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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Fri 20, 2016 2:24 pm 
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Location: aston, pa, usa
I'm thinking of adding the 1,228 osc and correct choke as a two part kit for any one stuck with the 1,000 in a bad frequency city. PM me if interested.
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There has been member interest so I'll gather a member list for about two weeks then special order the parts.

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Sun 22, 2016 12:25 pm 
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Joined: Apr Fri 24, 2009 2:14 am
Posts: 491
Location: Charleston SC .. USA
Finally got around to building this ... transmits very well .. but.. if I use a 9v battery it drains the battery quickly and if I use the power supply as in the schematic .. the LM386 gets very hot and the Crystal also gets pretty hot .. and the LED does not change with the adjustment of the cap..the 386 and crystal still gets warm with the 9v battery,, I am using a 300ma 12.v transformer from radio shack.. I tried using a LM317 set to 8.5v by passing the led.. but they still get hot


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Sun 22, 2016 8:53 pm 
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Location: Texas
Mike3 wrote:
Finally got around to building this ... transmits very well .. but.. if I use a 9v battery it drains the battery quickly and if I use the power supply as in the schematic .. the LM386 gets very hot and the Crystal also gets pretty hot .. and the LED does not change with the adjustment of the cap..the 386 and crystal still gets warm with the 9v battery,, I am using a 300ma 12.v transformer from radio shack.. I tried using a LM317 set to 8.5v by passing the led.. but they still get hot

Maybe you have a very absorptive environment that draws and absorbs more RF than the circuit is capable of outputting... :wink: Just kidding.

Seriously, first check your wiring to make sure there are no shorts or other power draining anomalies such as misread components. Sometimes just stepping back for a couple days provides enough distance for effective proofreading.

Also, something could be causing the 386 to oscillate, which the 386 is not prone to do. Oscillation is chiefly caused by feedback from the output getting into the input. Sometimes feedback is through power leads. Try putting a .01 capacitor directly from the 386 power lead to ground if you don't already have one there. Then try a 1 uF and a .001 uF. If that doesn't fix it, post a picture so we can try to help isolate the culprit.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Sun 22, 2016 9:21 pm 
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Macrohenry wrote:

Also, something could be causing the 386 to oscillate, which the 386 is not prone to do. Oscillation is chiefly caused by feedback from the output getting into the input. Sometimes feedback is through power leads. Try putting a .01 capacitor directly from the 386 power lead to ground if you don't already have one there. Then try a 1 uF and a .001 uF. If that doesn't fix it, post a picture so we can try to help isolate the culprit.


This ^^^ if you don't have a 470-680pf cap on audio input, the 386 is likely to draw excess current...

See revised schematic on first page...


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Tue 24, 2016 2:26 pm 
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Location: Charleston SC .. USA
Thanks for your replies.. I took a couple days away and then got back to the Transmitter.. For the life of me I cant find any mistakes .. I have the 470pf in place.. But the LM386 gets so hot if left on very long it will almost burn you.. And I burnt up one 1 mhs crystal .. by it getting too hot.. This is such a simple circuit .. frankly I am stumped... I have new parts coming thru.. so then I will breadboard .. to test .. then rebuild on another board.. Question .. all I could find were 1/4 watt inductors .. is that sufficient... I will say when it is on it will transmit very well even without an antenna.. just a couple alligator leads in series...


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Tue 24, 2016 3:47 pm 
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If you lost a osc as well there must be a issue in the tuning or LC circuitry...

Have you measured current draw?? Properly tuned the whole shebangs should not draw more than 11ma at 9v... Sub a current meter in place of the LED...


Tom


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Tue 24, 2016 4:10 pm 
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Location: Charleston SC .. USA
I got the Meter set at 200m and it reads 146.3 or there abouts using 6 aa's


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Tue 24, 2016 4:21 pm 
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Location: Charleston SC .. USA
Tuning the cap really doesn't change the reading much either


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Tue 24, 2016 5:28 pm 
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Location: Charleston SC .. USA
OK I just got some new 1mhz oscillators from jameco .. https://www.jameco.com/webapp/wcs/store ... 1_27861_-1 .. I assume these are what I need.. putting one of these into my transmitter .. then checking current draw its around 9-12 ma.. but can barely hear it with the radio right next to it.. also the crystal as supplied by Bill has continuity from the Voltage in and ground .. yet it does work and even tho it causes both it and the 386 to heat up it will transmit very well with great distance.. but the ones I got from jameco I can hardly hear..


