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Old 15th Jul 2019, 4:03 pm   #2
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 5,776
Default Re: "Matching" transformer.

I think you have virtually answered your own questions!

Speaker isolation transformer - to provide isolation from a live chassis item to an external speaker. (Many of these won't meet current safety standards, but almost certainly nobody has died yet as a result of insulation failure).

Matching transformers would match, say, a 15Ω loudspeaker to an amplifier designed for 3Ω. Impedances in common use are 3Ω, 8Ω, 15Ω but there is also the 100V standard where a matching transformer might be used to match an 8Ω speaker to a 100V line at 10W.

The output transformer in your valve amplifier is of course a matching transformer, but to avoid confusion it would probably be referred to as an "output transformer" rather than a "matching transformer."
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