Wunderlich tube in AW15

[Christopher Tubbs]

I have a AW15 which, according to Mr. King, was made early October 1934.  I am assuming that this set has to Wunderlich tube in it.  I'm trying to figure out here that tube is placed on the chassis.  The attached photo has some of the tube shields with numbers on top for ease of the tube location...are any of the numbered shields the spot for the Wunderlich tube...or is it some place else.

I have a piece of Scott literature that has and order form for a matched set of tubes for the AW15 ( all 15 tubes for $8.00!) and it notes a type 1, type 2 and type 3 of which the type one and type 2 have the Wunderlich tube in them, but the type 3 has a 55 tube now in place of the Wunderlich tube (with all the other tubes still being the same from type 1 and 2)  My thought is that with the Oct. 1934 build date, it's maybe a type 1 or type 2. 

Thanks!

[Kent King]

The 2nd detector is location #7. The AW15 is a very difficult set because Scott was <constantly> upgrading them in production. And to make matters worse, if you sent it in for any service - they often updated it with some of the more crucial changes. I have (not so jokingly) said that every AW15 is unique. I've got (I believe) 7 schematics and of course Scott had his 3 Types, the best way to identify a <possible> schematic is to get the entire tube lineup and then find a diagram that matches, or is close. 

I may be able to help with info, but a complete tube lineup from the chassis is the best way to start.

Kent

[David C. Poland]

The tube sockets have the tube number embossed on the center button. Except, for a Wunderlich socket, the button is dark red, same color as the tube base of the cobalt blue glass Arcturus Wunderlich tube. (3rd tube back on the left side).

That being said, some Wunderlich tube sets were updated to use the 55 tube, which involved a couple circuit changes and addition of a grid cap wire. Also some early AW-15 sets repaired by the factory may have had the set updated to use the 2A7 as 1st detector. Therefore, noting the actual tube sockets embossed numbers may help you match your example to an early Wunderlich set diagram.

FYI - The Wunderlich tube was  designed as a full wave 2nd detector tube and audio amplifier and to provided negative variable voltage for AVC (automatic gain control). Scott first used it beginning December 1932 - mid production of the 12 tube Allwave Deluxe (AW-12) and continuing for the 1934 model FIFTEEN (aka AW-15) for the first few month until about Fall 1934. The Wunderlich tube had 2 interwound control grids. The last IF transformer secondary is center tapped. The two grids were wired to the ends of the secondary winding. The center tap provided the negative AVC voltage. Being full wave, the wiring is a bit like a full wave high voltage rectifier circuit.

The Wunderlich tube was not widely adopted,  used briefly for only a couple models by few other radio manufacturers. The tube became rare, so, difficult to replace. Some Scott's were converted to use the later, and more popular, 55 tube with it's two diodes and triode construction. Our website includes the suggested wiring changes for the 55 tube conversion.

[David C. Poland]

This 55 tube was found in the Wunderlich socket of my AW-15 LEDO console, an unrestored AW-15 early production Wunderlich model.

IMG_0637.jpeg

This 55 tube has an external wire connecting diode #1 (pin 4)  to the grid cap, the triode grid. The wire is wrapped around tube pin 4 and soldered, as is the other end to the grid cap. Would seem to interfere with the full wave (push-pull) detection circuit, but maybe not?

I have heard of doing this. Lacking a suitable, restored and unaltered Wunderlich model, I have not tried it to see if this tube modification actually works. I had to downsize my collection before I could get to this restoration, and my remaining AW-15 has the factory modification to use the 55 tube.

[Kent King]

Dave P reminded me I had a modified type 55 tube sent by Scott in 1946 to replace a Wunderlich. Went and found it and tested it in an Allwave Deluxe tonight. You can't hear any difference-replace the Wunderlich with the special 55 and it plays the same with no circuit mods. Scott also published a full circuit update for the AW15 and Deluxe I placed that PDF file in the Archive in the AW15 folder.

Kent

[Kent King]

Sorry - its in the Deluxe folder!

Kent King said:

Dave P reminded me I had a modified type 55 tube sent by Scott in 1946 to replace a Wunderlich. Went and found it and tested it in an Allwave Deluxe tonight. You can't hear any difference-replace the Wunderlich with the special 55 and it plays the same with no circuit mods. Scott also published a full circuit update for the AW15 and Deluxe I placed that PDF file in the Archive in the AW15 folder.

Kent

[Christopher Tubbs]

Thank you guys for the info!  Very interesting!

I had forgotten about the tube sockets being numbered for the tube, so thank you to Mr. Poland for reminding me on that.  So I then carefully removed the tubes the other night to to see wat was on the sockets.  My AW15, chassis L-319 has 6-56, 4-58, 1-2A7, 1-55, 2-2A3 and 1-5Z3 tubes making it a type 3 according to Scott.  The spot for the 55 tube is un-numbered and maroon in color.  Since the tube configuration matches with the the type 3, I'm assuming it's original and Scott just used the un-numbered sockets because they were still on hand and worked..."waste not- want not" I thinking.

Type 1: 6-56, 5-58, 1 Wunderlich, 2-2A3 and 1-5Z3 
Type 2: 6-56, 4-58, 1 Wunderlich, 1-57, 2-2A3 and 1-5Z3

With the progression of the different tube combinations from type 1 to type 2 to type 3, what is going on from a a technical or design stand point?  Is the type 3 say better than the type 1 arrangement?  It looks like the type 3 has a 2A7 replacing the 57 and a 55 replacing the Wunderlich from the type 2 design

What brand of tubes would have been used by the factory when it was originally built and first sent out?

[Kent King]

Coil%20Wheel%20Updates.pdf

OK - many things to respond to. I did attach these two items, they may be of interest. The 2A7/55 was the "final" AW15 design by Scott. The 2A7 is far superior as an RF stage than the 58. And a 55 is far easier to find than a Wunderlich. To your last question, Scott was using primarily Arcturus tubes in 1934 - but his transition to Sylvania wasn't far off. Either would be a great choice for an AW15.

Kent

[David C. Poland]

Take patience now to tube up an AW-15 receiver with a set of cobalt blue glass Arcturus tubes. I did that with an AW-12 Deluxe AVC Wunderlich tube set. The blue glass looks impressive with the chrome, even tho hidden inside the tube covers. Over the years, I did find a couple Scotts that still had a few blue Artcturus remaining. There was a period when Arcturus changed to clear glass and printed the word "BLUE" on the glass near the top - found a couple in a Scott. Ahhh - what fun such trivia.