Model 90 (45 p-p) - Printable Version

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Model 90 (45 p-p) - TimG - 05-15-2024

On my model 90 the output transformer is bad.  I have a Hammond P-T291 laying around. Will ths work?  8watts enough?

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RE: Model 90 (45 p-p) - morzh - 05-15-2024

Unfortunately. I forgot what the impedance of the K speaker, but it is 0.2 or 0.3 Ohm, not 4 or 8 ohm.
0.3 ohm means that if you use it with 4 ohm winding, your load will look like 670 Ohm, and not like 9 kOhm. There will be very little power output into it.
The 125 Hammond does the job.

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RE: Model 90 (45 p-p) - TimG - 05-15-2024

0.7 impedance. Does anybody know the wattage required here?

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RE: Model 90 (45 p-p) - morzh - 05-15-2024

So it is 0.175 times 9K, which is 1.6K.
You want around 8K-9K.

3W would be sufficient for your power for the transformer.
125B Hammond is sufficient electrically.
If you find out the size and the distance between the holes is closer to 125C, use that one. I think I used 125C for K speaker.
You want to use 2 & 3 leads for the Voice coil; this at 0.7 Ohm will give you 9K, which is about what you need.
Though 3 & 4 will also work.

https://www.hammfg.com/electronics/transformers/audio/125a-125e

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RE: Model 90 (45 p-p) - TimG - 05-15-2024

Thanks perfect!

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