[HAM] Testing 6550s

[David Anderson]

Someone wrote:

>> Is there a tester reading for old Tung-Sols 6550's? I know someone  
>> who
>> has a pair in an old PA amp...Or is it just as long as the tester  
>> reads
>> "good?"

Testing output tubes can be tricky because I've seen them test good  
when they don't sound good.

Testing is a good way to make sure that it's safe to plug the tubes  
into your amp--no serious failures.

But I've seen both Tung Sol 6550s and Mullard EL34s that *tested*  
good, but sounded muddy and muffled in circuit. They seem to lose  
their ability to reproduce higher frequencies.

There are also several different types of tube testers from the  
simple emission type to the better type that measures  
transconductance in a roundabout way to the serious Hickok testers  
that give you more accurate readings.

I won't buy used output tubes anymore for this reason. It's too much  
of a crap-shoot even if they "test" good.

David