Modified Allwave 23 questions

[Troy Taylor]

Hello-

I just posted some questions about the Allwave 12 I bought last weekend and wanted to ask some questions about a second Scott radio I was offered, but turned down because I have some reservations about its degree of authenticity (it has obviously been modified), and whether or not it would be possible to restore it to it's original configuration.

The second radio is an Allwave 23 and I was all set to purchase it too, but then I took a look at the back of the cabinet and noticed the cover panel was attached with phillips-head sheet-rock screws.  I removed the screws and saw a large mystery box of components and modern wiring, and a terminal strip of wires going everywhere stuck in the bottom of the cabinet.  Some of the wires lead to a large MAGNAVOX speaker that had been shoved in there.  Obviously someone has removed the correct speaker and replaced it with this albatross substitute, and then created some sort of Frankenstein contraption to work around the electrical differences between the factory speaker and this substitute.  I do not have any pictures of this conglomeration, but it is definitely not original factory work, or the work of someone that shares my belief of the necessity of maintaining originality when working on vintage items.

Although it might be functional, or made to be functional, as-is, I am only willing to buy this radio if I discover it is possible to 'unmolest' it and return it to the correct configuration and components it would have had when built.

At the very least it will need a replacement speaker of whatever variety is correct for this radio.  (However, I do not know what kind of speaker this would be.)  Probably everyone wants these speakers for something, so I have little confidence in finding one, but if it is possible to do so, I will reconsider purchasing this radio if I can be sure it is restorable.  I would like to restore this radio correctly, but I have little interest in one that has been butchered in this manner if proper restoration is not possible.

Thank you and best regards-

Troy Taylor

[Y2K Bruce]

I have a nice reconed AW23 speaker Troy and I are discussing for his AW23.

How can I test the speaker to verify it does not have open circuits before I ship it to him? I am not very electrically minded but I think I can run tests on the amp plug pins ?

[Norman S Braithwaite]

If you have a known good speaker, compare readings between the two.

Norman 

[David C. Poland]

Bruce - Also, refer to the electrical diagram. Continuity checks are a good indicator, and noting the resistance readings are in range is even better. 

- plug the short cable into the left 5 pin socket (facing the rear of the speaker) which is the socket to use when no tweeters are used, so that the speaker's big power resistor is in the speaker circuit.

- look at the prong side of the speaker cable's 7 pin plug. There are 2 large pins and 5 smaller pins.  Pin numbering start and end with the two big pins - one is pin 1 and the other is pin 7. Count  CLOCKWISE from a big pin. Refer to the AW-23 diagram. Consider the following resistance values as "ball park".

- the two large pins #1 and #7 are for the field coil. Resistance between them should measure about 925 ohms. 

- pins 2, 3 and 4 connect to the output transformer, pin #2 is the center tap.  Resistance from pin #2 to either of #3 or #4 should be about 50 ohms according to Scott Service Notes. So be about  about 100 ohms from pin 3 to 4. Ball park is good enough.

-  Pin #7, #6 and #5 connect to the speaker power resistor. The power resistor is energized  from the large pin #7. Pin 5 is speaker ground. Pin #7 to pin #6 should be about 3700 ohms. Pin #6 to #5 should be about 1300 ohms.

*

If all these resistances check out as oK, then plug the speaker into an AW-23 for a couple minutes to see how the speaker sounds at moderate volume. Sound should be clear and lack bass without a sound board.  If so, you have confirmed the voice coil and the secondary of the output transformer are both ok.

Hope this helps. - Dave                                                                                                                                                                                                                                

[Troy Taylor]

Hello-

I was very fortunate to purchase the correct speaker for my AW23 radio and it arrived this past week.  It is in great condition and was very carefully and conscientiously packed.  But a completely unpredictable mishap occurred in shipping and I am now looking for advice on the best way to repair the minor damage.  There is a potted transformer in the pedestal of the speaker, which is contained in a metal 'can' made of extraordinarily flimsy sheet metal.  The mounting tabs on this 'can' snapped off in transit and allowed the transformer to rattle around such that it broke some wires off.

