Wunderlich substitute

[mike hadley]

Has anyone tried to substitute the wunderlich as fitted to the all wave sets,
I was thinking along the lines of an old tube base turned into an adaptor with a 3a5 that has its anodes connected together and heaters in series, this would plug in with no mods to the chassis,
I will probably be shot down in flames for suggesting this but if it works there is a whole lot more 3a5 / dcc90 tubes than wunderlich's out there

[Joseph W Strickland]

David;

Thanks for those differences mentioned. I am not surprised after seeing the number of differences already documented in official E. H. Scott schematics and parts lists. The technology was rapidly advancing during this period and Mr. Scott was incorporating new ideas as production continued. It has been mentioned here before that some customers returned their sets for repair and their sets had as many modifications as practical incorporated into them before they were returned to their owners.

Mike;

It appears that the output tubes may have suffered from leaky coupling capacitors that caused one to conduct much harder than normal and resulted in low emission in one. Since the readings move with the tubes the fault does not appear to involve the output transformer. A new set of output tubes will likely solve the issue. I do not know if anyone offers matched pair tubes of the type used in the AW-15.

Joe

[David C. Poland]

Joe,  Nice job on your cleaned up April 1934 diagram.

More on set variations:

I kept the 5-17-1934 diagram on which I made notes for a Wunderlick set I had for awhile -  Ser# #H-416.

Contrary to the April 1934 version you started with and the May 17 1934 factory diagram, this set used 57's (rather than 58's) or both the RF and the mixer. Otherwise had the 2 additional antenna posts for shortwave, the toggle switch for antenna selection, the center tapped 4th IF secondary for the Wunderlick in push-pull, the single pot volume control of the May diagram and 5 position sensitivity control.  A person can grow weary of trying to develop diagrams to reflect set variations that straddle the known factory diagrams.

[Joseph W Strickland]

David;

Thanks for the compliment on the schematic redraw. It would be interesting to see what the differences are between the type 57 and 58 tubes. The type 57 may have had slightly better RF gain or different internal capacitances that provided some sort of benefit in performance. On the other hand I have seen manufacturers switch tube types due to monetary or availability considerations.

As to getting weary, yes it takes a lot of time and effort and rechecking to get the diagrams right. I just spotted a few parts values on the revised drawing that need to be changed from the original hand written values to typed values, so there will be one more iteration of the schematic. This one has taken me several days of effort. One thing that helps is that once a drawing of a tube type's internal parts or a capacitor or resistor representation has been done it can be copied and pasted repeatedly to create the schematic and saves considerable time. This particular schematic was so faint and blurry I felt it best to redraw it using more modern representations of the tubes to aid in understanding the schematic.

Joe

[Joseph W Strickland]

David;

I prepared a second version of the All Wave 15 equipped with the Wunderlich tube based on your comments and the schematic that I did for the first version. Would you please take a look at it and see if you can identify the resistors that were added in the sensitivity control circuitry? The schematic in the database is not legible in that area, so this is an attempt to create a schematic that can be read easily. One other question I have about this version, is the sensitivity control part of a band switch or separate? It looks like the input transformer has added taps for each band to optimize the sensitivity for each band as well as providing gain control optimizing.

[Joseph W Strickland]

I looked at the specifications for the type 57 and type 58 tubes. There is little difference, some slight differences in input and output capacitance. The data on the type 57 says it is similar to a type 6J7 metal tube and the type 58 says it is similar to a type 6K7. Of course the filament voltages are different with the type 57 and 58 having 2.5V filaments and the 6J7 and 6K7 having 6.3V filaments. The type 57 seems to be more suited to mixer/detector circuits while the type 58 seems better suited to RF/IF gain stages controlled by AGC/AVC according to the information from RCA tube manuals.

Joe

[Joseph W Strickland]

Mike;

Did you get a chance yet to check your audio output tubes to see if the one with high voltage has low emission? I have one tube tester that covers the older tube types such as the 2A3, 56, 58, 80 etc. and another one that covers all the more recent miniature types plus Octal and Loctal variants. I remember seeing adapter units that would plug into older tube testers to allow testing of the newer types. I think most shops moved to newer tube testers instead of the adapter units. In our cases, we are not on a time schedule, so we can afford the time to use more than one tube tester or an adapter plug-in to cover all the types.

Keep us posted.

Joe

[David C. Poland]

Joe - I did not make extensive notes  on that radio other than the use of the 2 type 57 tubes. and that it was pretty much the May 1934 diagram.

Do you have the May 1934 factory diagram?

[Joseph W Strickland]

David;

I have a May 1934 diagram, but it is such poor quality that I cannot read many of the parts values. I can see certain parts that disapppeared and some others that were added, but very few values that are clear enough to read. It appears that a switch section was added to the antenna input which moved to select taps on the input transformer and select different trimmer resistors for the RF gain according to the band selected. I can not make out those values. I believe I see some other values around the 1st detector and in the IFs that changed but cannot be certain due to poor copy.

Joe

[David C. Poland]

Joe - email me your address - I 'll mail you some 11 x 17 things that are much clearer.

 dave -  [e-mail]

[Joseph W Strickland]

Dave;

I just sent you an e-mail. Mine is [e-mail].

Thanks for your help!

Joe

[David Dodgen]

Hi,

New to discussions here.  I am having difficult time locating a Wunderlich tube for my AW 15.  I liked the idea of a substitution by using another tube such as the 3A5.  Since Im not well versed in this technology, I hope that someone has tried it and could suggest a tube and adaption to plug into the Wunderlich location.

David

[David C. Poland]

Dave, - I suspect no tube will work as well as a Wunderlick in your AW-15 set.

The Wunderlich has a pair of co-plainer grids, connected to the ends of a last IF coil center tapped secondary in a push-pull type way. And the tube also functions as an audio amp of the detected audio signal by that tube.

The "strap pin to the 55 grid cap" approach is a stop gap solution to get the radio playing.

I have an AW-15 that was modified (by factory?) to use the 55 tube with minor wiring change and adding a grid cap wire from below. I think reception suffers compared to a later version AW-15 designed for the 55 tube which I also have. I have an unrestored early Wunderlick AW-15 which I look forward to being able to compare. The Wunderlich tube is in a low stress position in the radio, but in a globe type glass envelope lacking internal of a soldered type envelope is subject to damage if dropped.

FYI - I can supply a good used Wunderlich tube - tested for emissions in my early Supreme tester and also tried in a Wunderlick 12 Deluxe I have. If interested - [e-mail]