In the last century I bought a few thousand tubes and tested them with the computerized curve tracer Sofia by Audiomatica. The tubes I purchased were mostly direct heated triodes ( DHT ) and high transconductance noval. Over time I have kept only the most linear tubes and matched them. In the coming weeks a part of my collection will be on sale (among these DHTs such as UX201A, CX301A, 171A, 112A, CV1660, 3A/110A, AC/P4, 801A, 10Y, 801 RCA ceramic base, RE604 TFK globe, RE084, RE134, D3A Siemens, etc )
If you need information on the interpretation of the curves or enlargements of specific areas, just ask.
It should be noted that Sofia's software makes an error when measuring direct heated tubes.The cathode reference point is lifted up by half of the heater voltage; so, for example, when the filament is fed at 4 volts, all curves are actually measured at 2 volts less than nominal. The curve you see at -40 volts is actually at -42 volts. The higher the voltage of the filament, the greater the difference (especially with the family of 10Y/VT25/VT62/801A etc with a 7.5 volt filament the error is 3.75 volts) You can read about it on the dedicated page in Sofia by Audiomatica on the Jac music website.
Auction for one matched pair of Arcturus 101A blue globe used ( my numbers no 01 and no 02) Full emission, same construction.
You see the curves of each triode and the third image with the curves overlapped
For any infos and for combined shipping, please ask. For shipping outside Europe, please ask for better prices