How does a lower current for the heater at the same voltage affect GM?

Tubes Asylum

Questions about tubes and gear that glows. FAQ

I have many 1193/CV6/6S5S tubes. They all have a 300mA heater draw and measure from 2700 to 3300 for mutual conductance with a minim acceptable of 1900. The plate current varies on the tube and is higher than the D1148 Hytron but that is not the question.
I have over 100 E 1148 Hytron tubes that were made in 1944 under contact to the US government for the military. They have a heater draw of 200mA. The spec sheet shows they would measure the same as a 7193 but they do not.
They sound excellent and work fine but I am trying to figure out why they by design or because of a lower heater current, measure typically 2000 to 2300 in Mutual conductance/GM and a lower plate current. Gain seems to be the same but for some reason it seems that Hytron varied from the specs in a lower measuring tube. I would put the minimum at 1300 to 1400 GM vs the 1900 (on a Hickok) as the minimum.
I have two 539C calibrated testers that I can test current draw on and a couple of TV7 calibrated (Dan Nelson)testers and they all match up.
These are all NOS in original military boxes and never used. All the 7193 types use 6.3 volts for the heater.
Any ideas?

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Edits: 10/22/23 10/22/23 10/22/23 10/22/23

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Topic - How does a lower current for the heater at the same voltage affect GM? - John PA 13:08:56 10/22/23 (5)

RE: How does a lower current for the heater at the same voltage affect GM? - Triode_Kingdom 21:42:00 10/22/23 (2)

Yes, the E1148 is a direct replacement for the 1193/CV6 tube. . . - John PA 22:07:30 10/22/23 (1)

RE: Yes, the E1148 is a direct replacement for the 1193/CV6 tube. . . - Triode_Kingdom 05:56:24 10/23/23 (0)

RE: How does a lower current for the heater at the same voltage affect GM? - Chip647 18:31:54 10/22/23 (1)

I understand that but . . - John PA 19:19:55 10/22/23 (0)

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