BAD TUBE(can you tell by looking?)

[Carcass29]

Just wanted to know if you can look at a tube and tell if it's bad? I have a quad set of 6L6's from my recently departed 5150 and want to try them in my JSX....I know one of them has kicked so any idea's? thanks

 

[dreamcatcher]

Well, sometimes you can tell by comparing the glows, or if there is physically something loose in one of them. Or like if one smokes or something

 

[Carcass29]

Well, sometimes you can tell by comparing the glows, or if there is physically something loose in one of them.

Physically, they are perfect...I shake them and listen for noises and nothing...I'm afraid to put them in my current amp to check for the "glowing" because I don't want to blow anything....any other ideas?

 

[006]

Find a friend with a tube amp that uses 6l6's. Tell him you want him to try the power tube in question in his amp to see the "gain difference". Then you can see the glow. If there is nothing really wrong, then ask him if he hears the difference. If he says "not really, sounds the same" tell him he's a noob and that he needs to get his ears cleaned out.

~006

 

[Andy Sneap]

tap them with a screwdriver, if one makes alot of noise through the amp, it's usually a duffa, becareful though, just a gentle tap on the top of the glass

 

[Death Is Certain]

tap them with a screwdriver, if one makes alot of noise through the amp, it's usually a duffa, becareful though, just a gentle tap on the top of the glass

The handle of a tooth brush works as well.

 

[Carcass29]

Thanks for the advice everyone...i'll give the tapping a go.

 

[JeffTD]

Screwdriver, chopstick, toothbrush... it all works. The tube should make some noise, just not a ton.


Also, that test works to detect microphonic (squealing) preamp tubes, as well .

 

[Carcass29]

ok...I've been tapping the tubes, each of them has a higher to low pitch. I tapped them outside of the amp(holding them in hand) and tapped them in the amp with the power on...am I doing this right? So far I turned the power on and played through them...sounds very 5150ish and I also noticed my stock 5150 tubes were not 6L6Gc's but 6L6wxt's. They all lit up in dull blue color...all except one, that may be the faulty one but so far no disturbances in quality of the sound.

 

[Carcass29]

Here's a clip with the 6L6's.....
http://www.acidplanet.com/components/embedfile.asp?PID=719203&embed=1&t=1674

 

[~BURNY~]

Power on is the way to go. You should be able to hear microphonic tubes making a ringing noise through the cab. But no noise doesn't mean that tubes are in perfect working order. Also, power tubes should be matched pairs and biased for best performance and longevity.

 

[kaomao]

tap them with a screwdriver, if one makes alot of noise through the amp, it's usually a duffa, becareful though, just a gentle tap on the top of the glass

Just preamps tube become microphonic tappin them with a screwdriver.
When powertubes are dying they lack of body (lowend) generally.

Maurizio