Using a sharp chisel I was able to carefully excavate enough of the potting tar to find the ends of the broken wires such that I will be able to reattach new wires to them.  But I do not know where they are supposed to connect.  I have taken some pictures of everything.  For lack of a better reference method, I have added a couple of pieces of tape and arbitrarily assigned letters A-F for the wires internal to the transformer, and #1-4 for what appear to be the corresponding lugs in the speaker itself.  I have assigned #5 to a lug off to the side that has a remnant of broken wire protruding from it. However, I do not know if this is related to the wires broken in shipping, or if it is a remnant leftover bit from previous work done on this speaker.

Based on remaining bits of insulation, I believe that wire D attaches to lug #3.  Lug #1 has no evidence of anything broken from it.  Lug #2 has a black wire bit still attached.  Lug #4 also has a bit of wire protruding, but there is no insulation remaining; I cannot tell if this is a broken wire, or an over-long bit not snipped off from previous wiring work.  And lastly, there is a bit of protruding wire left sticking out from the lug where "BY+K" has been scratched into the paint.  I do not know where this is supposed to go either; it may be a remnant from where the original wire was replaced by the later plastic-insulated wire spliced into that connection from transformer wire A in my numbering scheme.

I am really excited to reunite this speaker with my radio and hope that someone can provide an internal wiring diagram for the speaker and/or be able to determine how to reattach the broken wires correctly, using my letter/number scheme.

Any advice/recommendations are greatly appreciated!  I thank everyone for sharing their knowledge with me as I work to get this radio returned to factory original configuration.

Best regards-

Troy

[Troy Taylor]

Hello-

I was very fortunate to be able to purchase a correct speaker for my AW23 and it arrived this past week.  Despite extremely conscientious and thorough packaging it experienced a minor, and completely unforeseeable, mishap in shipping.  The transformer in the pedestal of the speaker is housed in a metal 'can', made of extraordinarily flimsy sheet metal.  The mounting tabs formed into the 'can' broke off in transit, which allowed the transformer to move around in the pedestal just enough to yank and break several wires off flush with the transformer 'can'.

Using a sharp chisel I was able to remove enough of the potting tar to expose the ends of all the broken wires, and I am confident that they can be easily mended with some soldering and new wire.  But I do not know where they are supposed to be attached.  For lack of a better method of reference, I have put a couple of pieces of tape inside to label all the wires.  Letters A-F have been arbitrarily assigned to the six wires protruding from the transformer 'can'.  Numbers 1-4 have been assigned to the lugs attached to the speaker bracket itself.  Additionally, #5 has been assigned to a lug with a piece of broken wire sticking out.

Here is what I can determine:  Lug #1 shows no evidence of anything broken off.  Lug #2 has a wire sticking out with a piece of black insulation remaining.  Lug #3, with white insulated broken wire, appears to match broken wire D in the transformer.  Lug #4 has a piece of wire protruding with no insulation at all.  I do not know if this is broken off, or if this is an over-long bit not clipped off after previous work.  Lug #5 has a piece of more modern plastic/rubber insulated wire protruding that does not match any broken wire I can find, so I do not know what to think of this.  Additionally visible in the pictures is a piece of black fabric insulated wire protruding from the lug near the letters "BY+K" scratched into the paint on the left side of the photo.  This is also connected to transformer wire A, but again, I do not know if the short remnant is leftover from prior work, or if it is supposed to attach somewhere.

If anyone knows how all of this should be properly reconnected, I look forward to getting this speaker repaired!  Thank you for any advice and information.  I really appreciate how much I have already learned from this forum.

Best regards-

Troy Taylor

[David C. Poland]

Maybe this will help, until more specific info is posted.

