Will an EV-81 tube fit in a Border Patrol DAC?

Sorry for inaccurate description.  I should have listed EZ81 rectifier in title, not

EV-81 tube. Excuse my ignorance. 

I would NOT do it.  The EZ81 draws 1.0 A vs. 0.6 A for the 80.  Could damage DAC

A great reference for tube equivalents is any late model Hickok tube tester owner's manual.   

Thank you for help and pointing me in the right direction for tube equivalents!

Sure.  You always want the pin out the same , most important!  And also important is the filament voltage and heater current.   

Look up a Hickok tube sheet for 12ax7.   You will see there are a number of variants, ECC83,7025, CV4004.   12ax7 and 7025 are US designations , ECC is European , CV is a British variant.   

Here's an example of EZ80 and it's cousins.  If you notice there are certain caveats.  I always check the tube data to make sure what is on a sellers page is correct 

https://www.vivatubes.com/6ca4-ez81-6v4-ez80/#:~:text=The%206V4%20and%20EZ80%20are,can%20handle%20higher%20plate%20voltage.