Dating rca vacuum tubes
A separate filament transformer was used on the switching box to simultaneously heat all six comparison tube filaments without overheating the amplifier's power transformer.
The purpose of this comparison is simply to provide guitar players with a frame of reference to help in finding the best current production 12AX7 for their needs.
Tube tests as new with phono/V1 grade noise levels.
The 1965 Amperex 12AX7 / ECC83 tubes in this precisely matched pair have gray plates and halo getters (I65 series). This rare 1950s Arcturus 12AX7 tube has short black plates with copper grid posts and a D getter.
From the frequency plot it could be seen that there are three extrema at about 50 Hz, 400 Hz and 4,000 Hz.
These three frequencies were then used to quickly measure the low, mid and high frequency voltage gain on the same number of samples for each tube in our comparison.
They are labeled for Hammond organs and matching Heerlen, Holland factory codes are etched in the glass. This 1960s Amperex ECC83 / 12AX7 tube was made in Holland and labeled for organ, hi-fi audio, or medical companies. The white print on the glass has the Arcturus logo.