So I set the wayback machine for the late '30's, and...

Jeff Gehring

Gold Supporting Member
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So I set the wayback machine for the late '30's, and upon arrival, found this curious component in a National Dobro Amplifier of the period. It's the first one I've come across, but then I don't usually work on stuff this old! The thing looks like a log of smoked gouda with terminals on it...

View media item 50161
It's a multisection box cap, (as opposed to a can cap) containing what used to be two 8uF cap sections and one 2uF section...
 

neteraser

Member
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1,993
"Dobro" means "good/goodness" in Russian. :) Just saying...
Congrats on a new rare vintage amp!
 

joelster

Silver Supporting Member
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3,691
I've got a few box caps that came out of Bell & Howell Filmosound amps. They all test perfect... Every section.
 

jthomas666

Member
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1,065
Over on OffsetGuitars a guy was asking questions about a 1930's Gibson amp with a couple of those things. I figured that they must be caps pf some kinds. Here's one of his pics. He was asking about the codes on the resistors. I wasn't much help, but figured that they probably are coded like dogbone resistors.

15726240_10210822742502888_6404039358314883785_n.jpg
 
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Jeff Gehring

Gold Supporting Member
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7,667
Those look like the body-end-stripe code: those 100k resistors for example--body = brown = 1, end = black = 0, stripe = yellow = 4. So that parses out as 10x10^4 or 100k...
 

jthomas666

Member
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1,065
Right. I found this, which I'll include here in case someone else is interested:

http://www.philipstorr.id.au/radio/technical/Resistors.pdf

Page 7 says:
<snip> Resistors made during the 1930's use a different colour marking system. The colours are read in the sequence
Body, Tip, Spot (also referred to as Body, Tip, Dot).

The colours themselves represent the same values as in the modern code in the table above. These resistors are
sometimes referred to as “Dog Bone” resistors. The resistance value of the resistor in figure 1 is read by the Body, Tip Spot method as 250,000 Ohms. The fourth band is the same colour as the body colour and so the tolerance is
unmarked and is 20 %. In figure 2, band B is Grey and band 10 is Silver making this an example of a 10% tolerance resistor of this type. <snip>
 

joelster

Silver Supporting Member
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3,691
Not sure actually. Just tested for capacitance and was surprised that they were good and then set 'em aside.
 




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