Allwave 15 in Tasman Cabinet Electrical Restoration

[Jon Ketron]

Several months ago I was able to purchase an AW15 housed in a Tasman cabinet.  This beautiful receiver is somewhat special as the tuner chassis is still riveted after all these years.  I picked up this set in Kansas City.  Quite a drive for me, the price was right and worth the effort.  The previous owner was a radio collector.  This AW15 and a poor condition AW23 were all he had left.  A very nice fellow, I asked were he picked up the set.  He stated the receiver had been in his possession for quite some time, purchased from another radio collector back in the 1990's in Wisconsin.

As to the riveted tuner chassis.  There is a cardboard sleeve located on one of the electrolytic cans. Learning from fellow Scott collectors and research, this cardboard sleeve signified a prior E.H. Scott repair, meaning this receiver was brought back to the Scott factory for repairs either during the 1930's or early 1940's.  These tuner chassis were originally riveted shut once they left the laboratory.  E.H. Scott offered a 5 year warranty on all his receivers.  The warranty would become void if someone removed these rivets or tampered with the set.  After this AW15 had it's repairs completed, the laboratory installed new rivets.  The tuner chassis has not been opened since.  A true time capsule.

What makes things even more interesting:  The antenna post set up would indicate this machine to be an early version AW15.  Dave Poland had mentioned the toggle switch on the far side looking at the back of the receiver was a two position tone control of sorts.  In place of the Wunderlich tube resides a #58 tube with grid cap lead.  The socket is not labeled with a number.  The Sensitivity control escutcheon shows 5 positions.  I can only turn the control three positions (will look into this further once chassis is opened).

My consensus would be this receiver either was a transition from early production to late production, or received these modifications once the receiver was brought back into E.H. Scott Laboratories for repairs.  I must note; there is a #450 inscribed on the inside of the power supply.  This too signifies prior E.H. Scott repair.  It is interesting to think about these variables as the AW15 model in general went through so many changes during it's year long production run.  I would greatly appreciate any input you might have on this matter.

I find it interesting that the 2A3 output tubes are of the Arcturus brand, test 90% percent emission with no shorts.  No way these could be original unless this set was not used often or these are replacement tubes.  I should have the results of the power supply shortly.

Jon 

[Jon Ketron]

Thank you both.

The second "Potter" resides near the Wunderlich socket.  This capacitor seems to have been added to the circuit via E.H. Scott.  Value looks to be a .025, would you concur?

Thanks,

Jon

[Kent King]

Here are some coil wheels I just had sitting about...the 3 that are directly opposite are all out of AW23. I have no mark/set label on the one with the non-opposing felt strips. Not a "one-off" apparently. Looking at the odd coili, it is NOT an AW23, probably a 15 or even a 12.

Norman S Braithwaite said:

The felt strips are for cleaning the contacts.  I believe they were included on all AW23 coil wheels.  Your example is the first I have seen where the felt strips are not opposite each other.

Norman

[Jon Ketron]

Kent,

Thanks for including other examples.  Glad to know the felt set up on this AW15 is not a "one-off".  Perhaps E.H. Scott figured they needed to be off set during an AW15 revision?  Correcting to what has been seen on an AW23?  Did the AW12 deluxe or two dial have felt pads?  Important to note Mike's AW15 and the early version AW15 I completed before this one both do not have felt pads present, no pre-drilled holes either.

Jon

[Jon Ketron]

I have taken a closer look at each dogbone resistor.  I find it interesting to have discovered most have the word "Continental" stamped in the center.  There are also resistors present without this logo.  The last AW15 early version restored did not have the word "Continental" stamped on any of it's dog bones.  Was there a change in manufactured parts utilized via the Laboratory between 1934 and 1935?  I am interested to find out why two different variations exist.  I have seen these "Continental" stamped dogbones on an AW23 as well.

Thanks,

Jon

[Thomas Day]

Jon:

Most manufactures, Scott included, went with the least expensive components available that would still provide the quality of performance needed. It also depended on the quantity of parts needed for a given production run.,and supplier availability to deliver on time.

