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]

Thank you for the information Dave.  Looking forward to the end result.  I look forward to evaluating set performance and of course getting the chassis back into the cabinet.  Your AC-10 in Milford cabinet sounded great the several times we played it at your residence.

Jon
 

David C. Poland said:

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 remaining capacitors (Mica) as well as all resistors checked correct according to the schematic.  All resistors are close to or spot on to original values.  I would say all are within 10 to 20 percent tolerance and good to leave in the tuner circuit.

Seen below is the finished underside product made to look as close to original specs as possible.

Next up will be the top side!

[Jon Ketron]

Tuner top side has now been opened up.  Upon examination underneath the beautiful copper coil shield it appears a choke has been replaced.  Whom ever did the repair, performed a top job.  This component tested perfect disconnected out of the circuit as did the resistor beside it.  The large iron core choke shown tested perfect as well.  There is an air core choke within the circuit.  This replacement part is connected correctly according to the schematic.  I do not know where the original air core choke physically resided or what it looked like.  Upon further examination of the underside where the choke wire terminates, someone did a very neat splice when introducing the replacement into the circuit.  Two other capacitors upon the row of coils have been previously replaced.  They are of the ceramic type and test perfect.  Ceramic type capacitors are very hardy components and rarely go bad.  They tested correct value and have been left as is.  All original mica type capacitors on top of each coil test correct and are good to go.  This section of the tuner is hidden within the copper can.  As a result these replacements will be left as is since they are out of view.

[Jon Ketron]

With the copper can section completed, a full detail of the entire top side will take place.  This includes dismantling the front panel, cleaning and polishing the entire chassis, copper can, and front panel.  Cleaning of all variable condensers as well as tube sockets and switches/rheostats will take place as well.  One "Selectone" Bakelite transformer cover needed to be reset upon it's resting platform.  I carefully reamed out a very small track inside the cover.  Friction did the rest as the cover is now snapped back into place and held in very tightly.

[Jon Ketron]

The end result of the tuner:

[Jon Ketron]

Both the tuner and power supply are now complete and housed back within the cabinet.  All radio tubes are from my personal stock, test strong and are of the RCA/Cunningham brand globe type.

The cabinet will be detailed on a separate topic once the set is all back together and playing!

Jon

[Jon Ketron]

Both the tuner and power supply are interconnected via two sets of wiring harnesses.  Each harness has several wires contained within the loom of different gauge.  Both originals supplied by a good friend allowed me to create a mock up of a full set of near exact reproductions.  Wire insulation on the original harnesses are made of rubber and severely deteriorated.  A full set of reproduction harnesses (2nd picture below) have been custom made via a specialty company I went through.  The reproduction wires are cloth covered, a deviation from the original rubber material.  Sadly cloth was only available for this project.  I did my best to match all colors to the original harnesses.  Overall I am very impressed with the quality.  Spade lugs will be purchased and installed on each wire as seen within the originals.  These two harnesses are necessary for unit operation.  Seen below is a comparison of the original and reproduction.

[Jon Ketron]

The speaker for the AC-10 is a Rola manufactured speaker, model number D-90.  E.H. Scott labeled this speaker with a blue tag.  A very rare speaker to come across mainly due to the original E.H. Scott blue tag present.  I am very grateful to the friend whom sold me this speaker!  This speaker will need a complete overhaul.  First up will be a full disassembly of the speaker.  As seen below the speaker will need a new cone installed.  The spyder, pole piece, and audio transformer are in great shape.  The field coil and transformer pri-sec pass impedance checks and are good to go for operation.

[David C. Poland]

Caution to others. That copper cover must be carefully removed to avoid cutting a fine wire off each IF coil that runs to a lug on the coil form base.  Jon was fortunate as his example seems to have a little different arrangement than I recall.

For my receiver,   I seemed to have two of the several IF coils open. Actually, that fine bare non-insulated wire off  two of coils had been previously severed, no doubt by the sharp edges of the copper cover. Tricky repair due to the fine wire used in the winding .  ended up tack soldering I short length of 14 gage wire to the lug and succeeded soldering the fine wire to it.

*

The new cable will look great. All the AC is in the 4 wire cable - AC to the on/off switch and the heavy pair carry AC to all the 2.5 volt tube filaments.

[David C. Poland]

Caution to others. That copper cover must be carefully removed to avoid cutting a fine wire off each IF coil that runs to a lug on the coil form base.  Jon was fortunate as his example seems to have a little different arrangement than I recall.

For my receiver,   I seemed to have two of the several IF coils open. Actually, that fine bare non-insulated wire off  two of coils had been previously severed, no doubt by the sharp edges of the copper cover. Tricky repair due to the fine wire used in the winding .  ended up tack soldering I short length of 14 gage wire to the lug and succeeded soldering the fine wire to it.

*

The new cable will look great. All the AC is in the 4 wire cable - AC to the on/off switch and the heavy pair carry AC to all the 2.5 volt tube filaments.

[Robert Feenstra]

I need to know where you are getting the cloth cover for the cable.  I have not been successful in locating that nice of looking stuff!

[Jon Ketron]

Dave brings up a great point.  The AC-10 tuner I am working on had previously been serviced.  The last servicing included added extra length to the grid lead wires.  Such modification allowed for easy access second time around.

Jon
 
David C. Poland said:

Caution to others. That copper cover must be carefully removed to avoid cutting a fine wire off each IF coil that runs to a lug on the coil form base.  Jon was fortunate as his example seems to have a little different arrangement than I recall.

For my receiver,   I seemed to have two of the several IF coils open. Actually, that fine bare non-insulated wire off  two of coils had been previously severed, no doubt by the sharp edges of the copper cover. Tricky repair due to the fine wire used in the winding .  ended up tack soldering I short length of 14 gage wire to the lug and succeeded soldering the fine wire to it.

*

The new cable will look great. All the AC is in the 4 wire cable - AC to the on/off switch and the heavy pair carry AC to all the 2.5 volt tube filaments.