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Any way to upgrade this circuit? (V. 40's phono amp.)
Any way to upgrade this circuit? (V. 40's phono amp.)
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Old 7th May 2009, 09:14 PM   #11
ethermion is offline ethermion  Antarctica
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Quote:
Originally posted by IDSKoT


The voice coil was actually .5 ohms, not 3.2 (or 3).
Try disconnecting the speaker and measuring again. 0.5 ohm sounds right for the speaker tap on the transformer. You cannot measure the speaker if it is connected to the transformer as the DMM will report the resistance of the speaker in parallel with that of the transformer winding.
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Old 8th May 2009, 12:23 AM   #12
ethermion is offline ethermion  Antarctica
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Quote:
Originally posted by Eli Duttman

The tube heaters are wired in series. That object you are trying to identify may be the dropping resistor that "eats" the difference between the 85 V. the tubes consume and the AC mains voltage.

Eli is probably right. The can that looks like a capacitor can is a dropping resistor. The tube heaters eat 150ma of current, and a 200 ohm resistor will drop 30 volts at 150ma. 50 + 35 + 30 = 115V, which was what you would get from the wall. So the 200 means 200 ohms, and the 630 means... something else.

Primitive little thing. Sort of the least turntable your money could buy.
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Old 8th May 2009, 12:44 AM   #13
astouffer is offline astouffer  United States
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Quote:
Try disconnecting the speaker and measuring again. 0.5 ohm sounds right for the speaker tap on the transformer. You cannot measure the speaker if it is connected to the transformer as the DMM will report the resistance of the speaker in parallel with that of the transformer winding.
DC resistance and impedance are two very different things.
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