Retainer per valvole EL84

Installed in an old hybrid italian SE amp (GEM/Galanti Mercury G10 - 1972 / BC209C preamp + EL84 power tube).
In those amps, Tubes are upside down, with no HF protection or retaining system, to avoid microphonics. So this point is partially corrected, tube is now secured and vibrating is limited with this part.

Springs are very firm and cannot easily be turned (one star left) ; I got max tension because of non-adapted tube socket, but it's OK.
Just take care anyway : do not broke the glass when installing...