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M1BYT > NEED 28.07.01 09:25l 62 Lines 2699 Bytes #999 (0) @ EU
BID : 128981M1BYT
Read: GUEST
Subj: Re: Info please (chokes)
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Sent: 010727/2250Z @:GB7FCR.#16.GBR.EU #:58671 [Blackpool] FBB-7.03a $:128981M1
From: M1BYT@GB7FCR.#16.GBR.EU
To : NEED@EU
G4MRU Opined with considerable skill:-
> Im about to start building a GLOW BUG Transmitter. I've got two good
> circuits to go at but I need a little help before starting. First,
> I've got a transformer but its 350 - 0 - 350 What is needed is 300 -
> 0 - 300. How can I get over this!.
Hi Pete,
Depending how the tranformer is built and wound, you might be able to
dismantle it and remove a suitable number of turns from the each leg of
the secondary (see how to work out how many to remove, below).
A second option might be to use an additional tranformer with several
tappings on the primary, as an auto-tranformer. Connect the mains to 0v
and the 250v and connect your original transformer between 0v and
perhaps the 210v tapping will give something closer to 300v. Watch out
for the current ratings though!
RS Components used to sell DIY transformer kits in various VA ratings,
to enable you to roll your own.
And finally you could perhaps find a transformer of both suitable size,
which had not been doped, and strip/rebuild that.
The iron laminations are either alternate T's and U's, or W's and I's.
I have done all of the above in the distant past, and I seem to remember
working on a figure of around 7 turns per volt, but perhaps someone
could confirm this. I used to wind them with a block of wood fitted in
the former, through which I drilled a hole for a bolt. Put the end of
the bolt in hand drill which is held in a vice. You then get someone to
crank and count, as you feed the wire onto the former.
An easy way to determine the turns per volt on a ready built
transformer, is to simply add an extra winding of perhaps 20 turns,
power the tranformer up and measure the voltage developed across the
additional winding. Turns/measured volts, gives you the existing turns
per volt of the transfomer.
Whatever you do, don't consider going to a transformer winder to have
one specially wound. Custom built tranformers are very, very expensive,
which is why I learnt to roll my own.
ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
º 73 from Harry, M1BYT @ GB7FCR.#16.GBR.EU.GBR º
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º Museums | IMW 2002 http://www.imw.f2s.com º
º Event | NMW 2001 http://www.qsl.net/m1byt º
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º QTH: Garforth, W. Yorks.. º Timed 23:48 º
º harry_m1byt@ntlworld.com º 27 Jul 2001 º
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