One Tube 10M AM Transmitter Part 4

[@tvengineer1]

Years ago I used an carbon mic for a project, if you tap the mic several times against something hard it would improve its fidelity. Apparently the carbon granules sometimes stick together and tapping the mic loosen them up.

[@Steve-GM0HUU]

😂 Banging the handset off the table was something I remember folk doing years ago wih telephones that had carbon microphones.

[@JCWise-sf9ww]

That Intercom Transformer you used in the transmitter carbon mic modulation circuit there, reminded me of the magnetic amplifier transformer used in in the GE 105 console 1936 radio I restored not too long ago. The magnetic amplifier transformer has a primary resistance of about 2k or so. The two secondary coils in series, controlled colored red/green lights for the tuning indication, primary had varying DC plate current (from a 6C5) going through it, controlled buy the AGC voltage on the grid of the triode tube driving the magnetic amp transformer. We had to replace the open primary coil, luckily people have had a transformer mfg make a replacement coil assembly.

[@cwebs1000]

Thanks Mike. Love the old ways of doing radio. Hurry on getting the "After burner" on line. Carl AB1ZI

[@thomasvandevelde8157]

I just used 3V to 230V cheap power transformers as mike-to-grid back in my poorer days. Didn't have any problems whatsoever with this in 2 CB-transceivers I build, one around a ECC91 (that's a 6J6 for you guys across the pond) and another around a pair of CK5676s for some kid. In both cases I used a telephone-element and Heising modulation of a Xtal-oscillator running at some frequency in the CB-band. I know a lot of folks are gonna jump up at this suggestion, but hey it's better than nothing! And voice doesn't require anything over 3000 Hertz passing through anyways. The only major problem one might have is core saturation on the microphone side. Anyway, I loved this project and learned a lot so far! It might inspire me for a project in the near future since I have some battery tubes intended for Suppressor-modulation, like the Soviet 2P29P. Never thought this would actually work so well! Regards, Thomas

[@kennethandrysiak4130]

Glad you are going the extra measure to preserve that pristine audio from the carbon source. I note you are a proud owner of an H/P 334A distortion analyzer... lucky you! That gizmo has an AM detector in it so when you’re finished with coupling up your exciter to the linear you run audio distortion checks on the ‘system’. Ha ha. All in good fun. Love your channel. Can’t wait to witness your 1st contact with the rig.

[@acestudioscouk-Ace-G0ACE]

Good to see this taking shape. I hadn't thought in terms of DC resistance for the transformer. I'm learning all the time on this channel.

[@MIKROWAVE1]

Of course it could be a low resistance if the transformer were gigantic! But with small transformers with fine wire, they will have significant resistance. So more of an effect than by design.

[@acestudioscouk-Ace-G0ACE]

@@MIKROWAVE1 Thanks for the clarification Mike, I sometimes confuse myself when it comes to things AC & DC. To my shame, I did a year of evening classes, took and passed with credits my full UK ham licence without realising that you can have AC and DC on the same piece of wire! PS, please don't tell anyone about this shameful secret! 🤫

[@Steve-GM0HUU]

👍Thanks Mike.

[@TheGmr140]

Nice talk and project

[@whippoorwill1124]

Another great video Mike - thanks! Love the tongue-in-cheek comments at the end. Very impressive improvement in audio quality when you installed the final mic transformer. That's a pretty-looking meter on your linear; I'm looking forward to finding out what brand it is.

[@clytle374]

Interesting project. Hope to hear that extreme high fidelity carbon mic on the air soon. ;)

[@W4TRI_Ronny]

Nice project! Would a telephone carbon mic drive it without the transformer? Never used one before but I have two here.

[@MIKROWAVE1]

Should work with an ordinary output transformer like 8 or 10K to 8 ohms and maybe 12V bias.

[@n8nkqrp595]

You can run your boots and still call yourself QRP, Mike! I heard this on 80m coupla nights ago. Op was outputting 10w PEP and checked into the nets when they called for mobile/QRP checkins. Of course his 10w PEP was driving LDMOS devices in his boots. I couldn't believe it. And they took his checkin! The net recognized this madness! dit dit

[@jimgiordano8218]

I can't wait to see the "Foot Warmer"

[@manosdimis1194]

Good work... Please tell me would a 6L6 work better to upgrade the power output 10Watts.

[@XPFTP]

awsome i have yet to find a good amp build video. would love to do a 75m amp. a floater at 500.

[@winstonsmith478]

An interesting retro-modern mix would be a tube tx modulated with modern digital modes.

[@MirlitronOne]

Can't wait! 😳

[@SilntObsvr]

My mobile rig's manual claims it can run 10 m AM, up to 50 W (though with the little quad-band antenna on it, your 3-4 W from a more efficient antenna might have more reach). If I know when to listen, and it's not in the middle of work, and I can figure out the manual to get it set for AM... It's no tube rig, certainly doesn't have a carbon microphone, but it'd be my first contact that isn't through a local repeater (we've got 6 m, 2 m, and 70 cm here).

[@jimballantine4408]

Bit ot Mike but I've been reading up on the wonders of mag amps. Could you do a radio project maybe a relax with a MA instead of a tune?

[@G7VFY]

What about 6BW6 = CV2136 - British made miniature-tube 12W equivalent of the 6V6, 9-pin base B9A.

[@MIKROWAVE1]

The suppressor grid is usually tied internally in many pentodes. And beam power tubes will not modulate properly. So I don't think that valve is a candidate.

[@TheLightningStalker]

@@MIKROWAVE1 Can confirm triodes also do not work.

[@MIKROWAVE1]

@@TheLightningStalker But I triode anyway.

[@DAVIDGREGORYKERR]

what about a DSBSC modulator .

[@WaveformWanderlust]

Great series and channel. - K6ZW

[@jimballantine4408]

And that's a reflex not relax!

[@jimballantine4408]

Duh tube!

[@Capecodham]

"We got it working?" I only see you, when you raised the tube, the power was higher at least an inch higher. Replace the 6CL6 with a 4CX5000 then you will get out.