trobbins wrote:It may actually be worth checking the OT turns ratio to confirm the 15 ohm marked windings are for 15 ohm loading.
As there are two separate windings, one could ambiguously presume that loading each winding with 15 ohm was the design intent, but that would then present an 8 ohm loading to the primary. So the windings could actually be 8 ohm windings, and meant to be used with 15 ohm loading on each winding.
Note the 4 secondary windings on the Sowter page.
Logically, they must be 1 ohm each, but all 4 paralleled is still 1 ohm.
In the same way that connecting the 2 x 120V primary windings of a worldwide PT in parallel doesn't change the secondary voltages.
So putting identical windings in parallel doesn't change the ratios etc.
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JMFahey wrote:Won't comment on other problems, but as a side note, paralleling 2 "15 ohms" windings will not turn them into a 7.5 ohms one but still 15 ohms (windings are not resistive and all what matters is voltage, which does not change) ,at most it's still a 15 ohms winding but has 1/2 the DC resistance, so it's slightly more efficient ... but nothing else.
Thanks for the explanation, that's one to file away in the memory.
pdf64 wrote:So putting identical windings in parallel doesn't change the ratios etc.
The comment about checking the turns ratio of the 15 ohm windings was more related to the PA application for the amp, where it could be quite practical and convenient to connect each of the 15 ohm windings to a separate 15 ohm speaker column for some audience venues.
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