[AMRadio] Power Transformer as Mod Transformer (was: Seventy Fiver)


John Coleman jc at pctechref.com
Thu Sep 24 10:32:04 EDT 2009


That is a great article Brian, and Lee.  I have done this a long time ago.
They work really well especially with the choke.  They also make pretty good
output XFMRS for HiFi and PA.  The old 200 watt XFMRs we once saw in the old
TVs are not as available as they once were.  

Prior to the Switch Mode solid state supply that Modern TV use, but after
the big XFMRs and the 5U4s, there was a lot of constant voltage XFMRs in TVs
especially the hybrids.  These are recognizable because they were always
accompanied with a 2-10 MF 600V capacitor in a can, possibly oil filled,
used on the saturation winding of the XFMR.  I have found them to make very
good regulators for RCVRs, VFO, etc.  They will maintain the supply voltage
constant to the VFO plate and heater even if the mains drop to 100V when a
big rig is key to XMIT.  This way you don't slide up the band while XMITing.

John, WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Bry Carling
Sent: Thursday, September 24, 2009 4:50 AM
To: glowbugs at piobaire.mines.uidaho.edu
Cc: FLBOATANCHORS at yahoogroups.com; Discussion of AM Radio in the Amateur
Service
Subject: [AMRadio] Power Transformer as Mod Transformer (was: Seventy Fiver)

There is a great article on how to use power transformers like that - as 
a mod transformer - available on line for free - by Tim, WA1HLR

I hope it helps you - 

http://www.amwindow.org/tech/htm/tvtomod.htm

LEE, W0VT writes:

> I went to Lowe's this evening and picked up some oak lumber to build up
some "Slat Board" 
> Transmitters. (They sell oak down to 1/4 inch thick to be used for the
"slats". I plan to screw the 
> slats to the main oak end panels with brass screws and then stain and
polyurethane the wood. I 
> plan to build up one chassis as a 6V6 oscillator with pi-net. Another with
a 6AG7 with pi-net. 
> Then compair the output of the two plus check crystal current on both of
them. Then I plan to 
> build up another one with a 6AG7 osc and 6L6 amp with pi-net and plug in
coils. Then I plan to 
> build power supplies for these on slat board chassis and maybe use 5R4
rectifiers as I have some 
> of these around here. Then maybe a modulator for the 6AG7/6L6 rig. For a
modulation 
> transformer I am thinking of trying a 70 volt or 25 volt line transformer
or/and a power transformer 
> having it's core "restacked" in E and I configuration with a gap between
the two. The projects 
> won't cost much and I think they will be great looking. I'll use broadcast
band variable caps in the 
> pi networks. (Duals for loading and singles for the tank circuit.). Maybe
use some rigid clear 
> plastic tubing over old tube sockets for the plug in coils. 
> 
> Lee, w0vt 
>     ----- Original Message ----- 
>     From: Charlie , W5COV 
>     To: glowbugs at piobaire.mines.uidaho.edu 
>     Sent: Wednesday, September 23, 2009 9:04 PM 
>     Subject: GB> Seventy Fiver 
>     Group , the topic came up a while back with thoughts of building a 75
meter version 
>     of the Twoer etc. Heath line . 
>     
>     Did it fall by the way , because of a lack of interest , or did anyone
do any type of 
>     development on something like this ? 
>     
>     I am ALWAYS looking for a glowbug project to build , that isn't real
complex and 
>     won't break the bank. 
>     
>     A transceiver to put on the air would be a nice project . I have a
bench overflowing 
>     with homebrew transmitters , mostly CW . 
>     
>     Being on a fixed income , I like projects that parts can be readily
obtained for at 
>     cheap prices . 
>     
>     With my medical problems , I lack the design ability , that I used to
have . The 
>     medications and disease cause a technical medical term called "brain
fog" . 
>     
>     So I depend HEAVILY , almost exclusively ,on other peoples designs . 
>     
>     So if you know of a simple transceiver design that glows and is AM ,
please point me 
>     to it . 
>     
>     Thanks for allowing me to be a part of the best group I belong to !! 
>     
>     73, 
>     
>     Charlie , W5COV 


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