GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Melquiades Amplifier
In the Thread: Is it the time to change those tubes?

Post Subject: The built-in tube testers.Posted by Romy the Cat on: 8/1/2013

The concept of self-testing boot cycle is nice one but it for sure could not be done during the amp booting. Some tubes do need to warm up and reach the cruse temperature in order to be tested, some do not. Some tunes (like 6C33C) in fact is best to test during the warming up: by looking how the parameters change during the first 10 mine of tube operation a lot might be said about the tube. Fromm a certain perspective any tube amp is a tube tester and all it take is to slightly reformat the tube operation and bring the data in an interpretable format. The interpretable format is kind of tricky as it would depend from the type of the tube.

Generally looking into a mutual resistance of the tubes we can have some idea about the tube life. I feel that change in mutual resistance in a way a good indicator of tube life but we can’t presume that it has to be some kind of fix number as all tube testers do. It is not the absolute number what is important but rather the change of the number as the tube ages. A rate of decrease of tube gain, the “mu” with decreasing filament voltage of plate voltage is good indication for some tube. The testing of cathode emission is a good indication for other tube. Some tubes (like 6C33C) might be very easy to be tested by looking how bias changed since the tube was broken in. so, in my view there is no universal way to test all tubes but any given amp for sure can test own tubes in the best way to itself.

I think it is a good idea to make any amp that more or less expensive to have a self-testing capability. However, this direction has own “issue”. The amplifiers make sell the replacement tubes and they have huge mark up on those tubes. Letting them to moderate the tube testing is not advisable in my view. It is like my spa dealer goes over himself by advocating do not use ozonizers in hot tabs. The little dirty secret is if his clients use ozone for water sterilization then they buy much less spa chemicals and spa replacement parts from the dealer. Me, being skeptical and believing that any industry person would screw anything that permitted to be crewed, I personally would not trust build in amp tube tester. At least I would need to recalibrate then to my own sense of what it right and wrong. I know, it is a bit paranoiac but it is what it is. If you even buy from a “trusted souse” the matched tubes that ended up to be grossly and even laughably mismatched then you know what I mean.

Rgs, the Cat

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