About the Admiral 7P35N Portable Radio
Admiral 7P35N was a "portable" AM radio, designed an built by the Continental Radio & Television Co. of Chicago, Illinois. This radio qualifies as portable as it can be powered both from Household Current or by battery power.
The Admiral 7P35N is a post WW II radio that was first released to the consumer market in 1947. This radio is of Superheterodyne design and covers the standard AM Broadcast Band (540 - 1600 kHz).
The Admiral 7P35N is of "transformerless" design, feeding the Household Current though a Selenium rectifier, filter capacitors, and a resistor network in order to provide the 90 Volts DC to the electron tubes. Electron tube filaments are connected in series and are supplied 9 Volts DC. This design makes this radio very dangerous to work on when powered from AC Household Current as the chassis could be connected to "Hot" depending on how the non-polarized plug is connected to a wall outlet.
A switch allows you to use an internal battery to power the radio. An internal label specifies the battery of choice is an ENSIGN AB50 which supplied the required 90 and 9 Volts DC needed for operation.
Below is the complement of electron tubes installed in the Admiral 7P35N and their purpose:
1U4 = RF Amplifier
1R5 = Mixer/Oscillator
1U4 = IF Amplifier
1S5 = Detector/Preamp
3V4 = Audio Amplifier
The Admiral 7P35N comes in a smart looking leather case with a Bakelite handle. A protective flap covers the tuning and volume knobs, speaker grill, and tuning dial when not in use.
Access to electron tubes and battery compartment is achieved through a hinged back cover.
A label on the inside of the hinged back cover indicates chassis layout with electron tube positions, suitable household currents, and a chart of compatible replacement batteries. An interesting feature of this and many radios from the 1940s is that if could be powered from both DC or AC household current as both were available in the United States at the time. DC household current was eventually entirely replaced by AC.
About the Continental Radio & Television Company
Ross Siragusa founded the Continental Radio and Television Corporation in Chicago during 1934. Admiral Corporation was a subsidiary of Continental Radio and Television Corporation of which consumer electronics were marketed.
In addition to the Admiral name, Continental Radio and Television Corporation marketed their products under the Globe Trotter, Radiomaster, and Star Raider names.
During WW II, electronic equipment was supplied to the military under the Admiral brand.
Admiral branded televisions were a top seller during the "Golden age of Television", which spanned from 1947 to 1960.
Successful television sales allowed the company to branch out into large appliances, such as washers and refrigerators, in the 1950s.
Admiral Corp was also successful in moving product through major sales outlets such as Montgomery Ward and Sears.
In 1960, its heyday, Admiral Corporation boasted sales of 300 million and employed 8,500 people with four manufacturing plants.
Like many American consumer electronic companies in the early 1970s, Admiral Corporation hit hard times due to electronics dumped on the US market from Japan.
Rockwell Automation purchased the company in 1973, they proceeded to sell off large appliance manufacturing operations to Magic Chef. This division was later sold to Maytag and finally to Whirlpool. Whirlpool now markets the Admiral brand exclusively through The Home Depot chain.
In the 1990s Admiral branding was being used on Zenith products. Currently television business continues under AOC (Admiral Overseas Corporation) International that sells LCD and HDTV appliances.
The Admiral name lives on, but is used to rebadge large appliance and consumer electronics manufactured by other corporations.
Please stop by radioboatanchor.com in the upcoming months to see updates on the restoration of my newly acquired Admiral 7P35N Portable Radio.
I love to frequent rummage sales during the winter and garage sales during the summer, looking for vintage radios to restore and add to my collection. I happened across this GE 10-Band Portable Radio in the "Free" bin on the last day of a local rummage sale and decided to give this radio a good home.
This GE 10-Band Radio had many issues upon initial inspection:
- The metal tuning dial scale broke free and was just sitting behind the tuning dial window.
- The Band Select and UHF Faceplates also broke free and were sitting inside the tuning dial window.
- The metal Memory Log scale came unglued from the cabinet front.
- All of the screws holding the back cover were missing, it was just snapped in place.
- The antenna tip was snapped off.
- The original volume knob was missing, the orginal plastic knob was replace with a brushed aluminum one.
- The silver paint around the tuning dial window that was once was emblazoned with the GE logo was completely worn off.
- The vinyl cladding on the AC electric cord has become so brittle with age that I was unable to unravel it from case in the battery compartment.
