[Amps] THE SKINNY ON MY AL-82

[Carl]

You havent lived until you find a 47K that became 1-2 Meg which is quite 
common in many old receivers and sourced at only 200-250VDC as screen 
droppers.

Over 50+ years of building and servicing tube gear Ive only found a handful 
that went down in resistance.

I have a conservative 10K of NOS carbon resistors and about half again in 
used condition going back to the late 20's

Carl
KM1H




----- Original Message ----- 
From: "Hardy Landskov" <n7rt at cox.net>
To: "Colin Lamb" <k7fm at teleport.com>; "Bill Turner" <dezrat at outlook.com>; 
"Amps group" <amps at contesting.com>
Sent: Sunday, December 21, 2014 5:19 PM
Subject: Re: [Amps] THE SKINNY ON MY AL-82


> It's been my experience that the 2 watt ones are the worst. I measured 1 
> meg resistors that have drifted up to 2.5 megs.
> So, think your high voltage is low and your power supply is going south? 
> Measure the resistors first that feed the voltmeter.
> 73 N7RT
>
> ----- Original Message ----- 
> From: "Colin Lamb" <k7fm at teleport.com>
> To: "Bill Turner" <dezrat at outlook.com>; "Amps group" <amps at contesting.com>
> Sent: Sunday, December 21, 2014 2:46 PM
> Subject: Re: [Amps] THE SKINNY ON MY AL-82
>
>
>> Regarding carbon comp resistors:
>>
>> "Not necessarily. Carbon comp resistors can drift both up and down in
>> value.  I've been replacing them all my life, trust me on this one.
>> They are essentially unpredictable."
>>
>> Many years ago, I tested some 2 watt 250 ohm carbon comp resistors for 
>> stability.  I heated them up to dissipate 2 watts in open air.  After a 
>> relatively short period of time (I do not recall the time, but it was a 
>> number of minutes), I measured the resistance and it had increased.  I 
>> thought I could go through a number of cycles and have it stabilize. 
>> But, every time I ran it through a cycle, the resistance changed.  At 
>> first, it went up in resistance.  But, soon it started going down.  It 
>> never was stable.  And, each resistor was different.
>>
>> I have numerous old Allen-Bradley 1/2 watt resistors on the shelf and 
>> some are stable, while some are not.
>>
>> Colin  K7FM
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>
>
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