Finally a transmitter utilizing a single, cheap surplus transformer... Norm found xfomers at EGM with 24V & 36v windings that work great and I've been designing around it and the cheap(did I mention cheap?) 12CS6, many vendors have these for a $1 each... Also uses the common 12AV6 or 12AT6 almost everyone should have one of these laying around...

Broken links have been repaired 7/24/15



R/S PCB is cut in half and holes drilled to route wires from underside to one side, where the bundle(five wires) is tied together... This allows top cover to be raised at 90* angle without stressing wiring... Chassis wiring, utilizes one of Bob Weaver's Earth Potential Facilitators, for grounding...


http://s6.postimg.org/kaqnjy6bl/12cs6txb.jpg

http://s6.postimg.org/k9gpqj4ht/12cs6txa.jpg

http://s6.postimg.org/rmribqz5t/12cs6txc.jpg

http://s6.postimg.org/b0ejgevlt/12cs6txd.jpg


Tom

Tom

Looks great, noticed that release date 4-01-10.

Bill - I have plenty of these transformers and EGM has thousands. Shouldn't have a problem with running out. I can send you groups of 12, Priority Mail, when needed. They can also be bought direct from EGM.

Sneak preview...

BTW Radio Shack parts are either up grade(VR-1) or components not included in Bill's kit...

Tom

anyway to make the schematic in a downloadable word or pdf file?hard to print or copy from forum page.
thanks
Harold

Right click on the image. When the dialogue box opens, click on "view image". The image will open by itself in a new page. Either print or save that image.

And the hits just keep coming!

Fantastic how we *cough* I mean YOU keep churning out great alternatives. Eh, I'm just a fabricator here; I gaze in wonderment at the designs.

I've built a really nice desktop headphone amp with these 12-volt car radio tubes and they do work very well and are readily available (and for the most part, cheap).

I built this one:
http://www.diyforums.org/MAX/MAXoverview.php

It's off my desk now for a tune-up after about 2-years of nearly daily use. It doesn't use high plate voltages so it uses a 24-volt AC Wall-wart.

Keep 'em coming. Maybe we need to put the 'reference' designs in a spot in the 'resources' area of ARF. There's the 6888, the 2-tube 6888, the 6LE8, the two-tube 6GY6... now 12-V tubes.

Mike Y
Dallas, Texas

What's the difference between the 12CS6 and 12BE6? I see them listed as one being a sub for the other.

Hi

Transconductance from grid #3 is specified on a 12CS6. A 12BE6 is an older tube which doesn't have transconductance from grid #3 controlled as well.

We use grid #3 as audio input so nice to know what to expect. Tom has done experimenting with different tubes. 12BE6 works but doesn't modulate as well. He will probably give details.

The 12BE6 has a remote cutoff G3 and will distort with higher levels of audio input, same is basically true of virtually all pentagrid tubes used as mixer-osc in BCB radios... Most charts list 12BE6 & 12CS6 as subs, in reality neither likely perform for the other as intended...

Tom

That's about what I was thinking, since 12CS6 is listed as a Dual Control Heptode. I was surprised to see them listed as subs for each other.

Tom, How does this transmitter compare to the 6LE8 & 6GY6 transmitters for output power, sound quality etc.?

Well there's an idea, make a BCB tx using 12V space charge tubes

LOL... Done in 24v & 30v versions...

http://www.antiqueradios.com/forums/vie ... p?t=128480

BTW most of the low voltage tubes used in the car radios were not actually space charge types, I believe only the ones used as audio drivers were space charge, other are conventional tubes optimized to operate at low voltages...

Norm's EGM transformer could be used for this low voltage Tx, could even build a "50v" version using the 36v winding for B+...

Tom

Sounds like a 3BY6/6BY6 would work also then if using a different filament arrangement.

Carl

Sound quality is fine, only issue is it's easy to over-modulate with the 12AV6, a audio taper gain control is defiantly recommended... The RF output is approx 65% of the 6GY6, which has the advantage of not over loading the front end of a nearby radio... A 6GY6 version could be built using the CT of the 36v winding to buck the 24v winding, that would require use of a tripler P/S to get the B+ back up to near 150v...



Yes the *BY6 works(as does the 5915) but has considerably less Gm on G3, thus requires a higher level of audio input(not necessarily a bad point)...

I'm surprised no ones has commented on the power supply, specifically to the xtal osc...

Tom

I'm surprised no ones has commented on the power supply, specifically to the xtal osc...

Tom
----------------------------------------------------
What kinky things have you done to the xtal?

Is someone going to be selling all these parts as kits ?

Carlos

Hmm, hadn't noticed that. Very clever.

Posted updated schematic dated 04-10-10, if you D/L the earlier version(04-01-10), please destroy it...

R7 & R8 have changed value and L3 was added to convert sq wave to a sign, gives improved modulation and a bit more RF output...

Likely this will be the only change ever made to this Tx, I've ran the prototype several hours and am very satisfied with it's performance...

Tom

I have already built the pcb section of the circuit with the parts that Bill Hamre sent me. I am looking forward to getting the rest of the parts so I can finish building and try this transmitter.

Can you tell me what type of antenna I should use ?

Thanks,
Carlos