's screen modulating the 12BE6 by connecting the plate of the 50C5 directly to pin #6... Will it work? Yeah no doubt but I suspect the quality is maybe 25% of the units we've built here in Homebrew...

Using a 12CS6 in place of the 12BE6 and inputting a audio signal from the 12AV6 into G3 would be far better... Would no doubt need a bias tweak for the 12CS6 but results will be far improved...

At any rate if you don't have/use a isolation transformer as suggested, that design will no doubt light up your world...


Tom

Because it would mimic carrier current?

No Mike he's using a antenna so it isn't carrier current, which refers to coupling the antenna to the AC line...

Curt was always critical of screen modulation for not giving amplification like applying signal to the control grid(s), but I've never felt it was a problem with a flea powered transmitter... With proper design, screen modulation will give excellent audio...

The issue I take with that design is coupling the antenna to the osc coil, which is going to cause frequency instability similar to the 6BM8 Tx design... Another negative is the wimpy 50C5 audio output transformer is going to give poor low frequency response, which will limit bass... Also not especially thrilled with the transformer input he's using, I prefer resistance coupled inputs and amplifiers so the transformer's possible limitations are never a factor...


Tom

I did this mod and the result was fair with a hum in the signal but not in the speaker. I guess I need to build a real transmitter from the ground up.

Hi all,

That's my video, just haven't been looking on this forum for a while. The previous commenters have it right, this is far from an optimal transmitter design, mostly just a way of proving it could be done in a minimalist way. It was inspired by thinking about a "Carl and Jerry" type scenario where you were trapped somewhere with an AA5 being the only piece of electronics available - could you turn it into a transmitter to call for help?

73, Bob W9RAN