Many books were written about tubes, here only a few details. In the last years, many types have been reproduced, forget about the hype of NOS tubes, a new tube is cheap and good. With JJ / Tesla tubes I almost never had a failure or problems with noise and they are electrically highly robust. Also EH or Sovtek are not bad.

Octal tubes

Pictured different octal tubes, unfortunately no pre amp tube with it. Interesting for example is the 6SL7 as V1 for harp, which lies roughly between 12AT7 and 5751st.

Here you see a rectifier 5Y3GT, a silicon rectifier with damping resistor GZ34, an old RCA 6V6, a Sovtec 5881/6L6, a Brown Base KT66 and KT66 by JJ.

Tube at 250V (OT) Heating Current Power Loss
6V6 4,5k 0,5 A 14W
6L6GC 2k 0,9 A 30W
KT66 2,5k 1,3 A 25W
EL84 5,2k 0,75 A 12W

Interesting is the determination of the output impedance to select the correct pins of the output transformer. Therefore you square the anode voltage in volts and divide by the power loss. In the example with the 6V6 that would be 250²/14 and you get 4464, means 4,5K.

Noval tubes

The noval tubes in the top row: a collection of double triodes, ascending by gain. TT12AU7, EH12AY7, TT12AT7, JJ5751, JJ12AX7 and a JJ ECC803, an AX with longer sheets for more foundation.

In the bottom row, a rectifier JJ EZ81, a pre amp pentode EF 86 and a power amp pentode EL84.

Tube Gain factor
12AX7 ECC83 7025 100
-- -- 5751 70
12AT7 ECC81 6201 60
12AY7 -- 6072 40
12AU7 ECC82 5963 20

Pin assignment