Bigger steel body, early prototype! Those tubes were started to produce in year 1939 like EF13 and EF14 also.
Bottom code dr = September 1939!
Excellent sound and build quality!!
Tested on RoeTest V10 (the best modern tube tester!)--see attached picture for measured data
PRICE IS FOR ONE TUBE!!
I will pack and secure tubes good.
Replacement black box!
Feel free to contact me.
AT