KT-88, KT-77, Russian 6SN7 makes "pops". Should I touch their pin with an iron?

[tubularfluxus]

KT-88, KT-77, Russian 6SN7 makes "pops". Should I touch their pin with an iron?

I once read on a forum that Russian 6sn7 Melz (hole plate) tubes are prone to produce "pops" and other distortions, but could be fixed by touching their pins with a warm iron.

I do have few of those Russian 6sn7 and in fact most of them produce pops every now and then.

I also have a KT88 (Genelex UK), new never used, which does the same (produces pops) and when tested swings the needle of the tester around the "?" or "Bad".

And I have one or two KT77 (Genelex UK), also new, that do the same "popping".

Has anyone had experiences fixing tubes by touching their pins with a warm iron? If so, can you tell me more? Should I touch their pins by having the tube staying straight (rather then upside down) to let the solder inside the pins reflow?

Thanks!

 

[bulgin]

Those tubes are expensive and I wouldn't 'touch' their pins with a hot soldering iron.

bulgin

 

[JonSnell Electronic]

It is very unusual to have a poor connection within the soldered part of the plug. Have you checked the Octal sockets? That is more likely to be the issue due to people constantly changing the valves, the sockets wear out.

 

[tubularfluxus]

Usually this "pops" problem happens only with these specific tubes.
With the KT77, if I replace them with a different pair of el34, the problem disappear and the amp is quiet. Even if I knock on the tubes, no noise comes.

Back with the kt77, after a minute or two of use, it starts to pop, and if I knock on the amp itself or any tube (kt77, 12ax7 and 5r4gys rectifier) it makes more scratchy noises...

 

[kevinkr]

I've had a number of NOS tubes with bad solder joints in the pins which I fixed by reflowing the solder in the pin, sometimes adding a bit more. Do this with great care.

At least one of these tubes was a Genalex (UK) KT88 which went on to live a long life.(And got sold as a good used tube for far more than I paid for it new)

 

[tubularfluxus]

Glad to know the trick worked on your tubes! How did you make the soldered reflow? Heating each pin for few seconds holding the tube straight? I guess if I hold the tube upside down the soldered may flow backward and short circuit some pins?

 

[JonSnell Electronic]

If you must do this, use plenty of flux and no solder as there should be plenty there already. Time is critical, be quick with a hot iron to avoid damage to the valve base. As soon as you see the solder melt with the new flux, that is it, done.

 

[AllenB]

IIRC the metal used within the pins is carefully formulated to have the same thermal expansion coefficient as the glass to prevent breakage. I wouldn't want to contaminate this deep in the pins.

 

[kevinkr]

I heat them upside down, and usually apply some flux and a very small amount of solder to assure a good thermal connection between the iron and the pin. They're quite heat tolerant IMLE, and you have to get it hot enough to reflow the solder. Have never had any problem with shorts or damaged tube (valve) bases.

 

[merlin el mago]

Kevin what temperature & time did you used?