6Н2П Tubes

I recently bought 4 6Н2П tubes on eBay from Lithuania. They were made in Russia during Soviet times and were 1984 NOS stock costing about $2 each. They are a direct equivalent to the 12AX7 but have 6.3 volt filaments on pins 4 and 5 so not directly replaceable without rewiring the supply. I couldn't wait to try them out in my PH6 and although their gain and general performance was up to spec they suffer terribly from microphony, so bad that even turning the volume pot could be heard as a squeaking sound on the speakers. No good whatsoever in a high gain circuit but probably fine in a line-level amp.

Here is a physical comparison.

Left to right: JJ, Electroharmonix and the Russian 6Н2П.
The JJ and the 6Н2П have similar plate heights which are shorter than the Electroharmonix but the JJ has the mica plate end pieces touching the glass.

Thanks for the info!

@ goddlediddles
These are recommended to be used with small input signals. ( Very high amplification factor: 100 ). try the Russian 6N2P-EV variant. I use them in a modified DAC and the plain 6N2P is not as clean sounding as 6N2P-EV according to my ears. (I have only tried the Russian made ones ). Just be aware some sellers are shipping used tubes, or mixing used with unused ones. I learned the hard way.
As a side note, to vent my frustration I step on them to crushed them but they wouldn't, I took a hammer and after the first few blows still they would not brake, it took me a while to brake them.
OH COME ON !!!!!!!!!!! I love recycling !!!!!