Power Supply questions on a Howard 400x

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Power Supply questions on a Howard 400x

Post by lhlyda on Fri Mar 03, 2017 4:22 pm

I have a few questions on terminology and theory about this power circuit on the Howard 400x made about 1937.

1) what is the component in picture with the markings TheMotoCo, Chicago, Ill?

2) Is it the component labeled on the schematic as speaker field?

3) what is the term 1000 ohm "hot" mean?

4) what should the dc resistance be?

5) the wet electrolytic was wired on the opposite side from the rectifier tube where the schematic shows it should be on the tube side. What efftect would this have?

There is no sign where it had been changed, it appears to be from the factory.

Any info or comments will be appreciated.





Last edited by lhlyda on Fri Mar 03, 2017 4:25 pm; edited 1 time in total (Reason for editing : Add pics)
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Re: Power Supply questions on a Howard 400x

Post by jerryhawthorne on Fri Mar 03, 2017 5:46 pm

The item shown in the first picture is often referred to as a cadohm resistor. Yours contains three wirewound resistors of 15K, 10K and 5K ohms as shown on the schematic just above the field coil which is part of the speaker itself.
Not certain on your question about the capacitor location, could you mark its current location on the schematic for viewing? I suspect it is fine if nothing appears to have been changed.
The hot designation on the field coil means to check the resistance after the radio has been running a while (turn off the power before checking). Resistance will change with temperature.
Best, Jerry

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Re: Power Supply questions on a Howard 400x

Post by lhlyda on Fri Mar 03, 2017 9:10 pm

Jerry,

Thx for the reply. The candohm resistor is in another location, Ive located it. From another forum, someone told me, that a power resistor may have been added in a later revision.mit is factory mounted and one end is attached to the rectifier tube, and the other is connected to the rest of the radio circuit. It is at this point the wet cap was connected. I'll try to post another picture in the next post
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Re: Power Supply questions on a Howard 400x

Post by lhlyda on Fri Mar 03, 2017 9:26 pm

here is a picture, I rechecked the circuit, it appears to be a power resistor. It reads about 300 ohms. The circuit goes to the speaker field and back into the chassis. I have googled TheMoterCo and cant find any info. BTW, the paper caps and main electrolytic have been rebuit.

Thx for the input.
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Re: Power Supply questions on a Howard 400x

Post by willy3486 on Fri Mar 03, 2017 11:57 pm

Another way of thinking on the field coil is that it acts as a electromagnet to replace the magnet in speakers. I think you are right on it being a later revision. If I am thinking correct the socket the resistor wire goes to is the 80 tube then the other wire goes to the 8 mf cap you replaced. I have seen changes like this before. I did a quick look on Nostalgia air for this radio and I didn't see any other 300 ohm resistor other than the one on the 6a7 tube.

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Re: Power Supply questions on a Howard 400x

Post by lhlyda on Sat Mar 04, 2017 8:56 am

Thx Willy, you are correct. It makes sense to put the filter past the added resistor.
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Re: Power Supply questions on a Howard 400x

Post by Bill Cahill on Mon Mar 06, 2017 2:12 am

A fair warning that if the radio originally used an 8 mf electrolytic capacitor with a field coil speaker, You will need to raise the value of that filter from 8mf to approximately 20 mf.
The field acted as a hum bucker. Therefore, you have to add more capacitance, and, likely with the second filter, as well.

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