When I was on the service bench for a small manufacturing company, this was often the case when components needed to be replaced in a customer's equipment.

[Kent King]

Jon -

Scott frequently changed suppliers, during the Depression, availability of parts was always a tough issue. Scott changed tube preferences along the way too, early on, he used Arcturus, later sets always include Sylvania tubes. Repairs would only add to the differences in a given set. 

Figuring out specifics as they relate to manufacturing dates, parts used, etc., would be an impossible task 80 years later. In addition to factory mods, you have sets serviced elsewhere too...So, when I do restorations, I just look closely at the set I'm working on, compare to known schematics, and occasionally sketch out a change to see what it looks like. I'm working on a 23 tuner at the moment and documenting the effort...I'll post more here when it is done.

Kent

[Jon Ketron]

Thank you both.  I understand it will be difficult to get answers with regards to parts utilized via E.H. Scott as too many variables exist.  I find it interesting the early version previously worked on had no labeled resistors while this E.H. Scott modified unit does.  As both of you stated, availability of parts could be the cause.  From research, looks to be E.H. Scott had it's highest volume of civilian sales and receiver demand between 1934-1937.  Perhaps "Continental" out of Cleveland Ohio was ready to answer the call when resistors were needed.  I too wonder if Continental was the primary supplier before and started to label their resistors in the mid-1930's as seen on this late modified AW15.  I have also seen these Continental resistors inside of an AW23 model.

Jon

[Jon Ketron]

I need to revisit the 025 mfd cap again.  I have taken a detailed look at both the early and late version schematics.  The late version schematic seems to be matching up to most of the values present within this set.  The added Potter cap that goes in between the plate of the type 55 tube and resistor connecting to the volume control shows 025 mfd on the paper cover.  The schematic shows this value to be .25 mfd.  After consulting with a friend it has been determined a higher MFD value would induce more bass into the circuit but could also cause motor-boating as a side effect.  A lower MFD value would induce less bass into the circuit.  I have a strong feeling to go with a .025 mfd despite the schematic showing .25 mfd.  I am interested in your opinion on the matter as to which cap value should be utilized?

Thanks

Jon

[mike hadley]

Jon;
If you put the value of the volume pot and the coupling cap into an online calculator it gives roll off at roughly 125hz, if you then multiply the cap value by 10 this gives 12.5 hz, maybe a little excessive, I think that 0.025uf is the way to go.
Mike

[David C. Poland]

We do find an occasional occasional misprint in Scott diagrams. Or a decimal point is too faint to be sure of.

[Jon Ketron]

After a long break due to outstanding restorations for others, I am back on this unit once again.  This time till completion.  Before starting back on the tuner, I wanted to tie up all other loose ends of this restoration. 

Power supply:  The power supply has already been fully serviced with a full set of replacement capacitors and resistors.  Both original Arcturus early 2A3 tubes test close to perfect, as well as the 5Z3 rect. tube.  I decided to ditch the 3 prong power cord.  A brand new high quality period gold rayon cord was installed.  Now we can call the power supply complete!

Jon

[Jon Ketron]

Jensen speakers were some of the finest available on the market in the 1930's.  Opinion:  Their quality and patented design could not be matched in the 1930's.  Very few manufactures used Jensen.  Several mass producers contracted to have Jensen speakers included with their models, very few though due to the high cost of the speaker itself.  Capehart used Jensen exclusively between the 1930's- and early 1940's.  McMurdo used Jensen exclusively as well thru the 1930's.  Ironically both companies had their electronics manufactured by the same company, Howard!  I find it interesting E.H. Scott deviated away from Jensen (partially) upon the introduction of the Allwave 23.  Both the late AW12 and all AW15 sets used 12'' Jensen pedestal speakers exclusively.  Upon this AW15 restoration, the 12'' Jensen had a yellow film of dust, dirt, and nicotine upon it's painted surface.  Above are before and after pictures of the speaker.  What a stunning piece of 1930's electronic history all by itself.  I find these speakers beautiful to look at!

 

Jon