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Hum and other problems with "NOS" power tubes?

post #1 of 8
Thread Starter 

I bought some Tung-Sol 5998s (8 of them) from a dealer. They were sold as NOS, but I guess I've been ripped off.

 

Some are top getters, others bottom getters. Several of them have a hum, and one makes a cracking sound. My question is this: if a tube really is NOS, will it hum? Make cracking sounds? I don't have a tube tester, but am trying to find someone who does in the Copenhagen area, so I can get the tubes tested.

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post #2 of 8
Quote:
Originally Posted by rich.no View Post

I bought some Tung-Sol 5998s (8 of them) from a dealer. They were sold as NOS, but I guess I've been ripped off.

 

Some are top getters, others bottom getters. Several of them have a hum, and one makes a cracking sound. My question is this: if a tube really is NOS, will it hum? Make cracking sounds? I don't have a tube tester, but am trying to find someone who does in the Copenhagen area, so I can get the tubes tested.



I've never bought a NOS tube that was anything but 100% working right out of the box.  Usually they will come in a 5-pack and I just select 2 of the 5 at random.

 

That being said, I clean all tube pins with Deoxit before I use any tube that is new or that I've had in storage for a while.  In the past I have had situations where certain tubes had a hum or an electrical buzz, and in the majority of cases using contact cleaner on the pins solved the issue.

post #3 of 8

Also try to clean the pins with a small brass wire blush before using the Deoxit. Oxidation is the tubes number one enemy here. Even a spec of it will cause hum or popping as I have noticed first hand.

 

And yes I have bought NOS tubes before and they all had a hum or some hissing, but cleaning the pins always solved it for me.

post #4 of 8
Thread Starter 

Thanks for your replies! I sent a mail to the dealer after reading them, he assured me the tubes were tested good on his AVO tester, but that if the hum persisted after pin cleaning I could return them for a refund :-)

 

I can't seem to find Deoxit anywhere in Denmark, but will try with some isopropanol and cotton swabs first. If that doesn't help I'll try to find some Deoxit or its Danish equivalent, which seems to be "Kontakt 60".

post #5 of 8

I would use the brass bristle brush on the pins as well.

post #6 of 8

What if there's oxidation on the socket? Is there any way to clean that?

post #7 of 8
Quote:
Originally Posted by Armaegis View Post

What if there's oxidation on the socket? Is there any way to clean that?



Don't dry off the tube pins all the way after spraying them with deoxidizing cleaner, and then insert them like that.

 

The stuff isn't dangerous at all to electronics.  I know people who do vintage receiver repair and spray the crap out of the inside of units all the time with the stuff.


Edited by GotNoRice - 1/24/11 at 4:00pm
post #8 of 8
Thread Starter 

Thanks for your help guys. Cleaning the pins with alcohol and cotton swabs solved the problem :-) I tried finding a metal bristle brush, but my hardware store didn't have one.

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