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 Post subject: AM transmitter options?
PostPosted: Dec Thu 07, 2017 10:57 am 
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Location: Charlevoix, Michigan, USA
I am looking for a frequency-agile AM transmitter I can use to play MP3 files over my antique radios. I say frequency agile, because at night I sometimes get interference from distant stations on the fixed frequency my 12AT6/12CS6 transmitter is set to (I built mine for 1228KHz, in hopes that the odd frequency would not get any interference. However...). The SSTRAN is now out of production, so that is not an option. Don't want to spend an arm and a leg, either. Are there any options out there?


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Thu 07, 2017 11:22 am 
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viewtopic.php?f=12&t=280783&p=2345984#p2345984

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 Post subject: Re: AM transmitter options?
PostPosted: Dec Thu 07, 2017 4:59 pm 
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If it's tuned properly, within 40-50ft of transmitter a 12CS6 should cover the background noise easily...


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Thu 07, 2017 11:32 pm 
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Location: Charlevoix, Michigan, USA
The worst problem I have with interference is with one of our local stations, especially when I am using one of my 1920's TRF sets (they actually sound better to my ear than most of my later sets, oddly enough, unless I am using my Atwater Kent horn speaker). Because they tune rather more broadly than a superhet, our local station at 1270KHz - which, believe it or not, comes in so strongly during daylight hours that you can sometimes pick it up on a crystal set just by touching the antenna terminal, with no ground hook-up - can be heard in the background, even with my 12CS6/12AT6 transmitter set up nearby with a good antenna. The station still comes in strongly at night, even after the station throttles its power back. Thus, my desire for a frequency-agile transmitter.

So again, is there one available as a kit? Or has someone designed one and published the info on how to build one? Can an older "talking house" transmitter be modified easily (I have seen some fairly cheap on EBay)?


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 2:40 am 
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Ramsey had a fairly decent unit but AFAIK they ran afoul with the powers that be, so it's discontinued... The Vectronics 1290K is apparently still being sold... My experience is it isn't as good as they make it sound but does perform somewhat acceptable... http://www.vectronics.com/Product.php?p ... =VEC-1290K

There have been some positive reports on the Talking House, but others say junk which is experience with one I had around here... They do seem to be hit or miss...


Tom


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 10:05 am 
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I had a Talking House 5 transmitter, and loved both the digital frequency display, and ease of selecting the transmitting frequency. I sold it, however, because of the background hum it continually had.

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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 2:47 pm 
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I see Vectronics (owned by MFJ) has a kit (VEC-1290K) for about $30. Wonder if it is any good...?


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 6:45 pm 
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Rich K. wrote:
I see Vectronics (owned by MFJ) has a kit (VEC-1290K) for about $30. Wonder if it is any good...?


Here is the schematic.
Image


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 7:17 pm 
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Doesn't tell me much. I know it has some frequency adjustment and antenna tuning built into it, though.


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 10:35 pm 
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Mike Toon wrote:
Rich K. wrote:
I see Vectronics (owned by MFJ) has a kit (VEC-1290K) for about $30. Wonder if it is any good...?


Here is the schematic.

Wow, Mike, thanks for posting that. It's dated 1990. Do you think that's the first use of a 386 as a modulator?

I've wondered if a simple LC oscillator would be stable enough for most ARFers' use. The trend lately is to use some form of crystal control. But if Vectronics has a $30 kit that includes antenna tuning, that might turn out to be a fine substitute for SSTrans.


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Fri 08, 2017 10:46 pm 
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Location: Arlington, TX, USA
The problem I had with an LC oscillator was the beat tone from adjacent stations would rise and fall constantly as the oscillator drifted up and down. Also there would be beat tones from distant stations on the same frequency giving low frequency tones also rising and falling with oscillator drift. If you're in an area with few stations on the dial I guess it's OK.


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Sun 10, 2017 6:12 pm 
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That's why crystal control is the way to go. Anything with MFJ on it should be regarded with some skepticism.

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 Post subject: Re: AM transmitter options?
PostPosted: Dec Sat 16, 2017 4:36 pm 
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Location: Charlevoix, Michigan, USA
Just found this kit on EBay: https://www.ebay.com/itm/AM-Transmitter-Kit/142624623282?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649. Looks promising...


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Sat 16, 2017 5:51 pm 
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Location: Crossville, TN USA
I have a couple of two-tube AM transmitters, both are octal tubes. They are missing one tube and I am not sure what that tube should be. I thought I had a paper showing the unit, but have misplaced it.


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Sun 17, 2017 12:21 am 
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Joezenithman wrote:
I have a couple of two-tube AM transmitters, both are octal tubes. They are missing one tube and I am not sure what that tube should be. I thought I had a paper showing the unit, but have misplaced it.

Being octal it's probably copy of the Zenith phono osc, those had a rectifier and probably a 12SA7... I dunno if any of those used a power transformer...

A picture would be helpful, depending on what it is, possibly may need close view of wiring to sockets...


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 Post subject: Re: AM transmitter options?
PostPosted: Dec Sun 17, 2017 4:49 am 
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Location: Crossville, TN USA
I found these two AM transmitters. One tube is the rectifier, a 35Z5 and the missing tube was a 12something or other, maybe a 12SQ7? Any thoughts on what the second tube should be? I'll have to see if I can't find the paper that came with this, but I might not. They look to be new, and I have no use for them as I have an SSTRAN and a Talking House.


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