Some points to consider...

Tubes Asylum

Questions about tubes and gear that glows. FAQ

In Reply to: Tube testing posted by Chubby on August 21, 2001 at 07:24:41:

Hi Chubby,
having three AVOs does not exactly sound like newbie business to me - how does one have to read this?
Anyway, the most accurate of the three instruments tends to be the VCM163.
However, some points are to be considered to make the measurements accurate and comparable.
The Meters - the VCM163 especially - need to be calibrated for your mains voltage. A variation of 0.5 % can have already quite some influence on the measured result.
The AVOs have jumpers to set the mains voltage within 5..10Vs, and then switches to to a fine adjustment. I anticipate you have the manuals, and you follow the procedure.
Another issue is that naturally the readings will only be similar, if the operating point is - I assume bona fide that you test at the same operating point on all three testers.
As well, it is imperative to measure the heater voltage even on a calibrated instrument with the valve under test inserted and heated up for at least one minute - with high heater currents, AVOs sometimes have a considerable drop, and you have to readjust the setting to a value within about 2 % of the nominal value. Use a good true RMS AC voltmeter for it.
Other problem factors may be calibration (how to do you can see in the manuals) and potential bad quality mains supply - the sine wave has to be clean, or the AVOs stray all over the place - remember that they work on self-rectification of the valves. Wrong crest factor means measurement is off...
Best regards,
---mb---
=======
PS: I own a VCM163 and a Mk 4 as well - and they are reliable and produce similar results if used with above-outlined points in mind.
---

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

Follow Ups Full Thread

Topic - Tube testing - Chubby 07:24:41 08/21/01 (12)

Some points to consider... - mb-de 08/22/0102:05:30 08/22/01 (1)

Re: Some points to consider... - chubby 05:17:12 08/22/01 (0)

Re: Tube testing - Gary Kaufman 15:14:01 08/21/01 (0)

If your a newbie.... - mrfixit 12:02:39 08/21/01 (0)

Are your tester calibrated? - Ehien 09:59:39 08/21/01 (0)

Re: Tube testing - kentaja@yahoo.com 09:53:44 08/21/01 (1)

Good sound advice. nt - John PA 10:42:51 08/21/01 (0)

Re: Tube testing - 7N7 08:45:19 08/21/01 (0)

Ebay is scary - Snert 08:28:42 08/21/01 (0)

Re: Tube testing - PÃ¤r 07:27:34 08/21/01 (2)

So that's how they get. . - John PA 08:09:32 08/21/01 (1)

Re: So that's how they get. . - PÃ¤r 23:42:02 08/21/01 (0)

Follow Ups

Some points to consider... - mb-de 08/22/0102:05:30 08/22/01 (1)

Re: Some points to consider... - chubby 05:17:12 08/22/01 (0)

You can not post to an archived thread.