The output transformer is a push-pull step down transformer with both a center tapped primary and secondary.

The primary will have higher resistance - so find the high resistance winding, and identify which is the center tap.  Suggest you adhere to the insulation colors as shown on the Riders speaker diagram.

The secondary will have the lower resistance winding, also with center tap.

FYI - Scott changed the speakers about January 1938 - from 38 ohm voice coil impedance (about  30 ohms on a meter) to 19 ohms (about 15 ohms on a meter). the speaker terminal boards also changed.  You need to determine which speaker you purchased. (either speaker will be fine for your AW-23)

Next study Riders Volume 14, to the Scott Hi-Fidelity section page 27 to study the speaker terminal board and compare to your speaker. The terminal board with the wire and spade lug is the early version 38 ohm speaker. Disregard the extra speaker information, concentrate on the upper left speaker terminal board illustration which has the short wire and spade lug being the EARLY version with 38 ohm voice coil.  If your speaker terminal board is different, then you have the speaker with 19 ohm voice coil. 

To complicate things, the Riders amp and speaker diagram is the later version diagram with the 19 ohm speaker.

Hope this gets you started. I am in no position to pull my speakers to take measurements of output transformer resistances for you.  And  have no  shelf speakers to access either.  Good luck.

[Troy Taylor]

Thank you David-

I actually have the complete Rider's set of troubleshooting volumes, sold to me by the same guy that I bought the Scott radios from.  The AW23 is not shown in the index I was referring to, so I assumed that this model was not included.  Thank you for referring me to the relevant pages in VOL XIV!  Last night I looked through the schematics shown and I believe that I will now have no difficulty in repairing the broken wires in my speaker.  There are enough wires not broken, and just enough bits of remaining color coding on those that are broken, that I believe I can sort out which is which without much trouble at all.

I also really like the photographs of the top and bottom of the chassis with all the components identified by part number, cross referenced to the parts list. I think this should make finding and replacing all the necessary caps considerably less difficult than I was envisioning.

Thank you very much and best regards!

Troy

[David C. Poland]

Riders published some master indexes. The 1947 index covers all of  volume 1 through vol 15. It also covers separate huge book called the Radiotron edition - a "catch up" complication of volume 1 to 3 for those businesses who were  not early subscribers.  I bought a reprint 1947 index some years ago, but don't know if it is available now. Try a search.

Scott info for all 1930's model production years through the post war 800B are in volume 14 and some more in vol 15 - but there are notable omissions as Scott models evolved during a production run as, being a custom set builder, he seemed to chase performance improvements.

Each volume is in alphabetic order by manufacturer. However, a manufacturer's models in a particular volume models are not necessarily in order by date or by model number, hence the value of the master index. The Riders Volumes tend to be in chronological order, mostly sort of. Sometimes a manufacturer was really slow to supply tech info to Riders and early info may not have been supplied for a few years, or maybe never.

A complication, the sections of info were sent to a subscriber (service shop) from time to time  to insert the latest batch into the proper Riders book volume. If lazy or careless, the updates may not have been properly inserted. I had one volume with a half inch of update was just inserted at the back of the binder instead of filed properly by page number within manufacturer. And there are instances, where the brand name on the radio is different the manufacturer.  Worth checking the front and back for mis filed material.

[Troy Taylor]

Hello- I finally got some time to start working on the shipping damage to my AW23 speaker and I believe I have sorted out all of the wiring and have everything connected properly again.  This involved making some assumptions, based on the diagram in VOL XIV of Riders on pages 14-17,18 (a fold-out double page), and what was left of the wiring after things rattled loose in shipping.  It became apparent that this speaker has had some wiring work done to it in the past, based on the fact that nearly every terminal/lug in it had stray bits of extra wire dangling from them.  Some wires also had tape wrapped around them that did not appear original.  Before doing anything else, I went through every lug, removed all those extra bits of wire (some had 2 or 3 extra pieces hanging off), and made new, clean solder joints for all the wiring.

