power transformer question

[jfjp kruijs voorberge]

hello
Can I use a universal power transformer out of a hallicrafters S-40 AU into
an SX -100 ? The power consumption of the S-40 is less than that of the
SX-100 so I am afraid that is getting to hot or could it deliver the extra
watts ?
Thanks in advance
hans

[COLIN LAMB]

Hello Hans:

Using a power transformer from a set that consumes less power can be an
invitation to failure -but it can be done if there is no other option.

In most receivers, the voltage out is similar. The problem for a
transformer is that when the load increase beyond design, heat will rise.
Most receivers are already pretty warm inside.

Compare the total power consumed by the two transformers in their respective
receivers. If the replacement power transformer is something like 15% less
power, it can be a candidate for swapping. But, there are a couple of
things I would do. First, replace the rectifier tube with a solid state
version (including resistors to drop voltage equal to the drop by the
rectifier tube. Secondly, use a variac to keep the line voltage down to 110
vac (or 220 in Europe). Third, ad a small muffin fan to remove heat from
the radio.

Of course using a proper transformer is the best solution - but sometimes it
is necessary to improvise. The SX-100 is a much more valuable receiver,
however, and inserting a transformer from an S-40 will decrease the value.
You might be able to find a transformer from a SX100 or SX-96, which would
be a better solution.

Many years ago, I oten did things like that because that was all that was
available.

Good luck, Colin K7FM

[Kenneth Scharf]

If you don't use the filament windings from the smaller transformer and
power the tube filaments from an added filament transformer this will
reduce the load on the smaller unit. If the set used a rectifier tube
with a 5v filament either provide a second external filament transformer
for that or replace the tube with silicon diodes.

[Tim Wescott]

It will get hotter than it gets now. Assuming the output voltages are
the same as the one you're replacing, it'll get hotter as the square of
the current rise.

You say it's a "universal power transformer" -- does that mean that it's
not what originally came in the S-40? If it isn't original, is it
specified heavy enough to go into the SX-100?

If you're inspiration limited rather than money limited, Antique
Electronics Supply has power transformers -- they ought to have something
that'll work, and may even have something that'll fit. http://
www.tubesandmore.com.

--
www.wescottdesign.com

[Kenneth Scharf]

Check these guys out: http://www.oldradioparts.com/
They have lots of new, used, and surplus power transformers for radios
at good prices. Note that they don't update the web page inventory too
often so email them to ask if the unit you want is still in stock and
give several alternates. They give quick service, I've bought stuff
there before.

[COLIN LAMB]

I think universal power transformer simply means it is a transformer
designed for both 120 and 240. Purchasing a Hallicrafters with such a
transformer was available for users in the rest of the world.

Colin Lamb K7FM

[Tim Wescott]

Oh, _that_ kind of universal.

--
www.wescottdesign.com

[jfjp kruijs voorberge]

hello
Many thanks for all your kind reactions
My only question was if I could use the universal power transformer out of a
not used S-40 AU into a SX-100 to make the SX-100 all hallicrafters again .
It is now working very good with a non hallicrafters transformer
I decided not to change anything at all because the risk that something goes
wrong is to great
thanks again
hans

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