[Amps] filament transformers

[Carl]

Good points Bob, its been decades since I tried to get the last 
lamination back in! With homebrew almost a lost art in the USA Ive found 
most of my LV needs at hamfests for very little money. A find 2 weeks 
ago looks like it was built for a pair of 304TL's and the vendors asking 
price was $5 which even I couldnt argue with!

NIB tubes and USA Johnson sockets have also been obtained at very low 
cost over the past 6 months so now its time to start laying out the next 
Class C  AM amp.

Surge suppression isnt necessary on ham size indirectly heated filaments 
(8874, 3CX800, 8877) and are not discussed in the full Eimac spec sheets 
or Care and Feeding. Now, when you are getting into tubes with handles 
that is a different story.

Carl
KM1H



----- Original Message ----- 
From: "robert briggs" <vk3zl at bigpond.com>
To: <amps at contesting.com>
Sent: Saturday, May 16, 2009 4:53 AM
Subject: [Amps] filament transformers


>
>
> What has happened to "roll your own" custom filament transformers? I
> have never purchased a commercially made filament transformer after
> building more than 40 amplifiers over 25 years....I still roll my
> own...There are plenty of sources of suitable transformers including
> older type video recorders small TV sets and a few other redundant
> pieces of  old electronic equipment..Once you find a transformer which
> is appropriate for the job at hand all it takes generally is the
> patience to disassemble it and rewinding it with  appropriate  size 
> wire
> for the job...I always  wind an extra half volt or so and use a 
> dropping
> resistor in the primary to obtain the correct voltage at the tube
> pins....This resistor also acts as a surge protection for inrush 
> current
> on switch on...I also rewind these transformers for relay and control
> voltage sources....Cheaper than buying them and more reliable as you 
> can
> set them up exactly as you want them..
>
> 73....Bob VK3ZL..
>
>
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