[Boatanchors] newbie question

[Glen Zook]

I disagree!  I have seen numerous occasions where a mutual conductance tube tester showed a particular tube to be bad but, in the particular circuit, the equipment met, or exceeded, minimum specifications.  I have also seen occasions where a tube tester showed a tube to be good but, in the particular circuit, the tube would just not function.

Remember, a tube tester only checks the tube at a certain DC voltages and there is absolutely no test at any r.f. frequency.  Also, in many circuits, the need for the highest gain, etc., is not needed and, therefore, the "bad" tube works fine in that particular circuit.

A good example of a tube testing good but not functioning in the circuit is the 6C4 used in the tunable oscillator in the various Hammarlund receivers.  Many 6C4 tubes check good and yet will not function, especially on the higher frequency ranges.

In the "goode olde dayes", 01A tubes that did not have sufficient gain were branded as 00A tubes and used in circuits like detectors.  

Just because a particular tube does not have the most gain, that doesn't mean that the tube is useless.  Everything depends on the actual application and many circuits just do not require the highest gain, etc.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: "WA5CAB at cs.com" <WA5CAB at cs.com>
To: boatanchors at mailman.qth.net 
Sent: Sunday, June 30, 2013 10:03 PM
Subject: Re: [Boatanchors] newbie question
 

This is an often repeated statement, implying that if the tube tester says 
the tube is bad but it still works in the set, the tester is wrong.  A tube 
can still work in a circuit but be bad.  Meaning in most cases that it's 
gain is lower or much lower than the minimum acceptable for the type.  So if 
the tube tester result is ignored, the repair person never figures out what's 
wrong with the radio.  Moral of this story is that if you have a good tube 
tester and it says a tube is bad, believe it.  

On a somewhat related subject, several of us have run enough tests over the 
years to confirm that the I-177 and TV-7 setting chart settings for the 1R5 
are wrong.