TUBE STRAINTH VS. PERFORMANCE

[Stellasstillarat]

Will a transmitting tube put out it's rated power even if it doesn't test 100% or better? If the tubes checks out at 70% good will it put out only 70% of it's rated power and one that checks to be 90% good put out 90% of it's power? Or once a tube checks out to be good should it theareticly put out it's rated power? Thanks

 

[Atlasta]

The rated quality of a tube is only one factor in whether or not the thing is any good. If it's gassy, has a short or has grid emissions it may still light up and test well but not be worth keeping.

Example: Recently I saw a little ripple on the scope while running my Phantom. I pulled and tested all the tubes and they all came up better than 95%. One tube however showed a short and had grid emissions. You would never know it just by looking at it. That tube was replaced and the ripple went away.

Tube testers, unless you have a high-end Hickok or some such are at best a rough estimate.

What I have found is making sure that the contacts are clean and the tube is well-seated- not to mention ventilation- is more important than how strong it is. That, and don't key down and talk on them for an hour if you're on AM- that's a surefire way to send tubes, especially sweep tubes- into meltdown.

 

[Captain Kilowatt]

I agree about tube testers being basically a GO-NO GO test. Tubes generally will perform at full output for most of their life and then s-l-o-w-l-y drop in output which is generally the first sign of them approaching end of life.

 

[Stellasstillarat]

Once again you have answerd a question that any layman (myself) can understand. This information will no doubt save me hundreds of dollars if not, help me decide whether or not to retube an amp or just sell it/keep it for parts. At the ridiculous prices amplifier tubes are selling for the latter would be the smartest choice. My 300a 's output is still very close if not exactly what Palomar's manual rated it at. I'm assuming the tube are strong. With 21/2 in I see 400 out and over 500 on ssb with 12 watts. For now it's a keeper. Thanks Capin.

I agree about tube testers being basically a GO-NO GO test. Tubes generally will perform at full output for most of their life and then s-l-o-w-l-y drop in output which is generally the first sign of them approaching end of life.

 

[Stellasstillarat]

Thanks atlasta. I did some research that expanded on you answers. If I do need tubes I now know who to buy them from. There's a few tube sellers that check tubes for the exact issues that can make a tube that shows good on a go / no go tester basically worthless. if I didn't ask the question and you didn't respond I may have purchased tubes that are worse than the ones I may be replscing. Your information was informative and eye opening at the same time. I've learned that go/no go tube testers are them selves a no go when there, the only criteria for which a tube seller base's his "tube tested 90% good at". Good stuff. Thanks again

The rated quality of a tube is only one factor in whether or not the thing is any good. If it's gassy, has a short or has grid emissions it may still light up and test well but not be worth keeping.

Example: Recently I saw a little ripple on the scope while running my Phantom. I pulled and tested all the tubes and they all came up better than 95%. One tube however showed a short and had grid emissions. You would never know it just by looking at it. That tube was replaced and the ripple went away.

Tube testers, unless you have a high-end Hickok or some such are at best a rough estimate.

What I have found is making sure that the contacts are clean and the tube is well-seated- not to mention ventilation- is more important than how strong it is. That, and don't key down and talk on them for an hour if you're on AM- that's a surefire way to send tubes, especially sweep tubes- into meltdown.