ELECTRICAL RESTORATION: E.H. SCOTT AC-10

[Jon Ketron]

This restoration topic will cover an electrical restoration of the rare E.H. Scott AC-10 radio set.  Prior to the chrome years, preceding sets including the AC-10 were offered through custom set builders or kits supplied via E.H. Scott (then called Scott Transformer Co.) between the early 1920's through 1930.  While E.H. Scott offered the set to the consumer, they did not offer assembled sets direct due to then current RCA Superhetrodyne patents controlling the sale of the Superhetrodyne circuit.  E.H. Scott would contract through custom set builders (popular at the time) to have these radio units built for the customer.  I find this part of E.H. Scott history fascinating!

Not a cheap set by any means when sold new, the AC-10 was a high quality unit for the time it was introduced to the market.  The AC-10 consists of a tuner chassis, separate power amplifier, and E.H. Scott labeled Rola speaker.  There were several AC-10 versions offered between 1929-1930.  The set shown below is a late version, circa 1930.  Two sets of wiring harnesses connect both tuner and power amp together.  These cabled are already in the works of being replicated to look very close to or near exact copies of the originals.

I find the AC-10 a very attractive set, especially with it's copper coil shield along the back of the tuner.  AC-10's surface from time to time, complete example's are rare to come across from what I have seen within the hobby.  This example shown below is period correct.  Many thanks to the two gentlemen whom have allowed me to acquire the parts to make a complete set.

The cabinet this receiver will be housed in will be discussed in a separate topic you will not want to miss.  More on that later in a separate topic!

Thanks, comments welcome!

Jon

[Jon Ketron]

There are three variations of the AC-10.  Each variation has a different layout when it comes to the power supply.  The variation shown below utilizes three radio tubes:  Two type 45 output tubes and one type 80 rectifier tube.  This power supply looks to have never been serviced.  All wiring is of the rubber type and needs to be replaced.

Jon

[Jon Ketron]

Full resolution photos:

Jon

[Jon Ketron]

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[Jon Ketron]

Full resolution photos:

Jon

[Jon Ketron]

The goal of this restoration is "replication" to as close as possible original specs and layout.  As previously mentioned, all rubber wiring within the power supply will need to be replaced.  After 80+ years, most of the original wiring has cracked and become very brittle.  This set will become a daily player once again and requires a full servicing to work at it's full potential.

With the goal of replicating as close as possible original specs and cosmetics, I had inquired about a type of wire which would closely resemble the original wiring present.  Appreciative of Norman's advice, I was steered toward silicone rubber insulated test lead to re-create the look of the original rubber wiring.  I agree with Norman, this silicone rubber test lead is near spot on to what the original wiring looks like.  Original wire colors are faded with age, so colors may not match perfectly to what we see today.  I would like to think such original wiring was once vibrant with colors as displayed in the picture below.

So far the wire replacement program for the power supply is going as planned.  1/2 of the Power supply has now been re-wired with silicone rubber insulated test lead.  I highly recommend such wire type.  Each new wire piece has a gauge stamp on it, temp rating, and voltage rating.  Such print can be removed via rubbing alcohol if desired.

Jon

[Jon Ketron]

Before completing the re-wiring of the entire power supply underside, the capacitor pack needs to be addressed.  Upon starting the electrical restoration, I was able to locate both tuner and power supply schematic diagrams via "Citizens Radio Callbook" circa March 1930 edition.  Once traced out, I have come to the conclusion that the large middle can on the power supply top side houses six 2.0 MFD capacitors.  All of these capacitors have been replaced.  I gut the can of original caps, re-stuffed with six non polarized 2.0 MFD values rated to 630V.  A new Rubber grommet and new rubber wiring were utilized to incorporate a reproduction of the original look.  Once all the capacitors were installed within the can, the bottom was soldered shut just as it had been before.  The original black paint on the capacitor can has seen better days.  I plan to repaint the can black to look near identical to the two originals on the chassis.

