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 Post subject: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Mon 27, 2012 3:02 pm 
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Location: Charlevoix, Michigan, USA
I have been doing some thinking, and I have decided I would like to build a vintage (pre-WWII, preferably) transmitter for phone. I have a General-Class license (KC8MWG), but I'm not much into CW (I admit, I learned just enough to get my license upgraded). Let's face it, I'm a rag-chewer at heart, and I'd rather talk than tap a key. Since most of the AM amateur activity I have heard has been on 160 meters, I'd like to build my transmitter for that band (or, barring that, 75-80 meters or wherever the second-highest concentration of AM rag-chewers happens to be now). Are there any plans, schematics, etc. that are readily available for a project like this?


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Mon 27, 2012 3:30 pm 
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Location: Madison, WI
The construction of 1920's telephony transmitters is not too easy. Several important innovations had not occurred yet, namely class B modulation, electron coupled oscillators, and modulated class-C tetrodes.

The lack of class B modulation means than one has to either use grid modulation (sounds like crap) or Heising modulation. Heising modulation requires the use of a large class A audio tube which must put out audio power approximately equal to 1/2 the modulated tube's DC input power. This requires large triodes with low plate resistance such as 211, 250, 842, 845, 849, and 851. It just so happens that these tubes are also appreciated by audiophools so they are very difficult to find cheaply.

Because of the extremely low efficiency of Heising modulated stages, it was typical to follow them with class B linear amplifiers using such tubes as 204A, 852, 860, and 861.

I suggest building a 1930's type transmitter rather than 1920's unless you are up for a challenge. A big factor for finding a schematic is how much power do you want?


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Mon 27, 2012 3:41 pm 
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Location: Charlevoix, Michigan, USA
Well, I'd like at least 100 watts or so - that is what most of my modern equipment is capable of without a linear amp hooked up. 50 watts minimum. Of course, if I had to go low power, I'd then have to find plans for an amplifier of the same era...;).

1930's does sound like the better option, due to tube availability. Darn those audiophools, anyway...


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Tue 28, 2012 12:53 am 
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Location: aston, pa, usa
http://home.comcast.net/~filebay1/Cunni ... _30_50.pdf
------------------------------------------------------------------------------------------------------------
I thread-jacked this from the Bolgarian thread on homebrew. May not apply?

_________________
"All glory is fleeting" - George Patton
KB3QNN 73


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Tue 28, 2012 3:27 am 
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Location: Charlevoix, Michigan, USA
Mmmmm... thanks, but not really it. I'm looking for an actual "build-it-yourself" article from the 1930's that I can work from.


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Tue 28, 2012 3:33 am 
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For 1929 style, an 852 modulated by an 849 would give 140 watts. Alternatively, a class B linear using PP 860's or 203A's would put out about 80 watts.

If a 1930's design is desired, these documents could be perused for a circuit which best matches with your junk box:
http://www.tubebooks.org/Books/arrl_1936.pdf
http://www.audiophool.cjb.net/Misc/XmtrGuide.pdf


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Tue 28, 2012 4:30 am 
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Joined: Aug Tue 30, 2011 11:25 pm
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Location: Charlevoix, Michigan, USA
Well, matching to my junk box is a moot point. I really don't have any vintage components suitable for such a project, so I would have to beg, borrow, or buy what I need depending on what I ultimately decide to build. I have no filament transformers, few tube sockets (and the ones I have are all octals or miniatures), very few (if any) suitable tubes, etc. In other words, I would be starting from ground zero, buying those components I can't make myself as I happen to run across them (and then only if I can afford them when I DO happen to find them). This may end up being a several years' long project due to having to accumulate components. And I REALLY want this to be for 160 meters, as I have NO equipment at the present that is capable of transmitting on that band, in any mode whatsoever (my HF transceivers only cover 80-10 meters, plus I have a couple 2 meter FM transceivers and a 6-meter all-mode).

The 1936 ARRL handbook is a good start, but I found myself getting confused by it - are you supposed to build a transmitter meant for CW, then add an audio exciter, or what? I REALLY want to find just a simple, step-by-step "Here is your components list. First, solder component "A" to component "B". Wind coil "C" on a form of this-and-such diameter with this-and-such wire gauge, this-and-such many turns", etc. straight-forward and simple and easy to follow building project article. I do best when I can just follow a straight-forward set of instructions without confusing details in between.

Receivers are SO much easier... :?


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 Post subject: Re: 1920's or 1930's amateur phone transmitter plans wanted
PostPosted: Feb Wed 29, 2012 2:44 am 
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Joined: Apr Tue 27, 2010 12:02 am
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Location: Madison, WI
The 1936 ARRL handbook is laid out that way since in the 1930's transmitters were built in a modular fashion. You would have the power supply(s), modulator+speech amplifier, and exciter + PA each on their own chassis. For larger transmitters the modulator and PA would be on their own chassis as well.

As far as step-by-step instructions, you're not likely to find anything much better than the ARRL handbooks.
If coil details are not included, this is a good website for designing them: http://www.k7mem.com/Electronic_Notebook/inductors/coildsgn.html#Design_Cons
160 meters is not a problem, appropriate coils could be wound for almost any design.

On the first page of this RCA Ham tips there is a transmitter schematic which looks relatively inexpensive and simple: http://n4trb.com/AmateurRadio/RCA_Ham_Tips/issues/rcahamtips0101.pdf It should put out 100 watts in ICAS. A modulator is not shown but a pair of 807 or 809 would work.


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