The Fine Things are Always Hand Made
The Wunderlich tube was a 100% American invention. The possibility of a modern substitute has been discussed on this forum. The discussion can be accessed at the link below.
I figured the tube being called "Wunderlich" that it was a German invention - such are assumptions. Thanks for the link! I see that I had contributed to the thread previously. My memory on things sometimes fails me.
I like the 3A5 method as a substitute. I am thinking of trying this in an experimental set. Thanks again.
The Wunderlich tube was devised by Norman E. Wunderlich of Chicago, a consulting engineer. I picked up an 8 page tech description by Mr Wunderlich some years ago at a radio auction.
Arcturus Tube Co co-sponsored his development of the tube and associated circuit, designed as a high quality 2nd detector, as a perfected grid detector and for circuit designed to control sensitivity - thus automatic volume control. It is a full wave detector with some amplification as well. The tube has two of co-planar grids - interwound an equal distance from the cathode. Wired to the secondary of the final IF coil, one grid to one end of the secondary and the other grid to the other end and the secondary is center tapped for a bias source to control sensitivity. The arrangement is similar to a full wave B+rectifier circuit.
E H Scott was a pioneer user of this tube. I understand Crosley used it for a model too. Scott used the 6 pin 2.5 volt version. There is a 5 pin version with grid cap and a 6 volt automobile version but I know of no radios using those versions.