Broken plastic guide on tubes - how to tell which way the tube fits in socket?


I have a few tubes (and also a set of 6SN7>6F8G tube converters) where the plastic "guide" with the notch that tells you how the tube fits in the socket is broken off. Any way to tell which way the tube or adapter is supposed to fit in the socket without experimenting and frying the tube?
slaw3
Post removed 
Not sure how I would know which direction to install it however.
If you have a DMM, you can identify the filament pins by using continuity test. In the case of 6SL7, the filament pins are 7 and 8.

http://www.tube-fullmusic.com/Fullmusic%20Tube/6SL7/6SL7_01.jpg 

https://lh3.googleusercontent.com/proxy/zkwJL9ulSQRrAamWEPO2Ows4F-Fy7fMd-iu_9Pu09fbrsjlkCcnBAPfgijm7...