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

[Thomas Day]

When I re did my early Allwave 23 I used the .1 value caps except for the specific .05 values which were original.

Not sure how much difference it makes, it would probably change the cutoff frequency in the IF strip the most.

The impedance of a .1 VS .05 at 465 Khz might or might not be a concern. It doesn't seem to matter much.

Thom

[Troy Taylor]

Thank you to everyone that responded!  I was working on this radio all day Saturday at the home of a retired tube electronics guru that has been coaching me through the work.  Before receiving any responses to my forum question about the values, he recommended going back to the original .1uf values, which is what I ultimately did in the places where the schematic showed that value.  I did use .05uf where the schematic and/or parts list showed that value.  If a "Potter" cap means the tar-filled bathtub style used in my AW12, then I can say that my AW23 was not built with that kind of capacitor when new.  No original caps were still present when I started working on the chassis, but there is simply no evidence of bathtub type caps having ever been installed or removed.

More questions to follow about a few other discoveries in this chassis, as soon as I can get some good pictures to post with them. 

[Norman S Braithwaite]

The Potter capacitors used in the AW-23 were conventional wax-paper capacitors in orange cardboard cylinders with rolled ends.

Norman

[Troy Taylor]

Hello-

I was able to get some pictures to go along with my new questions.  The first picture shows a capacitor and resistor in series, dangling off the volume control pot.  This is clearly not a factory installation.  The value of the cap is .01uf and the two components in series run from the lug visible on the pot in the photo to another lug on the far side of the pot not really visible in the picture, but located very near the black 'spot' on the outside of the pot at the 5:00 position.  I doubt this is the original volume control pot, but do not know what the original would have looked like.  I do not see a resistor and .01uf capacitor in series like this on the schematic, so I am looking for suggestions on what I need to do to return this to factory configuration.

Related to this question is the terminal strip soldered to the vintage Brown Black Yellow resistors on the right side of the photo.  The two lugs located one to each side of the resistors both clearly had components soldered to them in the past, but they are presently not tied to anything.  Would these lugs have been used for components related to the volume control, prior to it's being modified with the dangling parts?

The second picture shows the underside of the tube socket for the 76 oscillator.  I believe that the two .05uf caps are tying the filament pins to ground, since the remaining pins are all soldered to the switch contacts as shown in the schematic.  But there is nothing I can find on the schematic showing caps tied to the filament pins.  What might be the reason these caps were added?  Would it be better to leave them, or to remove them?

[Norman S Braithwaite]

Leave the 0.05 mfd capacitors attached to the oscillator filament lugs.  Better yet, reinstall them with shorter leads.  They were a production run change to improve oscillator operation.

Norman 

[Troy Taylor]

Hello-

I reinstalled the .05 uf caps with shorter leads, per Norman's advice above, and am slowly progressing with this restoration.

I have started working on the power supply/amplifier chassis for my AW23 and will be ordering new capacitors soon.  Someone has already been in there, probably two different times before based on the variety of different replacement caps installed.  They are all different values than those shown on the schematic; I think someone put in whatever they had.  I will be ordering the values (or whatever is nearest still available) from the parts list, but I have a question about C8 shown in the parts list/schematic.  The value given is .13 uF, but no voltage is listed.  Does anyone have a recommendation about what sort of caps would be best for this application in the circuit?  I cannot tell if these are original or if they have already been replaced.  There are 4 of them in there.

Is it safe to assume that C7 and C9 do not need replacing?  They look like mica/domino style caps to me.

Also, C2 shown in the parts list, a 1/10-1/10 300V cap is one I cannot physically find.  Is it hidden in the transformer case?  The arrow pointing to it in the parts list diagram does not look like a component present in my chassis.  So if it is not hidden, then I am assuming it has been removed.  What am I looking for?  Would it be acceptable to replace it with two discrete .1uf 630V caps?

Any suggestions/advice would be much appreciated.

Thank you and best regards-

Troy

[Troy Taylor]

I disconnected some leads that prevented a clear view of the C8 caps (four in total, on the underside of a phenolic panel) and can see that they have definitely been replaced at some point.  None of them are .13 uF value.  A photo is attached.  Would a parallel combination of 630V caps equaling, or nearly so, a .13 uF value be suitable as replacements?

Also attached is a photo of the area that the 1/10-1/10 300V cap is supposed to be according to the Scott parts list diagram.  I believe that this dual cap is missing.  Am I correct?

