[UK-CONTEST] Transformer Heating

[Steve Knowles]

Blowing the transformer is a really good idea if you can't afford a Henry 5k 
(or equivalent) !!

My first experience with an amplifier was with a borrowed KW1000 (how long 
ago was that??) which lasted barely the first hour of a 28MHz Phone contest 
before the mains tranny went out with an enormous bang.  Big cost to replace 
!!

Then I moved on to (my own) FL2100Z which (as I hadn't learned my lesson) 
didn't do much better, only this time I couldn't easily get a genuine 
replacement transformer.  A local company (now, alas, defunct) did an 
excellent re-design and built a new and better one for me for less than £100 
(but that was also a   l o n g   time ago).  As I left the factory with my 
new prize clutched under my arm, the last words aimed at me were "For Pete's 
sake, keep it cool!"  So for well over a decade I had an outboard 4 1/2" 
axial blower fixed to the top of the case blowing down on the transformer - 
and no trouble, no matter what I did.

A few years ago, driven by the inability of modern (Chinese) 572B tubes to 
stand high anode voltages, I moved to a Linear Amp UK Ranger 811H, which 
uses 4 tubes, rather than the pair in the FL2100Z, but at about half the 
rail volts.  This has a superbly large toroidal mains tranny and a large 
fan, and the air path is well-designed so that ALL the PA cooling air passes 
over the transformer first.  I have enormous confidence in it, if only 
because the shack warms up, but the amplifier doesn't, HI!

73

Steve  G3UFY


----- Original Message ----- 
From: "Roger Parsons" <ve3zi at yahoo.com>
To: <uk-contest at contesting.com>
Sent: Thursday, January 26, 2012 10:24 PM
Subject: [UK-CONTEST] Transformer Heating


>I was interested in David, G3YYD's comments about cooling transformers. I 
>don't think I have ever seen any amateur or commercial transmitters with 
>fan cooled transformers. Well, slight correction, some amateur amplifiers 
>have fans that vaguely waft air around on its way to the tube. However, it 
>seems a good idea and I think I will try it...
>
> BTW, the power limit in Canada is (unfortunately) not 1500W. We are 
> allowed to run 1kW DC input on CW or AM or the equivalent PEP on SSB. That 
> leads to the anomalous situation that used to be the case in the UK that 
> on CW, FM or RTTY we can run 667W output, but on AM or SSB an enormous 
> 2668W. Industry Canada is just about as interested in amateur radio as 
> Ofcom so there is zero chance of any change.
>
> 73 Roger
> VE3ZI/G3RBP
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