I am very confused. So, the Amperex 6922 is not good? From the AI FAQ, it says:
"Only "mil-spec, low-noise" 6922, 6DJ8, 7308 or European E88CC tubes are recommended for use in Modulus preamplifiers.
Previous production Modulus M2, M3, M3a and L1 preamplifiers used Russian 6922 tubes. While quality and sonic performance of these tubes were excellent for several years it is unfortunate that current-production from the Sovtec/Reflector factory does not have the same sonic identity and a high percentage prematurely fail.
Current production Modulus M3a and L2 Preamplifiers use a Russian Military Type 6922 with "Grey Plates" and have excellent sonics and reliability.
Similar tubes which have different technical specs should not be used.
7DJ8 tubes require higher filament voltage and performance is marginal.
6NIP tubes should not be substituted as they require additional filament current and their use will compromise performance."
So, the 7D8J and 6N1P conflict with Joe's comment. And Joe said 6922 is not suitable? ... So, the remaining choice are:
6h23n, 6DJ8, 7308, E288CC ?