LM386N MK-XI BCB Transmitter

35Z5 · **Joined:** Jan Thu 01, 1970 1:00 am **Posts:** 11777

I've spent more time in development with this little guy than most of the tube units... Sound quality is very good and the current drain at 9v is only 11ma, so can be easily powered by a std 9v battery... The coil coupling the audio to the osc is very important, without it current draw is increased by 60%, is essential for good life if using battery...

Unit is built in a discarded satellite tuner... The meter is in series with B+ so takes place of tuning LED on schematic...

On-off sw & gain(level) are operational... Single lighted LED indicates standby or both for power on...

My unit is built semi-modular, board can easily be removed for service or modification... Plug with brown, orange and red wires connects to the power indicator LEDs(has standby and in operation modes)... Audio is fed from gain pot on front panel through the large connector and one at it's upper right connects to ammeter on front panel(in series with B+), lower plug connects ant tuning cap... LM7809 regulator installed at angle for cover clearance...

Large black item is a cover over the line fuse also has a scrap piece of pref board Velcroed over 120v connections to power transformer...

Better shot of board & tuning cap, antenna peaking performed from back panel...

Belly shot of the PCB and 110ma @ 10v xfomer...

Tube Radio · **Posted:** May Mon 07, 2012 3:43 am

Very nice work.

ke4nu · **Posted:** May Tue 08, 2012 7:12 pm

Looks good and simple. I'll have to give it a try soon as I get a crystal osc...thanks for your hard work..alan

bill hamre · **Posted:** May Thu 10, 2012 3:30 am

This is great. I'll start to get kits together.

Sam T · **Posted:** May Thu 10, 2012 8:12 pm

A kit? That'd be great, Bill.
Can I ask, offer a choice between the 1 mhz osc and the 1.228 please?

And I want to be first in line, I'll take two kits.

-Sam T.

35Z5 · **Joined:** Jan Thu 01, 1970 1:00 am **Posts:** 11777

I've tried using a sq wave from my signal gen and as long as the trimmer cap will tune down to 10pf or so(padders usually won't adj completely to 0), the 330uh coil will match 1228Kc to a 10ft antenna... Unfortunately I don't have 1228 osc to try, with a 1230 local, I don't generally keep one on hand... Worse case is the coil will have to be changed to 270uh or maybe a 47- 68pf added in series with the trimmer...

Tom

ke4nu · **Posted:** May Fri 11, 2012 1:32 am

Bill, I'll take a kit too..thanks, Alan

bill hamre · **Posted:** May Fri 11, 2012 6:11 pm

Give us a couple of weeks and I'll get kits to everyone. In the meantime PM your mailing addresses.

TJM70 · **Posted:** May Mon 14, 2012 8:30 pm

Bill...I'll PM you too - I think I have the itch to build another of the famous 35z5 designs! Count me for one.

bill hamre · **Posted:** May Wed 30, 2012 7:58 pm

All kits are shipped.

ke4nu · **Posted:** May Wed 30, 2012 9:10 pm

fantastic!!! thanks, Alan

Rich, W3HWJ · **Posted:** May Wed 30, 2012 10:27 pm

Looks like a nifty idea, but a couple of questions:

1. The ECS oscillator is TTL and rated for 5V +/- 0.25V. Does the modulated voltage exceed that?

http://www.ecsxtal.com/store/pdf/ecs_100.pdf

2. The ECS runs as a modulated oscillator in this application. Does than cause some FM? Probably even if it does, it isn't a handicap?

Rich

35Z5 · **Joined:** Jan Thu 01, 1970 1:00 am **Posts:** 11777

Hi Rich

Audio signal required for full modulation is approx same PP as the DC input to osc... The LM386 outputs approx 50% of B+ so at 9v should be 4.5v, though I have seen variances between ICs close to .5v...

Norm has reasoned it should not be able to modulate 100% without killing the osc, but I can push it deep into over modulation and osc keeps running, of course distortion is a issue and seems to start being noticeable at approx 85% modulation... I have some older Dale osc that start "chopping" due to osc cutout at only 20-25% modulation, the ECS osc exhibits none of this trait... I haven't noticed any FMing issue(maybe in that last 15% modulation?)... Varying the B+ & using a counter, there wasn't a freq shift at any voltage between enough to keep osc running(less than 3v) to over 6v...

While I hate to admit it, basically this little Tx is so good it pisses me off... Spent hours building tube units(that I'll continue to use), can throw one of these together on a breadboard in just a couple minutes... If I could, only thing that I'd change would be a VFO or maybe a larger selection of IC freq...

Tom

rocketeer · **Posted:** May Thu 31, 2012 1:23 pm

Bill I'd like a kit if there are any left. PM sent.

Thanks,
Larry

bill hamre · **Posted:** May Thu 31, 2012 5:32 pm

To all members awaiting kits, don't buy anything as there are backorders happening on some items. I'll have everything there soon except VC-1 which may take another week. PM me with any specific questions. Bill

rocketeer · **Posted:** May Thu 31, 2012 8:54 pm

No rush, whenever it's ready.

Larry

35Z5 · **Joined:** Jan Thu 01, 1970 1:00 am **Posts:** 11777

For those who like waveforms, here are the modulation envelope using music and trapezoidal WF with approx 800cps tone... Both are at near 100% modulation...

Blustar1 · **Joined:** Jan Mon 04, 2010 2:52 am **Posts:** 4308

35Z5 said: "While I hate to admit it, basically this little Tx is so good it pisses me off... Spent hours building tube units(that I'll continue to use), can throw one of these together on a breadboard in just a couple minutes... If I could, only thing that I'd change would be a VFO or maybe a larger selection of IC freq..."

I doubt it Tom. I would choose your 12AV6-12CS6 transmitter any day.

bill hamre · **Posted:** Jun Fri 01, 2012 6:01 pm

35Z5 said: "While I hate to admit it, basically this little Tx is so good it pisses me off... Spent hours building tube units(that I'll continue to use), can throw one of these together on a breadboard in just a couple minutes... If I could, only thing that I'd change would be a VFO or maybe a larger selection of IC freq..."

I doubt it Tom. I would choose your 12AV6-12CS6 transmitter any day.

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Tom, Between you and Norm we all got the best of both worlds! Also, if compared to the knightkit 3 tube from days of old this needed to be done. The fact that we all now need AM content is the cherry on top.

35Z5 · **Joined:** Jan Thu 01, 1970 1:00 am **Posts:** 11777

Blustar1 wrote:

35Z5 said: "While I hate to admit it, basically this little Tx is so good it pisses me off... Spent hours building tube units(that I'll continue to use), can throw one of these together on a breadboard in just a couple minutes... If I could, only thing that I'd change would be a VFO or maybe a larger selection of IC freq..."

I doubt it Tom. I would choose your 12AV6-12CS6 transmitter any day.

I'm not discounting the audio quality of the tube units, they're very good, it's the capability of "almost nothing" that's astounding...

The idea for this Tx isn't mine, giving credit where it's due, Mike Toon posted a slightly simpler version last year but I could not get much more than a bunch of squealing from the one I built... Mostly the problem was the LM386L IC I purchased that absolutely would not tolerate RF feedback from the osc... After trying a alternate configuration that modulated the ground side of the osc, I realized it was a RF issue and went back to a similar circuit as orig but with the added coil for isolation... From that point, it was come up with a good antenna conversion/matching network, in the end proved far simpler than I'd imagined...

Tom

LM386N MK-XI BCB Transmitter

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