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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Fri 29, 2016 4:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20688
Location: Warner Robins, GA
If you have two radios with similar speakers and power outputs or you have two identical radios it should work.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Fri 29, 2016 5:49 pm 
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Location: Mesquite NV 89027 (from Coventry, UK)
Very nice, David.

Colin


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Sat 30, 2016 12:44 pm 
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Joined: Nov Wed 09, 2011 4:07 am
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Location: MD-DC 20855
Would you like to swap that one for a 1.2288MHz oscillator? All that
would cost each of us would be first class postage, probably 2.00-2.50 or so...

David



tack wrote:
I think I'll get one and see how it does. My order for parts from Mouser came in today, including the 1.00mhz osc. I wasn't thinking when I ordered it, as that is the same freq as a nearby radio station. Mouser has this: http://www.mouser.com/ProductDetail/ECS ... Uiw7axU%3d

But shipping will be more than the part.

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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: May Sat 28, 2016 6:09 pm 
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Joined: May Fri 25, 2012 3:31 am
Posts: 514
Location: Clayton, Ind.
I'm back to finding the last pieces for the kit - I think all I need is a BAV21 and the tube sockets and the 75-200 pf trimmer cap. Was thinking of finding the latter with a 125 pf range and then padding. But:

Noticed on Dan's Small Parts web site (link below) a dual ceramic trimmer, to-wit:

DUAL CERAMIC MICA TRIMMER CAP..350 VDC
50PF ONE SECTION..150PF OTHER SECTION

Side by side. Five for a buck and a half (plus shipping by priority mail....unless USPS and at least $50).

Seems that would work for the 75-200, right?

http://danscloseoutsandspecialdeals.com ... overs.html

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TDane WA9YI

Radio is a divine gift; God made us able to do one thing while listening to another.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: May Tue 31, 2016 6:07 pm 
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Location: Warner Robins, GA
That may work. Suppose it will give both a coarse and fine adjustment.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jun Sun 12, 2016 4:53 pm 
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Location: Clayton, Ind.
I meant 50 to 200 pf, and thus 150 pf range - bad, memory, bad!

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TDane WA9YI

Radio is a divine gift; God made us able to do one thing while listening to another.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Sat 20, 2016 2:32 am 
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Posts: 7
Hello, just finished building this transmitter. Powered up with no smoke, good start. Not having any success receiving its transmission though.

Three areas I guessed at -

The ferrite inductors, I could not find any info about polarity. The pcb had a dot, but the part had no marking for polarity. Is it important?

Antennae length. Guessed at 6'. Doubt that is a problem.

Mono jack. From what I researched, a stereo 3.5mm stereo plug should work in a mono jack, but will only pass left channel. Ok?

My first pcb build. Went very well I thought, just need to get it to work!

Thanks in advance for any advice.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Sat 20, 2016 5:39 am 
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Think it must be the inductors. Reviewing the digikey part schematic, there are two coils in each part and the pinout pattern is 4mm x 5mm. I thought it was square. ..

I tried to remove the inductors to check, ruined one.

It will be a few days before I get replacements, wish me luck...


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Sat 20, 2016 6:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2367
Location: Saskatoon
Polarity doesn't matter on those inductors.

The first thing I'd check is to make sure the boost converter part of the circuit is working, and check with a voltmeter that you are getting the required high voltage.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Sat 20, 2016 6:49 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 13348
Location: Omak,wa,usa
Hello clutter
Nice job looks great
Anyway Colin's yours looks very nice too


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Mon 22, 2016 4:48 pm 
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BobWeaver wrote:
Polarity doesn't matter on those inductors.

The first thing I'd check is to make sure the boost converter part of the circuit is working, and check with a voltmeter that you are getting the required high voltage.


Polarity was probably the wrong term for me to use. Looking at the inductor schematic and following the circuits on the PCB, the way the inductor is installed must matter and chances are good that I guessed wrong (90* off). Now that I understand the 4 and 5 mm leg spacing and the coil locations I'm confident i'll install my replacement inductors correctly.





Attachment:
Inductor.JPG
Inductor.JPG [ 59.86 KiB | Viewed 6267 times ]


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Mon 22, 2016 10:22 pm 
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Location: Warner Robins, GA
Oh I see so you probably had it to where pins 1 & 3 were connected in the circuit.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Wed 24, 2016 4:09 pm 
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BobWeaver wrote:
Polarity doesn't matter on those inductors.

The first thing I'd check is to make sure the boost converter part of the circuit is working, and check with a voltmeter that you are getting the required high voltage.


(Humble Pie) - You are completely correct. No matter how you "clock" the 4 pin inductors, the contacts will cross pins 2 and 4.

I should have my replacement inductors today and will reinstall and continue troubleshooting. Boost converter is working correctly and B+ voltages are high enough to bring the led to full brightness. Think it is something on the RF side.


