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Old 13th November 2012, 04:23 PM   #1
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Default 40's tube receiver question

Hi, I have a 1947? radio that will still operate but has 60hz hum through the speaker. I realize the old paper-wax capacitors are suspect, but other than the hum, the radio operates very well. Even in it's current state it has much more sensitive reception than the solid state radio I have in my shop. Do I need to do all the caps? Electrolytic caps are fine for replacements?
Here's a couple of pics:
IMG_0350.jpg
IMG_0351.jpg
IMG_0352.jpg
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Old 13th November 2012, 04:34 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

I note the label seems to imply it can run from DC ? use a DC supply ?

rgds, sreten.
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Old 13th November 2012, 04:50 PM   #3
kevinkr is offline kevinkr  United States
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First I need to mention that this radio is directly mains operated and can be EXTREMELY hazardous to work on. Please go and purchase an isolation transformer on eBay before going any further.

All of the electrolytic filter caps and paper (waxy looking caps) need to be replaced. Most of these parts can be purchased from places like Antique Electronic Supply LLC and Radio Daze, LLC. - Antique Radio Parts & Service

Radio Daze has a selection of multi-section caps here: Multi-Section

In addition you should add a line fuse for safety, and make sure that the paper cap between AC line and metal chassis if present is replaced with an equal value ceramic or film Y cap.

See here: ABC's of Safety (Interference Suppression) Capacitors for Tube Radios
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Old 13th November 2012, 04:54 PM   #4
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by sreten View Post
Hi,

I note the label seems to imply it can run from DC ? use a DC supply ?

rgds, sreten.

Better to replace all of those 65yr old capacitors IMO..
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Old 13th November 2012, 05:21 PM   #5
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Thanks for the links Kevin. I'll get the transformer on order.
This radio has no line filter capacitor, though it looks like it should have according to that article.
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Old 13th November 2012, 06:29 PM   #6
TheGimp is offline TheGimp  United States
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Be careful you get a true 'isolation transformer', not an 'auto-transformer'. The auto- transformer has no isolation between primary and secondary.
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Old 13th November 2012, 10:26 PM   #7
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I'm having trouble finding a multi section tubular cap like the one in the radio. It's a 60/30 uf, would a 47/33 uf be adequate?
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Old 14th November 2012, 12:09 AM   #8
benb is offline benb  United States
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Quote:
Originally Posted by sreten View Post
Hi,

I note the label seems to imply it can run from DC ? use a DC supply ?

rgds, sreten.
It's obviously an "All American 5" radio, and you can you can Google that name and find schematics and descriptions online. It runs directly on the 120V AC line, and will also run on 120V DC with the correct polarity so that the current goes through the half-wave rectifier tube to give plate voltage to the other tubes. 120V DC was rare, but I heard decades ago it was available on cruise ships.
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I'm having trouble finding a multi section tubular cap like the one in the radio. It's a 60/30 uf, would a 47/33 uf be adequate?
That should be fine, as electrolytics back then were +/- 20 percent on a good day.
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Old 14th November 2012, 12:12 AM   #9
kevinkr is offline kevinkr  United States
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Here is a possible option: Capacitor - Electrolytic, 33/33/47 F @ 160 VDC | Antique Electronic Supply LLC you can wire the two 33uF sections in parallel for 66uF, and the second section is 47uF.. Should result in a quieter radio..

I suspect one of those horrible paper caps is connected directly from one side of mains to the chassis - most unusual if this is not the case.

Make sure you get an actual isolation transformer as noted in a previous post, small medical grade units are cheap on eBay and will fit the bill nicely.
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Old 14th November 2012, 12:16 AM   #10
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by benb View Post
It's obviously an "All American 5" radio, and you can you can Google that name and find schematics and descriptions online. It runs directly on the 120V AC line, and will also run on 120V DC with the correct polarity so that the current goes through the half-wave rectifier tube to give plate voltage to the other tubes. 120V DC was rare, but I heard decades ago it was available on cruise ships.

<snip>
Manhattan had 110VDC in some neighborhoods well into the 1950s, as did a number of other places in the USA that were electrified late in the 19th century. Equally odd was the 25Hz power used in upstate NY and parts of the midwest until around the same time. (I have an Atwater Kent radio that was designed for 25Hz power, must have buzzed a bit although it is fairly quiet on 60Hz..)
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