Re: Thermal Fuse, Transformer




"Soundhaspriority" <nowhere@xxxxxxxxxxx> wrote in message
news:2o2dnUQcYNOjnLTUnZ2dnUVZ_gKdnZ2d@xxxxxxxxxxxxxxx

"Stevie D" <steve.dumouchel@xxxxxxxxxxxx> wrote in message
news:c2db1f7f-f10d-45da-8299-f193823b2c09@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I've a question as to which value 'fuse' to use in series with the
primary winding of this Technics amplifier of which the original one
opened-up. I bought two today and will wait to hear from this group
before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
I suspect I might be a little off maybe, maybe too high??? I cannot
remove the original one to verify. Any help is appreciated, thank-you.
Cheers, Steve

You partially unwound the transformer?

I don't understand the rationale for thermal fuses in transformer
primaries. Going back afew years, I don't recall they were used at all.
Yamaha preamps transitioned from a design which used discrete external
fuses to one that used the internal fuse.

Is there anyone who can supply a detailed argument why the thermal fuse
could not be omitted, replaced instead by a close-value external fuse? It
seems to me the purpose may have been to avoid the occasional spontaneous
fuse blow, but when the internal one goes, what a mess it is!

**[True story]
----
Many years ago (ca. 1985), I sold a range of audio equipment, from a range
of manufacturers, including Sansui. I refused to sell some of the Sansui
products, because I did not like the construction, which consisted of
plastic side pieces and a pressboard baseplate. The power transformer was
mounted within 1cm of the plastic side cheeks. Typical models included:
A700, A900, B77, et al. I did sell the AUD series, due to their high quality
construction and advanced topology.

A mate called into my store one day and asked for me. I wasn't available, so
he travelled to another store. The other store sold him some of the Sansui
stuff, I refused to sell. A couple of years later I ran into him at a
function. I asked him how he was going with his house rebuilding. He said
that things were progressing. I asked if the investigators had worked out
what had caused the fire that burned his house down. He said that it was the
stereo amplifier that did it.
----
It was not uncommon back then (ca. 1985) for repairers to short out the
thermal fuse, after it had failed (which it did with huge numbers of cheap
Sansui amps, due to the high operating temps of the transformers - partly
due to the poor quality of the transformers and partly due to poor
ventilation, due the pressboard baseplates).

Moral: Always replace the thermal fuse with another, similar thermal fuse.

Further and for the record: So cheap and crappy were this range of
amplifiers, that Sansui employed *no* current limiters in many of the models
in their cheap range.


--
Trevor Wilson
www.rageaudio.com.au


.

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