Tube with microphonics appetite

[catalin gramada]

Hello. I bought a batch of russian 6H9C to use it as equivalent for 6SL7. The tube seems pretty difficult to manage due some issues. First it is very noisy suplied by AC on heaters. Elevation help till a point only in negative side. I supplied heaters by DC and is quite dead. Second is prone to interferences. Ok I solved also screened the tube with a tube shield.
But worst I found the tube is microphonics as hell. The stories not start from begining and tested tubes from diferent batches I found some decent pieces not microfonic at all at first use. Still all becomes microphonics in couple of days.
Hwat the heck ? How a tube can become microphonics after couple hour of use ? I wonder if is a matter of tube issue or the application I did ? I suplied tubes with 350V runing less than 1 mA through . Heaters dc supplied 6.5-6.7v around.
if is a tube issue it is a matter of mechanical internal structure ? How can I do an investigation to resume what is responsable for this microphonics comportment in time please ? Thanks.

[Mick Bailey]

I bought a batch of these NOS tubes all made in 1982 and had similar problems. Perhaps about half were good specimens, though when I bought them they were really cheap - $1 US each, so I wasn't too disappointed. I think the heat cycling loosens the internal structure - when tapped you can hear the mechanical rattle, but some were rattling and microphonic right out of the box.

Did yours come in a box like this?

[catalin gramada]

I bought a batch of these NOS tubes all made in 1982 and had similar problems. Perhaps about half were good specimens, though when I bought them they were really cheap - $1 US each, so I wasn't too disappointed. I think the heat cycling loosens the internal structure - when tapped you can hear the mechanical rattle, but some were rattling and microphonic right out of the box.

Did yours come in a box like this?

Is exactly the same situation in my case. Get it without boxes . The suplier sells it from a big X00pc /box. Still I have tens of pieces from diferent batches from 1963 to 1980. All of it have a stamp certified quality controll. All of it are the same, did not found any diferences in terms of noise or microphonics comportment. The crap is pretty consistent. Comes direct from Russian source and cost as same as yours.

[stokes]

Maybe cheap Russian tubes just suck out loud?

[catalin gramada]

Maybe cheap Russian tubes just suck out loud?

I don't say it sucks. Still are good tube to use if are not rattle in a head in top of a cabinet. And to be honest I like it more than new Tung Sol 6SL7 GT who btw draw 600mA in heaters, at least the 4 pcs recently bought paying a small fortune for it.