Despite all of its issues, I knew that this radio could be successfully restored.
About this Radio
The General Electric Model 7-2971A 10-Band Portable Radio was a multi-band analog radio offered to consumers starting in 1975. Through research, I discovered that it was still for sale in 1979 as it was advertised in a Popular Mechanics magazine of that year. The price of this radio in 1975 was $120, or about $500 today adjusted for inflation. This radio was of the standard Super-Heterodyne design and covered the following bands:
AM Broadcast 540 - 1600 kHz
FM Broadcast 88 - 108 MHz
CB: Ch 1- 40 (27 MHz),
UHF: 448 - 512 MHz,
SW1: 11.8 - 21.9 MHz,
SW2: 5.1 - 9.9 MHz,
PS-LO: 30 - 50 MHz,
PS HI: 150 - 174 MHz
Air: 108 - 136 MHz,
Weather: 162.40 - 162.55 MHz.
This radio has a separate tuning control and dial indicator for UHF. Weather station tuning is done blindly with a thumbwheel located on the back cover.
Pushbuttons on top of the radio control access to UHF, CB and Weather bands.
The General Electric Model 7-2971A incorporates three antennas, an internal loopstick and groundplane antenna. In addition, it has an external telescopic whip antenna.
Being portable, it could be powered by either 120 Volts AC household current or six D cells.
Back Cover Removal
Access to the internal electronics of General Electric Model 7-2971A is done by removing the back cover. You must remove five screws (circled in red) on the back cover and one inside the battery compartment. As mentioned, all of the back cover screws were missing from my radio. Be careful when removing back cover as there are two wires that connect the battery compartment to the printed circuit board.
The craftsmanship of consumer electronics from the 1970s leaves much to be desired, parts are haphazardly installed in the single sided printed circuit board, jumper wires everywhere. The parts in the RF section are covered in wax, I assume to prevent vibration oscillations to occur when the radio is transported or set down.
Printed Circuit Board Removal
The printed circuit board will need to be removed, in order to fix the tuning dial scale, Band Select and UHF faceplates that have broken free.
The first step to printed circuit board removal is to remove the Tuning, UHF Tuning, and Volume knobs. They are of "push on" type and can be pulled off just as easily.
You will also need to remove the Band Switch knob, it is also of the "push on" variety and can be pulled off easily.
Don't forget to remove the Squelch knob located on the top of the radio.
The leads of the power transformer are soldered to the printed circuit board. The power transformer will need to be removed with the printed circuit board. You will need remove the screws, circled below, in order to free it.
In addition, you will need to remove the screw circled below to free the AC Power Cord that connects to the primary winding of the power transformer.
Desolder the connections to the speaker and external antenna. Locations are circled in the picture below.
Time to remove the screws holding the printed circuit board in place. I circled their locations in the picture using magenta so that you could see it against the red printed circuit board. Check carefully, there may be screw locations that I missed as some of the screws holding the printed circuit board in place were missing.
There is a control panel mounted inside the top of the cabinet. Attached to it is a Headphone jack, and controls for Squelch, Bass, Treble. The jack and controls on the control panel are hard wired to the printed circuit board. In order to access the control panel, you will need to flip the main printed circuit board 180 degrees towards the top of the radio cabinet. Circled below are the locations of the screws holding the control panel in place.
Finally, the printed circuit board, power transformer, and control panel can be removed from the cabinet.
Fixing the Tuning Dial Scale and Faceplates
As mentioned, the main tuning dial scale came unglued at some point. I used E6000 Industrial Adhesive to glue the main tuning dial scale back onto its mount.
The Memory Log scale also came unglued.
The Memory Log scale proved challenging to fix. First, I had to completely remove it then scrape all of the remaining glue from the underlying mating surface. In addition, I had to straighten and flatten the Memory Log scale then lightly sand the back of it to remove all of the old adhesive.
I then applied a bead of Super Glue to the back of the Memory Log scale then pressed and held it in place for several minutes until the glue set.
The Band Select and UHF Faceplate also came unglued. They were located in the areas circled below.
Gluing the Band Select and UHF Faceplate was a little more tricky. I had to apply E6000 Industrial Adhesive to the back of the faceplates then maneuvered them in place from behind the main tuning dial window. I then used a screwdriver to press them in place.
