[Test-Equipment] What are "cathode jacks" on a tube tester?

[Brian Clarke]

The plural of 'jack' is 'jacks'. The possessive of 'jack' is 'jack's'.
What you have done we call the butcher's apostrophe, alluding to the
possibility that butchers don't know much about English grammar and
punctuation.

Normally, in email correspondence, we remove the unnecessary tails.

On Sunday, 30 June 2019 12:00 PM, Pat said:

The cathode jack's are one of the two sets of banana jack's that have
jumpers at the top of the tester. One possible use is to insert a resistor
to simulate using cathode bias.  FWIW, I've never found a need for this
feature.

Pat
wa4tuk