[AMRadio] XFMR info needed


Greg Mijal bluebirdtele at embarqmail.com
Thu Sep 30 17:08:51 EDT 2010


The only way you are going to know for sure which transfomer to use is to 
build up the supply on a table top and load it down with a  hi-watt load 
resistor. I build power supplies pretty frequently and this seems the only 
way to really know what the supply will do or not do.  Manufacturers print 
funny stuff on the side to indicate what the transformer is rated at.  Some, 
like Stancor have the typical 260-0-260 marked on the side. Meaning 260 p-p 
each side of the center tap.  Others, particularly military stuff have odd 
markings like 800v 300ma.  Those are the ones you have to run up on a load 
resistors to figure out what it really does.
Anyway, good luck.  Power supply building is part science and part witch 
craft.
73's
Greg
WA7LYO
Kinston NC
----- Original Message ----- 
From: "CL in NC" <mjcal77 at yahoo.com>
To: "AM radio" <amradio at mailman.qth.net>
Sent: Thursday, September 30, 2010 1:53 PM
Subject: [AMRadio] XFMR info needed


>I recently picked up a Heath HA10 Warrior amp to finish out my Heath 
>station.  Come to find out the PS had been gutted, and rebuilt with only a 
>power XFMR. a full wave bridge rectifier, and about 16uf of filter, which 
>put over 2KV on the plates of the 811's in standby, it pins the meter out. 
>The missing swinging choke must have met the same demise as the power XFMR 
>considering the amount of blackness that was left under the chassis.
>
> I got some good info here on the UTC S-45 'Special Service' transformer 
> currently in the amp, but, unless I looked at the specs wrong, it is rated 
> at only 200ma CCS.  The original Heath was around 3KV at 500MA with a full 
> wave rect., a swinging choke in the center tap and 8uf of filter.
>
> Was digging in my stuff and found a nice xfmr with a 1100V at 700ma center 
> tapped secondary, some government surplus find from years ago.  The thing 
> is, this surplus transformer is somewhat smaller than the UTC S-45, which 
> has a 750/900 center tapped secondary and only 200ma rating.
>
> So, is that UTC 200ma CCS rating wrong, did I read it wrong, or did UTC 
> spec out their xfmrs extremely concervatively?  I have not put RF to this 
> amp yet to see how much  the voltage sagged under load, but in it's 
> present form, the regulation won't be there for AM operation
>
> Thanks for any help,
>
> Charlie, W4MEC in NC
>
>
>
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