Audio Asylum Thread Printer

Get a view of an entire thread on one page

FAQ / News / Events

Tubes Asylum

The sad about testers are they dont tell much of a story.

66.188.56.2

[ Follow Ups ] [ Post Followup ] [ Thread: Display All Email ] [ Tubes Asylum ]

MIchael Samra

In Reply to: Minimum value of each tube tester posted by b9ronaldo on March 17, 2006 at 15:36:10:

Ronaldo
The first tubes you mention which are preamp tubes will not get much data from even the best testers for all paramaters of the tube.
How many times have we put 12ax7s in a tube tester and have them read 25% of new and yet perform perfect in a preamp..By the same token I have seen high testing mullards or RCA 12ax7s only to be microphonic as hell when put in a circuit.
If your buying high priced preamp tubes used,always go to a reputible seller..I get a higher price when I sell my 12ax7 telefunkens becuase my testing not includes emissions and leakage and shorts and mutual conductance,but I also have a signal generator hooked up to both sides of the tube with a set of high impedance headphones and while Im injecting a 5khz signal into the tube for about 40 minutes straight while periodically tapping the tube and listening for microphonics..if I hear any then the tube gets rejected.This is the only way to test real functionality.. I have it set up so I can do this on my heath tt-1 and my sencore mu 140.

Follow Ups:

25% & perform well........... - Jimmy 03:04:08 03/18/06 (0)
I sold a pair of Mullard ECC82 on ebay. These were not like new tubes & usually below spec of what I normally sell. However, they tested close to new gm specs & were not GE late 1960s tubes vplus held up well on the reduced filament 'life' test. The buyer applies their tests via a tube tester and states these are well used tubes. Their tube tester is NOT a good test, just a weak approximation of remaining tube life. To get away from an ebay negative, I had to refund the full amount. I am sure they are enjoying the tubes, however the A$$ was sent to my blocked bidders list.
Re: The sad about testers are they dont tell much of a story. - b9ronaldo 02:14:56 03/18/06 (1)
I know, but at least good testing result "normally" represent good tubes, I buy 200 items last 2 years, when seller say test NOS only 5% disappoint me while 50% tubes fail when ebay seller state "my tester broke" or "I didn't have tester".....
Ofcause, a reputible seller like deserve higher bid, but when we found something too rare or item I look too long, it sometimes deserve some risk.
- Re: The sad about testers are they dont tell much of a story. - Mark Bos 15:17:54 03/18/06 (0)
  There's a seller who says, "I usually test tubes from my stash just before I use them, so these aren't tested, but they should be good."

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

You can not post to an archived thread.