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Old 16th Jul 2019, 1:47 am   #3
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
Posts: 2,632
Default Re: "Matching" transformer.

Originally Posted by Diabolical Artificer View Post
I'm guessing in the 50's most speakers were 16 ohm and the "new" transistor amplifiers of the 60's early 70's were designed for a nominal 8r speaker Z so maybe these were sold then to save loss of power Op or similar.
My recollection is that it was considered unwise to use these kinds of speaker impedance matching transformers with early solid-state amplifiers. I am not sure about this, but one potential problem may have been that at very low frequencies, they offered only a very low impedance to the amplifier, not a problem with most valved units but potentially destructive for some solid-state units.

I suspect that a major use for these transformers in the 1950s and 1960s was in connecting say a 15-16 ohm speaker of the hi-fi type to the external speaker outputs of typical radio receivers and radiograms, which were typically designed for speakers in the 2.5 to 3 ohm range. With limited AF power available, often around 3 watts, impedance matching was worthwhile.

Some of the Wharfedale cabinet speakers of the era were intended for such use as well as with hi-fi systems. This advertisement for the W3 is indicative:

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The W3 was a 15 ohm speaker, so use of the WMT1 autotransformer would have been advisable when it was to be fed from a domestic radio receiver optimized for say 3 ohms.

Originally Posted by Diabolical Artificer View Post
One last thing, I had a trannie PA amp that has an OPT between OP stage and spkr terminals, one sec for 100v line but also for 4 and 8 ohm spkr's, it sounded superb.
A classic example of a transistor power amplifier equipped with an output transformer intended to match a wide variety of loads was the Quad 50E.

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