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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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21st Aug 2017, 1:56 pm | #1 |
Hexode
Join Date: Feb 2014
Location: Southampton, Hampshire, UK.
Posts: 419
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Resistors gone low
Hi,
The following resistors are in series with the mains as surge limiters to the rectifier in a Kolster Brands FB10. I have read these sets are notorious for component changes so was not surprised to find what looked like two 330 Ohms resistors in parallel. The trader sheet (969) shows a 150 Ohm in parallel with a 470 Ohm giving 113 as the listed value for V5 surge limiter. However I measured 83 Ohms from what looked like two 330 Ohm resistors in parallel, they could be two 220 Ohms but they definatly look more orange than red. Removing them showed one at 123 Ohm with the other at 257 Ohms. This value is constant when measured with a DVM and when derived from the current flowing with 10 Volts across the resistors. Interesting phenomenon, any comments. Photo attached. |
21st Aug 2017, 2:14 pm | #2 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
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Re: Resistors gone low
Over run low value resistors tend to go lower in value, on the other hand high value ones say approx 100k and above tend to go high with age.
Used to get this in various locations, one was cathode bias resistors in frame or audio output stages. Once they start to go low it's a vicious circle, valve draws more current, resistor heats up more and goes lower in value. Quite a standard event. Frank Last edited by Nuvistor; 21st Aug 2017 at 2:40 pm. Reason: Spelling |
21st Aug 2017, 2:16 pm | #3 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Resistors gone low
Second that.
Lawrence. |
21st Aug 2017, 7:58 pm | #4 |
Hexode
Join Date: Feb 2014
Location: Southampton, Hampshire, UK.
Posts: 419
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Re: Resistors gone low
Thanks for the comments not really noticed it before -a new modern componant required I think.
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21st Aug 2017, 8:29 pm | #5 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: Resistors gone low
That's interesting. Every vintage resistor I've ever seen seems to drift up. Particularly carbon comp ones. Never noticed if there was a difference between high and low value ones.
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21st Aug 2017, 8:55 pm | #6 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
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Re: Resistors gone low
The low ones seem to go low when overrun, which in many domestic TV, radios of the 50's and 60's was common, or perhaps near their wattage limit.
Some would go O/C after going very low, the heat would crack them in two. Frank |
21st Aug 2017, 9:03 pm | #7 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: Resistors gone low
Will keep eyes peeled for that one. Might explain a few things I have had in older 1960s Tektronix kit as well that left me scratching head.
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22nd Aug 2017, 12:37 am | #8 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
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Re: Resistors gone low
The colour code seems to indicate a non-standard 230 ohms. That would be quite close to the mentioned 470 and 150 ohms in parallel.
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22nd Aug 2017, 7:22 am | #9 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,991
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Re: Resistors gone low
Careful what type of resistor you use. Carbon comp ones are very good at handling surge currents, whereas modern resistors tend to be metal film and not handle surges well at all (ie burn out).
An alternative, although non-authentic, would be to use wirewound. |
22nd Aug 2017, 7:40 am | #10 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
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Re: Resistors gone low
A WW resistor as a surge limiter in that location in the KB is what I would use, not authentic but probably more reliable.
Frank |
22nd Aug 2017, 8:02 am | #11 | |
Octode
Join Date: Jan 2004
Location: Southport, Merseyside, UK.
Posts: 1,156
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Re: Resistors gone low
Quote:
John |
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22nd Aug 2017, 8:10 am | #12 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
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Re: Resistors gone low
Probably whatever they could source in enough quantities.
Frank |
22nd Aug 2017, 8:55 am | #13 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,967
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Re: Resistors gone low
We used to find high value carbon resistors around line output stages and boost lines on TV's could go low as well as high. General rule of thumb was resistors between 100K and 1M could go low and high whilst resistors greater than 1M would generally go high.
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Simon BVWS member |
28th Aug 2017, 1:18 am | #14 | |
Dekatron
Join Date: Dec 2007
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Re: Resistors gone low
Quote:
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