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 Post subject: Belmont 40A
PostPosted: Nov Sat 16, 2019 9:24 pm 
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Joined: Aug Thu 09, 2018 3:00 am
Posts: 14
Hi all, working on a Belmont 40A I picked up.Have the schematic, but no parts list or wiring diagram. Confused a bit about the 4. and 8.0 condensors shown near the power supply. Are they electrolytic? If so, what is the polarity? Schematic doesnt show any polarity. So can I use electrlytics? If so what polarity do I observe / thanks, JIM


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 Post subject: Re: Belmont 40A
PostPosted: Nov Sat 16, 2019 9:49 pm 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 2015
Location: Austin, Texas
Those are electrolytic capacitors. The positive side is up. Both positives connect to the filament of the rectifier tube.
Best to stay with something around 10uF to replace the 8uF. The 4uF can be much larger like 20uF and that will reduce any hum.

It's a difficult schematic to understand with the speaker field in the negative side of the B+ supply.
At first it looks like there is no current path for the 350 ohm resistor that provides the bias to the 47 grid.
The current path is through the center tap of the filament winding so that the plate and screen current of the 47 go through the 350 ohm and produce the negative bias voltage.
Note that M means x1,000 on this schematic.

Jay


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 Post subject: Re: Belmont 40A
PostPosted: Nov Sun 17, 2019 6:27 am 
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Joined: Aug Thu 09, 2018 3:00 am
Posts: 14
Thank you Jay. That helps alot. One last section of this radio I am struggling with. I am going to try to attach a picture of the section. There are 2 brown tubular items that I think are 25K ohm resistors. Never saw a resistor like that before. Is that what they are? What can I replace them with? 25K 10 watt power resistors? Also , in the shematic right in with that circuit are supposed to be three .1 uf capacitors hooked to ground in between the string of three 25K resistors. Where are they? Cant find them. Thanks, Jim


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File comment: 2 brown tubular items, 25K resistors? where are the .1 uf caps ?
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 Post subject: Re: Belmont 40A
PostPosted: Nov Sun 17, 2019 11:00 am 
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Joined: Feb Tue 24, 2009 8:20 am
Posts: 10800
Location: Aurora Colorado
I think that the 2 brown tubular items are "cub" brand capacitors. They are paper and foil wrapped around the wood form.
The labels were fragile, cellophane maybe, so, might be long gone.

They look like ones I have seen , and they have enough size to be a couple of your .1 mfd caps.Lift one leg, and look underneath
to try and see a label, and see if they connect between your resistors.

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 Post subject: Re: Belmont 40A
PostPosted: Nov Thu 21, 2019 2:48 am 
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Joined: Aug Thu 09, 2018 3:00 am
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Those mysterious brown tubular items continue to confuse me. Removed them completely and could find no markings on them at all. At each end is a metal tab that comes out of the capacitor and goes directly to ground. Kind of riveted in. Im not sure if one item constitutes 2 capacitors or what. Anyone ever seen them before? thanks


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 Post subject: Re: Belmont 40A
PostPosted: Nov Thu 21, 2019 6:09 am 
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Joined: Feb Tue 24, 2009 8:20 am
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Location: Aurora Colorado
It looks like the one on the right connects to a pin on the tube that has a 57 next to it. And it looks like the

wire at that point goes to the tube above it. See what is connected to those pins, and that will

tell you what they are.

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