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Re: [Amps] VTVM Diodes

To: amps@contesting.com
Subject: Re: [Amps] VTVM Diodes
From: "Will Matney" <craxd1@verizon.net>
Reply-to: craxd1@verizon.net
Date: Tue, 16 May 2006 12:33:16 -0400
List-post: <mailto:amps@contesting.com>
David,

The tube type differences could be the gain, or voltages, I'm not sure. The 
probes could possibly work, but those are the ones that used an acorn tube in 
the tip aren't they? Here's the biggest problem. If you change the tube(s), the 
meter will about sure be out of calibration. What happenes is that as the meter 
was used from when it was new, the tubes gradually got weaker while the meter 
was sent out once a year for calibration. Each time it was re-calibrated, it 
was to the weaker tube signals. When you put a new tube in that is 100%, it 
throws off the calibration. Solid state meters don't do this to that extent. 
The yearly calibration for solid state I don't think is needed. Maybe every 
three years, and that's if they're really used a lot. However, if a solid state 
is repaired, it needs to be checked for calibration then unless the part was 
out of the same batch as the original. Even then, there's a possibility it 
could be off because of the gain difference. The tube meters
  though really need the calibration over shorter spans over the tubes gain 
dropping over use. How much a new tube could throw it off, I'm not sure.

What you could do is measure some standards if you have them, and write down 
the measured values. Really they don't have to be standards, just save the 
original parts you used to test back for the last test. Compare these 
measurements to the ones you get after you replace the tube, and adjust for 
them.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 5/15/06 at 4:36 PM David C. Hallam wrote:

>I am trying to find an AC probe for my HP-410C.  I have a probe from a USM
>116 VTVM.  The 410C uses an EA53 diode in the probe and the 116 uses an
>EA52.  From what I have found on the internet, these two tubes seem to be
>similar, base connection, heater voltage, frequency range, etc.  Does any
>one know if I could use the probe from the USM 116 on the 410C?
>
>David
>KC2JD
>
>
>
>
>
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