The Fine Things are Always Hand Made
A type 55 tube with a wire from one diode plate pin to the grid cap will suffice. This was Scott's recommendation after the Wunderlich tube was no longer available.
I'll be curious to know how it works out.
FYI - A lot of evolution of design during the 15 or so months in production of the Allwave 15.
Although we now have found 5 diagrams, we have also documented some radio examples that straddle more than one of the 5 diagrams. The earlier couple diagrams are Wunderlick tube for the 2nd detector The next 3 diagrams show the 55 tube. The first 55 tube diagrams still shows last IF transformer with a center tapped secondary and the 2 diodes of the 55 tube connected in push pull like the Wunderlick tube. Riders contained only two of the 55 tube diagrams.
If your set is relatively undisturbed, it is pretty safe to stick with what you find in recapping. A Wunderlick tube socket has no tube number embossed and the center button is a dark red. If a later set, the tube socket will have 55 embossed on the socket. Some sets were were returned to the factory and modified to used 55 tube and so the chassis was drilled for the grid cap wire for a 55 tube. One of my AW-15's had what Norman mentioned, a wire tight wrapped to a diode pin to the grid cap.
Before you remove the coil changing wheel to get at capacitors and such, turn the band switch pointer to the broadcast band (full counter-clockwise (7 o'clock)) and do not move it until after you remount the coil wheel. The band switch also operates a contact switch in the top side antenna coil - otherwise you are apt to break the contact switch.
FYI - I can supply a good tested Wunderlick tube.
the wunderlich tube in my set is ok, I was just thinking of future proofing,
someone has already been there as regards to the change wheel removal, the bevel gear was disconnected, and the hexagonal shaft was not mating with the four way switch, also the wheel contacts have been sanded, this I have managed to sort out but will need fixing properly when I start to recap the last chassis,
I have also noticed that there have been several cap changes inside the if cans, so the alignment is suspect,
even so with the exception of a bad audio connection on the main chassis, its a little tappy, the set plays well,
although the tuning meter cant make its mind up what it's supposed to be doing,
it's a real shame what has happened to this radio in the past but I think that it's not too late and can be put right
I have seen more than one base diagram for the Wunderlich tube. That aspect of it is rather confusing. In fact I am wondering if there were other pin-outs of the Wunderlich tube produced. Here seems to be the most common base diagram that I have found:
That base diagram is correct for the most common types of Wunderlich tube and its substitutes. There was also a 5-pin version with a grid cap. I have yet to identify a product employing the five pin version.
OK, thanks. I am working on a cleaned up schematic for the AW-15 with the Wunderlich tube. It is going to take some time to clean up the schematic as it is difficult to read. I may have to ask a few questions here to verify parts values where they are difficult to read.
Here is the latest version of the All Wave 15 equipped with a Wunderlich tube April 10, 1934 schematic. I corrected the mistake regarding the supposed coupling capacitor between the plate of some tubes and the secondary coil of transformers. I removed the capacitance first mentioned and used an asterisk with a note at lower left. A few other minor corrections were made to make the schematic cleaner and easier to understand.
I am surprised to see the significant differences from version to version over time. This early model has the greatest differences compared to the later versions. Some of the capacitor values may be different from what is shown in this schematic, and if anyone finds other values for particular capacitors, we need to document them for posterity.
FYI - There are 5 Scott model Fifteen diagrams that I know of reflecting the evolution of this model. Two for the Wunderlick. The first with a 55 tube appears to use the same center tapped secondary of the final I F transformer with the 55's diodes connected to each end of the secondary. The last 2 diagrams just straped the diodes together off one end of the final IF secondary. But there were a variety of other evolutionary changes as the two red antenna posts for the short wave antenna were eliminated, the double volume pot was simplified, a 2nd outboard static switch appears briefly, etc.
And there are examples in hands of collectors that straddle diagrams.
I will be working on my allwave over the next few weeks, I have printed off your schematic, I intend to make any further modifications and alterations as I go, I think that I will have to find some 56 tubes as I have odd plate voltages on the push pull output stage, one plate is at 270v, the other is about 350v, the readings move with the tubes, I think the one with the higher voltage may be the problem, possible low emission, still waiting for the tube tester to find out which one, also I'm only about halfway with stuffing the original caps, there is still a long way to go.