12 tube chassis Identification.

[Bob Cofer]

I started on my newly acquired 12 tube, in Napier cabinet. There is one tube I can’t Identify. The mark has worn off the tube, and it the only socket on the tuning chassis that does not have the tube identifier stamped in the socket. The tuner chassis has three 56’s, one 57, four 58’s, and the tube I can’t identify. The power supply uses an 80 and two 45’s. The tube in question is a six pin tube. Can anyone tell me what the mystery tube is, and how to find schematics for the correct chassis? Thanks.

[Kent King]

The mystery tube is very likely the Wunderlich detector. In the archive area, go to Set Folders, Allwave Deluxe and you want the 1933 Allwave Deluxe Rider schematic - should match your set pretty closely. Scott's were custom built, so there might be very minor differences, but that is the best one you can use.

If you have questions - just ask, everyone here is pretty helpful!

Kent

[Bob Cofer]

Thank you so much Kent.  That is exactly what it is.  It has “wunderlich 2.5V” stamped on the base.  This is a new one on me, I never heard of it. I easily found the schematic from your instructions.  Thanks again.

[David C. Poland]

Bob - a tip off is the center button on that mystery socket is dark red, much like the dark red of the base of the blue glass Arcturus Wunderlich tube -  a push-pull 2nd detector.

Scott used the 6 pin 2.5 volt version, beginning December 1932 as an upgrade to the 12 tube Deluxe Allwave and continuing into the early months of the succeeding Allwave Fifteen model introduced Spring 1934. Only a couple other radios ever used it. There is a 6 volt version, that remains a curiosity.

This tube was designed not only as a 2nd detector, but also to provide AVC (automatic volume control) as well as an audio amplifier. It has 2 grids, which are co-planer - coiled around each other, equidistant from tube cathode. Looking at the circuit diagram, note the last IF coil is center tapped and one end of the IF secondary is connected to one of those grids, and the other end to the other tube grid. AVC voltage arises from the center tap of the last IF secondary coil..

The tube has a low stress electrical environment and is considered long lived, but like other globe tubes the interior is not well supported, so dropping it may shock and bend the interior thus ruining the tube. 

The 2.5 volt Wunderlich tube became unavailable and some sets were modified to use the 55 tube. But in recent years a number of used and NIB Wunderlich tubes have turned up. If you need one, I have a couple available, good tested.

 

[Bob Cofer]

Thanks for all the great information David.  I sent you a friend request and message regarding the detector.