All the following questions and wire designations refer to the attached pictures.

The broken wires all corresponded to terminals marked P1, B+, and P2 shown in the schematic.  I had arbitrarily identified these wires as letters D E and F, since absolutely no trace of any of the original colors shown on the diagram remained.  Measuring the resistance between the different wires resulted in the following:

F to E measured 31.7 ohms

E to D measured 36 ohms

D to F measured 68 ohms

Therefore I concluded that wire "E" was the center tap and thus should be a RED wire connected to B+ terminal.

Because the schematic shows an extra loop of wire sketched in between B+ and P2, I concluded that wire "D" corresponded to the higher resistance side of the tap, and should be a GREEN wire connected to P2.

The lower resistance side of the tap is wire "F", which I connected via a BROWN wire to P1. 

Does this seem like a reasonable interpretation of which wire is which and how they should be connected?

Next I went through all the continuity and resistance checks on the 7 pin plug indicated by Mr. Poland.  I got exactly the same readings as specified except:

Pins 2-3 = 32 ohms

Pins 2-4 = 36 ohms

Pins 3-4 = 68 ohms

This is lower than the 50/50/100 (is it close enough to "ballpark"?), but does seem to indicate that I got the connections correct.  I do wonder if there is a potential polarity problem on either side of the center tap though, and how to be sure I did not mix up P1 and P2 connections.

I do not see the early spade lug/wire on the terminal board, so I believe this is a later 19 ohm speaker.  A photo is attached of the terminal board to confirm.

Now the next question is for the wires on the other side of the transformer that were not damaged at all in shipping.  The schematic shows 19 and 38 ohms between the wires.  Are these supposed to be the measured resistance values, or is this a reference to which voice-coil resistance those are supposed to be connected to?  I measured a total of 2.6 ohms across them, split between approx 1.1 ohm and 1.8 ohms.  My Fluke meter is not ideally suited for very low resistance measurements like this, so I realize the math doesn't work out exactly.  Since the speaker worked perfectly before shipping, I assume that these very low resistance values are actually OK.

I want to get the speaker wired up correctly and the damaged wires mended before I start to work on the radio itself, so any advice will be much appreciated. Thank you all and best regards-

Troy

[Troy Taylor]

Hello-

I have started to work on re-capping the receiver chassis in this AW23 and have found that someone else already replaced all the paper caps in the chassis.  However, the schematic shows nearly all of the caps to be .1uf and all of the 'new' caps (not sure what vintage they are, but newer than 1936) are either .047uf or .068uf.  For example: every capacitor in the 4 IF stages is now .047uf, as are the caps in the RFAVC 6B7 tube circuit and the 6A7 converter circuit.

I believe it is best to replace all these again with the correct .1uf value components, but wanted to ask first if there is some possibility that these reduced values are indicative of a Scott design change not shown on the schematic I have.  Or if this is just an example of someone using incorrect components and not worrying about maintaining original values.  Aside from the apparently incorrect values, the work seems to have been competently done.

Any advice about whether or not to replace all these caps with .1uf as shown on the schematic would be much appreciated. Thank you and best regards-

Troy

[Norman S Braithwaite]

Early AW-23 chassis had 0.1-mfd Potter capacitors and later versions had 0.05-mfd OEM (probably provided by Sprague) capacitors.  Any value of 0.047 or more is acceptable.

[David C. Poland]

Also, there is a Scott service bulletin to Scott reps recommending the original 400 volt .1 MFD caps throughout the receiver be replaced with 600 volt .05 caps if the radio is brought in for service.  Later production AW-23 used the .05 mfd 600 volt caps. 

Modern 630 volt .047's  are good replacements. But - there are few caps with other values which are NOT  to be changed to .05's - specifically, the .01 on the fidelity control, the two .05's on the bass control switch.