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Wed 25, 2016 5:01 pm 
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I checked my osc that has lost all it's paint, with reverse polarity there is approx 500-700 ohms from B+ input to ground and RF out so there must be some protect diodes in place... I do have a group of older analog osc that can't be modulated without distortion, they do work fine driving a tube Tx...

I've blown a osc with a short on RF output, I reccomend checking your tuning cap to be sure it isn't shorted... Can just remove it as a test...


Tom


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Wed 25, 2016 6:01 pm 
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Location: Warner Robins, GA
I still need to build one of these.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Wed 25, 2016 6:07 pm 
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Location: Beautiful Downtown Burbank CA
The 4 oscillators I got from Jameco weren't very good. I had a perfectly tuned LM386 transmitter with 9.6V. Swapped a Jameco 1mhz oscillator and nothing, dead. Tried another and WOW. This thing almost pegged the field strength meter. I marked it and tried another, dead. Last one was dead, or so I thought. I had a very very slight sound coming out of the test radio.

I put the old oscillator back in, read the meter then swapped that really good oscillator back in to compare. Near double the meter reading! As I was peaking the (AA5) variable capacitor it died.
Emailed Jameco, they sent replacements that were dead. I figure they got a batch of 3V oscillators by mistake.

Only time I had an LM386 get hot was when I ran it without the speaker series e-cap.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Thu 26, 2016 1:29 pm 
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Posts: 2188
Location: aston, pa, usa
Mike3,

I should be ordering a new batch of osc from mouser soon. I'll send you one then. I still have your address from shipping your 6888 tube.

Bill

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: May Thu 26, 2016 9:31 pm 
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Joined: Apr Fri 24, 2009 2:14 am
Posts: 491
Location: Charleston SC .. USA
Thanks Bill


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jun Fri 10, 2016 4:39 pm 
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Joined: Apr Fri 24, 2009 2:14 am
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Location: Charleston SC .. USA
ok finally bought some 1mhz oscillators form a place in china .. 20 for 12 bucks shipped.. these are just great .. popped one in .. have great reception all over the house .. no heat issues .. the led even works they way its supposed to.. Great Transmitter.. better than a Vec 1290 I have... Thanks for all the help


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jun Fri 10, 2016 5:14 pm 
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Glad to hear it's sorted out...

Those VEK-1290 aren't a terrible xmitter, for price are OK(and use a LM386), before I started rolling my own I used one...


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jun Fri 10, 2016 9:35 pm 
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Mike3 wrote:
ok finally bought some 1mhz oscillators form a place in china .. 20 for 12 bucks shipped..

Want to sell one? Or provide a link to the seller?

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jun Sat 11, 2016 12:04 am 
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Mike3 wrote:
ok finally bought some 1mhz oscillators form a place in china .. 20 for 12 bucks shipped..


Have you tested all of them and were ANY better than the others? Any brand name?


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jun Sat 11, 2016 4:51 pm 
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Joined: Apr Fri 24, 2009 2:14 am
Posts: 491
Location: Charleston SC .. USA
fifties I will send you one free after I get around testing the rest .. Just PM me your address.. Mike haven't tested all them yet but will report back when I can get to it ...this is what is written on them... HO-12b 1.0000MHz HOSONIC 930 .... link you have to ask for the 5V version http://www.aliexpress.com/item/20pcs-Or ... 50039.html


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jul Tue 26, 2016 7:45 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 473
Location: Louisiana
I'm trying to get the parts together to build one of these.

Is C2 (the 470-500pf) supposed to be an adjustable trimmer cap?

Does L1 and L2 have iron cores? Or does that matter? (I'm looking at Mouser for these).

And I can't find a suitable C6 (0-50pf). Can someone post a link or part source of one that works?

Thank you
Alan


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