21-03-2019, 11:55 AM
(19-03-2019, 08:56 PM)markandrewberry Wrote: I was wondering if any of the range of '100 Volt' audio transformers sold by CPC might be suitable
No, Mark. A 100V line transformer would be used with a public address or similar amplifier feeding a range of remote speakers. The high voltage minimises losses in the distribution wiring and each speaker has its own line matching transformer, usually with several taps so that the appropriate power level required at that particular location can be selected.
Nothing at all like the output transformer required for anything you are ever likely to come into contact with.
The ratio of the output transformer is the square root of RL (the valve's optimum load impedance), in this case 3k, divided by the speaker's impedance which with sets of this vintage is usually ~3 ohms.
Thus we have 3000/3 = 1000 and √1000 = 31.6. If it is a 4Ω speaker, the ratio would be 27.4 so, ideally, you are looking for a transformer with a turns ratio of ~30:1. However, for the moment, a suitable mains transformer as suggested by Jeffrey will suffice to get the set working. If it has several secondary taps, a 9V tap will be the closest to what you want.