Thank you and best regards-
Troy

[Norman S Braithwaite]

The four 0.13-mfd capacitors are part of a whistle filter that sharply attenuates the 10,000 hz audio signal generated by an adjacent station carrier.  This feature was included because the IF bandwidth of the AW-23 accommodated experimental high fidelity stations (Apex stations).  The IF bandwidth can be widened to 32-khz with the "fidelity" control yielding a potential audio signal of 16-khz.  They should be 0.13-mfd +/- a small amount but it is best to select values based on performance of the filter.

The 0.1-mfd capacitors (0.25-mfd in later sets) are "buzz filters".  Please be aware that these are rated for 1300-volts, not 300-volts.  They reduce buzz in the power transformer and help protect the power transformer from impulse voltage spikes.

Norman

[Troy Taylor]

Hello-

I cannot find a .13 uF capacitor but can get the exact value by combining .1 with .03 in parallel, so that is what I will do.  The rating is 630V on these.

C2 is listed in the parts diagram from Scott (Page 14-26 in VOL 14 of Riders) as .1-.1uF, 300V.  This is the one I am wondering about, since it appears to be missing from my chassis.  The line drawing on this page does not clearly show anything that appears to be a capacitor.  From the schematic, it looks like they are "Line-To-Ground" filters, that should be replaced with the modern Y2 style.  This is what I intend to use, as that is what the application looks like in the schematic, unless I am mistaken.

The high voltage .25uF caps are in the parts list as C4, listed at 1250V.  I have found .2 and .05 replacements, rated at 1600V that I will combine in parallel. 

Thank you and best regards-

Troy

[Norman S Braithwaite]

The line filter capacitors were only used on later production sets.  If your set had them there would be two rivet holes on the end of the chassis.  Replace with no more than 0.015 mfd otherwise they will trip GCFIs.

Norman 

[Troy Taylor]

Hello-

My capacitor order arrived and I have gone through the amp/power supply chassis and re-capped everything.  I was not able to sort out the previous work, as it was unclear exactly what the guy had done or why.  The 30 uF caps were replaced with a pair of 47uF and a 22uF, the 2uf was not in the circuit at all, the high-voltage .25uF filter caps were also gone, and there were two 100 uF caps wired in, instead of the single one shown in the schematic.  Also it appeared that some wires were gone as well.  I disconnected/removed the previous work and set about returning the circuit to match the Scott schematic.

Since I never got to see how this chassis was originally configured, I had to create my own layout from scratch.  I hope it is acceptable.  I added terminal strips under the choke mounting screws to provide tie points for the new components.  Any original Scott components not shown were gone before I bought this radio; I removed only more recently added items.  I left the 1966 dated 30uF capacitor cans on the chassis for cosmetics; they are not part of the circuit now at all.

Attached are before/after pictures of everything except the 100uF, which I installed in the location shown on the Scott line drawing from the service information.  I used .2uF + .05uF 1600V caps in parallel to replace the missing .25uF 1250V called out in the schematic.  I used .1 + .03uF 630V caps in parallel to replace the .13 uF caps in the "whistle filter", which had already been replaced with .1 uF as shown in a photo posted earlier.

I also have not installed the .1uF line filter caps because A) I am not sure where to put them yet or if my set even came with them and B) I had already ordered .1uF value before Norman recommended using .015uF instead.

Before I attempt powering this up on the variac, I have a few more questions:

The voltage regulator 'tubes' in the receiver chassis are called out as NE42.  My chassis has a pair of NE32 'tubes' instead.  I know nothing about this kind of tube and they are not listed in any of my RCA manuals.  What is the difference between NE32 and NE42?  I have not been able to find NE42 tubes for sale, so if anyone has a source for replacements, I would appreciate an opportunity to buy the correct ones.

I seem to be missing an internal tube shield as pictured.  I see four places that have a place for one of these, but my set only contains three.  Does anyone have a spare shield like the one shown in the picture that they would be willing to sell?

Lastly, and this is not related to power-up, but more general cleaning, there is black smudging all around the small numbered dial to the right of the printed numbers.  Is this supposed to be there, or is this something that should be cleaned off?  It doesn't look like a pattern, but also appears to be printed on with the same 'ink' as the numbers.

Any advice would be much appreciated.  If anyone sees something I need to change before attempting power up, please speak up.

Thank you and best regards-

Troy

Edmonds, WA

[Troy Taylor]

Additional photos of dial smudging, NE32 regulator 'tube', and the missing style tube shield.