[AMRadio] would like to build a little homebrew project

Greg bluebirdtele at embarqmail.com
Tue Jul 31 11:36:37 EDT 2007


You are talking about a fairly big and expensive transmitter.  If this is 
your first one, it's going to be a long process.
I think the first thing you should settle on is what tube(s) will make up 
the PA.  Then you need to figure out what the mod transformer requirement 
will be. Mod transformers are spec'd for impedance and power capability. You 
need to find out how to electrically match the mod transformer to the PA. A 
good source of mod transformers is Ebay. Particularly the multi-tap 
universal output types that companies like Stancor used to make.
The WWW has websites with JAVA calculators that can compute things like pi 
net values for a given tube or tubes.
For what it's worth, I would not build the 3-400Z up due to the expense, I 
would go with the 811A's.  The voltage won't exceed 1,200 vdc and that will 
help keep expenses down overall for parts.
The last big part is finding a transformer that will power the thing.  This 
is a real important point.  Too little transformer will literally make the 
rig unuseable and too much is money and space tossed out the window. Another 
thing you might try is to get your flea market parts/ resources in order. 
You can save a ton of money recycling someone elses bits and pieces.
The best thing you can do for now is get on the web and start tracking down 
the basic information for pi nets, AM power supplies, tubes etc.  When you 
have settled on what you want to do let me know and I will look into the old 
archive for a suiitable match in circuitry.  Hey, by that time you may have 
already drawn up your own!
Kinston NC
----- Original Message ----- 
From: "Jason Buchanan" <jsb at digistar.com>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Tuesday, July 31, 2007 9:19 AM
Subject: Re: [AMRadio] would like to build a little homebrew project

> On Jul 31, 2007, at 12:13 AM, Greg wrote:
>> What power level are you thinking about?
> I've got some 3-400Z spares and sockets...  I think i'm limited  mostly by 
> the cost of the transformer(s).  An 811A project wouldn't  be out of reach 
> in terms of the cost of the tube and a plate  transformer.  Ideally i'd 
> like to build something that produces the  full legal limit but I think 
> that would be cost prohibitive and  unwise until I get something smaller 
> under my belt. hi hi
>> What features and what is the modulation scheme?
> 160 meters, T/R switching relay with receiver muting for Drake R-4, 
> possibly xtal controlled for fixed frequency at 1885KC for example.
>> I have a bunch of older left coast and ARRL handbooks that may have  what 
>> you are looking for. I may be able to locate something for you  and scan 
>> it to you.
> That would be swell.
> I'm fairly comfortable building HV supplies, etc. but i'm completely 
> unfamiliar with how to calculate what size variable capacitors to use  for 
> tuning, tank coils, etc.
> Thanks!
> --
> 73 Jason N1SU
> http://n1su.com/
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