tube rolling kit SSh2

Hi there,
Just curious to know what the difference on the 18FX6 and 18FX6A is? One of the pairs I got is a 18FX6/18FX6A pair, hence the interest.


The 'A' designation means that the heater has a specified / controlled warm-up time. That characteristic is useful when several tube heaters are connected in series.

In reality, there likely is no difference - I suspect all 18FX6 tubes were made to accommodate series heater strings, as that was the common application in AC/DC tube radios.