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Thu 25, 2016 12:43 am 
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Posts: 7
Replacement inductors are installed.

The carrier frequency is transmitting, I can pick it up on my AM radio, but the audio is not modulating.

Any advice on what to look at?

Thanks,
Matt


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Mon 29, 2016 7:44 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3077
Location: aston, pa, usa
Just 36, 6888 tubes left in inventory. If you want one to build this version of the 6888 broadcaster just PM me with your mailing address.

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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Mon 29, 2016 8:08 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1129
Location: Dallas, Texas USA
Heck, I'd start from the connector and go forward.
If you have a little audio amplifier & speaker, or better a 'scopy, you can test this all the way to the grid of wherever the Audio goes in.

Not sure which schematic you're using. If you're using this one - viewtopic.php?t=63310
1. Check the audio at the input of the isolation transformer.
2. Check the output - you could be wrong-way 'round on the transformer
3. Check Pin 3 on the 6888... is there still audio?

If you hear a carrier (or it 'silences' the frequency when you power on), you're REAL close.

Oddball situations:
I have found with some setups - cheap Chinese radios - the 'headphone output' is mono, but the audio goes across the tip & ring - there is no ground.
This is fine for a plain-jane $2 stereo headphone - it PLAYS fine.
But if you feed this into your transmitter input - there is no GROUND - so there will be no audio.
I only mention 'cause it came up for me, recently.

Mike Yancey, KM5Z
Dallas, Texas

Solamar wrote:
Replacement inductors are installed.

The carrier frequency is transmitting, I can pick it up on my AM radio, but the audio is not modulating.

Any advice on what to look at?

Thanks,
Matt


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Aug Tue 30, 2016 1:35 am 
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Joined: Aug Sat 20, 2016 2:17 am
Posts: 7
Mike Yancey wrote:
Heck, I'd start from the connector and go forward.
If you have a little audio amplifier & speaker, or better a 'scopy, you can test this all the way to the grid of wherever the Audio goes in.

Not sure which schematic you're using. If you're using this one - viewtopic.php?t=63310
1. Check the audio at the input of the isolation transformer.
2. Check the output - you could be wrong-way 'round on the transformer
3. Check Pin 3 on the 6888... is there still audio?

If you hear a carrier (or it 'silences' the frequency when you power on), you're REAL close.

Oddball situations:
I have found with some setups - cheap Chinese radios - the 'headphone output' is mono, but the audio goes across the tip & ring - there is no ground.
This is fine for a plain-jane $2 stereo headphone - it PLAYS fine.
But if you feed this into your transmitter input - there is no GROUND - so there will be no audio.
I only mention 'cause it came up for me, recently.

Mike Yancey, KM5Z
Dallas, Texas


Hearing the carrier and seeing the signal meter on my receiver hit max when the transmitter powered up told me I was close. But no dice...

Spent the afternoon going through every component on the audio side. Started looking closely at the pictures Colin Ames posted and something odd caught my eye. "Q" on the detector tube. My detector tube didnt have a "Q" in the part number, it had "C" 6SC7. Pulled out my RCA tube book and found that letter makes a world of difference. Checked my tube order, yep, ordered a 6SQ7 but received a 6SC7 :evil:

Think I'm on the right track now..


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Sep Tue 06, 2016 4:47 pm 
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Joined: Aug Sat 20, 2016 2:17 am
Posts: 7
Transmitter works FABULOUSLY with the correct tube installed ;)

Rockin' out to some Louis Armstrong on my 1930's Philco. Lovin it!


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Sep Tue 06, 2016 4:51 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1129
Location: Dallas, Texas USA
Hah! Excellence!
Yes, it does. I'm planning to use it to feed baseball games (on FM) to an AM portable to listen on my porch
(when the weather turns a bit cooler). Sadly, baseball is only in Spanish in the Dallas area.

Glad to see you got it going.

Mike Yancey (KM5Z)
Dallas, Texas

Solamar wrote:
Transmitter works FABULOUSLY with the correct tube installed ;)

Rockin' out to some Louis Armstrong on my 1930's Philco. Lovin it!


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 Post subject: Re: 6888 AM broadcaster with PCB
PostPosted: Jan Sat 14, 2017 8:01 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 154
Location: Springville, NY
After completing the Lil 7 transmitter I decided to give this project a try. I ordered the board and majority of the components from Digi-Key. The 0.1uF 250v caps (ECQ-E2104KB) are backordered until March so need to find another source for those. Still need to get the tubes and sockets. Which makes me ask this question: Is there a electrical difference between the metal tubes and a tube that has a glass globe? The 6888 and 6SQ7 I have found in both versions. I prefer the filament glow of a glass tube. Any tips or advise from those that have built this would be appreciated.


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