Volume Control Repair
A previous owner replaced the Volume Control potentiometer but did a lousy soldering job on the connections. Below is a picture after I desoldered the connections, stripped the wires, then re-soldered connections to the potentiometer.
As with many older radios, the end cap had broken off of the external antenna.
Finding a direct replacement antenna for vintage radios can be challenging.
I replace missing antenna end caps with pieces from my daughter's LEGO set. Don't worry, she won't miss the few pieces I appropriate as she has many more.
Gluing the LEGO piece to the end of the antenna will not provide enough tensile strength and it will eventually come off. I drill a small hole through the antenna end and LEGO piece then drive a small terminal pin through it.
I then cut the ends of the terminal pin flush with the LEGO piece and add a dab of Superglue at entrance and exit holes to keep it from coming out.
The vinyl cladding on the original power cord had grown stiff and brittle with age. I cut the power cord off to make handling the printed circuit board easier. It will be replaced during reassembly.
Electrolytic Capacitor Replacement
As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. As a rule, I typically replace electrolytic capacitors in vintage electronic equipment. Electrolytic capacitor replacement will prove difficult on this radio, as you will have to remove the tuning dial mount and dial cords, in order to gain access to the foil side of the printed circuit board. In addition, stringing the two dial cords during reassembly would prove a nightmare.
I decided against replacing electrolytic capacitors in the General Electric Model 7-2971A. Through bench testing I determined that the electronics of this radio worked perfectly without electrolytic capacitor replacement. There was no tell-tale hum of failing filter capacitors when powered by AC house current. It worked perfectly under battery power as well.
I use Labelle 107 oil to lubricate all of the pulleys for the tuning dial indicators. This oil is safe for plastics. I have this oil on hand for my model train hobby.
I use Labelle 106 Grease to lubricate the gears for the Band Select indicator.
With the electronics removed, I took the opportunity to detail the cabinet of this radio. I use many car care products for cabinet detailing. Meguiar's PLASTX works great for removing fine scratches from the tuning dial window.
Armor All Protectant works great for cleaning and shining the cabinet and back cover. I used the Advance AutoParts equivalent of Armor All.
The felt filter over the vents in the back cover had disintegrated due to age. I replaced with a rectangular piece of Speaker Grill Cloth.
The silver paint around the tuning dial window had completely worn off. I carefully masked the area off with Frog Tape then wiped the area to be painted with denatured alcohol to remove any grease residue.
I sprayed the area with three coats of silver paint giving time to dry between coats to avoid runs or sags.
Here is the finished product. My only regret is that I had no way of stenciling the GE logo that used be in the lower left corner of the silver painted area.
I also use Meguiar's PLASTX and an old toothbrush to clean up buttons and knobs.
Reassembly is the reverse process of disassembly, you must first attach the control panel mounted inside the top of the cabinet before installing the printed circuit board. Make sure you reinstall the push buttons at the top of the printed circuit board before installation, if you took them off for cleaning.
Make sure you solder the yellow and orange wires to the speaker. In addition, a small polyester capacitor is connected between the speaker terminal with the yellow wire and the main tuning capacitor.
I replaced the power cord with non-polarized one I cut off of a broken Soldering Iron. I stripped the transformer and power cord leads then soldered them together.
I then used heat-shrink tubing to cover and insulate the soldered connections.
Solder the white antenna wire to the solder lug located at the base of the external antenna.
One screw at the base of the antenna holds it in place.
Two screws hold the power transformer in place.
The power cord is channeled through cavity on the inside of the cabinet that provides strain relief. It is topped with a piece of insulating fish paper that is held in place with a single screw.
Green and black wires from the printed circuit board connect to the battery compartment, built into the back cover. The green wire goes to the positive terminal and the black wire goes to the negative terminal of the battery compartment. I extended these wires, allowing me to sit the back cover flat beneath the radio cabinet.
Install all of the knobs on radio. All of the knobs are keyed so you can't a mistake when installing them. As mentioned, a lot of the original screws for this radio were missing. I had to search my junk box for suitable replacements.
You will need to thread the power cord through the hole in the battery compartment of the back cover. Carefully install the back cover on the cabinet, making sure you don't crimp any wires where they mate. Six screws hold the back cover in place. One screw hole is located in the battery compartment.
Make sure you attach the pointers on the Memory Log. Also install the battery compartment cover.
Below is a picture of the finished product!
My recently restored General Electric Model 7-2971A 10-Band Portable Radio in action!
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
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