Jon

[Kent King]

Very nice work!

[Jon Ketron]

Thank you Kent.

All rubber wiring on the power supply has now been replaced.  There were two gauges used by E.H. Scott in this power supply, 16ga and 18ga.  I replaced all wiring accordingly.  I matched each wire color to the original replaced.  I checked impedance values of all transformers and chokes.  Everything checks good!  Capacitor pack now has a fresh coat of black paint installed.  Looks very close to original paint on other two metal cans and chassis.  A new reproduction twisted pair 18ga USA made cotton braded AC power cord was installed to look identical to the worn out original that was once in it's place.  I re-used the original plug to give an even more original appearance.  Type 80 rectifier and two type 45 output globe tubes have been tested and ready for installation.  Globe style tube technology is what you would have seen on a set of this vintage as ST style tubes were introduced to the market several years later, between 1931-1932. 

Power transformer restoration complete!  On to the Tuner!

Jon

[Jon Ketron]

The AC-10 tuner is a rather interesting piece.  Most mass produced tuner chassis in 1929-1930 are of a steel design.  Philco for example in 1929-1930 would have used a stamped steel chassis.  The base plate of the AC-10 is made of a non metal material. The coil shield along the back of the tuner is made of copper.  The AC-10 had a major edge over the mass produced sets in 1929-1930.  The AC-10 was a Superhetrodyne circuit!  Superior in every way to all competition during the time frame, except RCA whom held the Superhetrodyne patent.  I find the AC-10 tuner chassis to be of solid design, very appealing to the eye as well.  This AC-10 tuner is a late version with small dial escutcheon and appears to be untouched just as the power supply was.

Note:  A remote control unit was an E.H. Scott option available to the consumer while this set was offered on the market.  A modified AC-10 to my knowledge would be needed for remote operation, offered through E.H. Scott.  The remote feature was not motor driven, rather the remote utilized a set of coils with push button and cable to control remote station selection.  Interesting to note Kolster's top of the line K-45 issued right around the same time featured a remote control function, as did RCA's top of the line RAE-68 in 1930.  Several manufactures were in competition over the remote feature in the early days.

[David C. Poland]

FYI - as with other Scott models, the AC10 evolved with little changes during the couple year production - most notable; the front escutcheon and tube arrangement of the 24's and 27's. Kent and I had 3 examples which we put side by side right side up and then upside down. Initially, it was offered as a kit, but very soon, Scott commenced manufacture. It is also Scott's first ground up socket power radio. 

The AC10 is a really sensitive radio, provided you moved both the center dial knob and the left side control (antenna resonance) together to maintain peak sensitivity. Sounds good too with that 10 inch pedestal speaker (a Scott tagged Rola) mounted in a cabinet - and Jon has a superb cabinet for it.

[Jon Ketron]

All capacitors will be "re-stuffed" with brand new components housed inside the original components.  First up will be all three bathtub capacitors on the tuner underside.  All three are of the Potter brand, a parts manufacturer E.H. Scott utilized for quite a few years moving into the Chrome years.

Upon inspection, it would seem someone had already taken the liberty of re-stuffing the three original Potters!!!

These replacement caps appear to be sealed in a paraffin wax product, not the original type of pitch used.  All three have been re-stuffed with brand new correct rated capacitors.  Each was sealed with black hot glue to simulate the tar pitch look.  Tar would have been the original material used. 

[Jon Ketron]

There are two other potted type capacitors utilized underneath this tuner.  Sprague type .1 MFD foil capacitors potted in wax.  Both of these caps had their internal components removed, re-stuffed with brand new correct rated capacitors, then sealed with black hot glue to simulate a tar pitch look.  I was not able to salvage enough wax to re-seal these two capacitors with their original product.  I did my best to maintain a period look.  Tar was a very popular type of pitch material used in capacitors between the 1920's and 1930's.