Sears Wayfarer Model 8227 Multiband AM/FM/SW & LW Radio
This is a brief tour of the Sears "Wayfarer" Model 8227 Shortwave Radio.
The Sears Model 8227 Wayfarer is a Sears-branded, Sanyo-manufuctured multiband portable as indicated by the "564" prefix on the chassis number. (Another clue are all the Sanyo-stamped components including the speaker inside the radio!)
This fully Solid State radio is capable of receiving:
- Long wave (LW)
- Medium wave (MW)
- Shortwave (SW) in three bands and
- the commercial FM broadcast band
This means it covers the 160 - 190 KHz license-free 'freeband' spectrum allocated and the the aircraft and marine NDB (Non-directional Beacon Band) band as well as the domestic commercial AM Broadcast band and the international shortwave bands.
Here is the 'band stack-up' from LW through Shortwave:
It can be seen the that coverage is as follows:
And here is how the radio tuning 'dial' is actually laid out:
This is a rather large 'portable' as can be seen in contrast to the 19" rack-mountable test equipment seen behind the Sears Wayfarer on the bench in this picture:
As was mentioned, this Sears portable radio is manufactured by Sanyo. After some digging around on eBay I managed to find this unit - a Sanyo branded "Transworld" Model 18H-815.
As it turns out, the RF board in the Sears Wayfarer is, with a few minor exceptions, identical to the RF board in the Sanyo Transworld. I discovered this after some amount of troubleshooting on a Sears Wayfarers and while using the Sanyo as a 'reference' for DC voltages and low-level audio signal levels on the main RF board. (It should be mentioned at this point that the Sanyo uses an entirely different audio Power Amplifier stage.)
A couple of observations on the Sears Wayfarer (and Sanyo Transworld, because of the lineage)
When working properly:
- Excellent AM Broadcast Band audio fidelity (especially when the AM IF is tuned for b_r_o_a_d
rsponse!)
- Excellent sensitivity (on the AM broadcast band at least owing to a LARGE ferrite rod antenna)
Problems:
- The AC Power Supply (a separate board in the Sears Wayfarer; a separate enclosed 'module' -which still works- in the Sanyo Transworld), with age, is prone to failure.
This has been due to failures of (as I have observed during troubleshooting of a couple of Wayfarers): 1) the Power Supply's large electrotytic capacitor and 2) an open Zener diode.
In both failure modes the radio will 'hum' noticably, in the case of the main power supply capacitor failure the radio's audio output will be noticably 'limited' (easily maxed out).
The three transistors in the power supply survived each of these failures; I performed several tests on each of these devices after removing them from the Power Supply board in the Wayfarer:
- Iceo (Leakage current, Emitter to Collector, Base open) at 5, 10 and 15 V
- Ices (Leakage current, Emitter to Collector, Base connected to Emitter) at 5, 10 and 15 V
- Breakdown voltage - to about 20 Volts
- Quickie DC 'gain' measurement
Circuit setup
- either a 10 K or a 100 K resistor from Base to a -5 V supply
- 470 resistor from Collector to the same -5 V supply through an ammeter
Observe:
- Collector current
- Collector voltage
The test results were consistant with what is to be expected of Ge PNP devices; i.e., measureable leakage currents and moderate gain. Subsequent breadboarding showed that the devices were operable in the Power Supply circuit with expected nominal results.
A replacement of the 'error amplifier' stage (a 2SB187 device) with a PNP Si device (a 2N2907A device) resulted in almost a factor of 10 reduction in output voltage change with input voltage change.
- Critical electrolytic capactors fail with age
These failures can cause substantial loss of audio levels, and/or various 'distortion' elements such as excess low-frequency distortion on received AM stations (such as when the electrolytic capacitor on the AGC line dries out!)
References:
- A tutorial on the principles of radio receiver design.
"THE SUPERHETRODYNE TRANSISTOR RADIO"
my.integritynet.com.au/purdic/am_rec.htm
Shown on this site is a schematic of the typical transistorized AM Broadcast receiver using the 'homodyne' mixer/oscillator stage.
- Transistor radio mini-history
www.etedeschi.ndirect.co.uk/tr.radio.history.htm
Excerpt:
... back in Japan not all was peaceful and quiet. A small tape recorder manufacturer called TOKYO TSUSHIN KOGYO LTD. managed in 1953 to convince the Japanese Minister of Trade and Industry (MITI) to let them acquire the transistor manufacturing licence from WESTERN ELECTRIC and the Bell Laboratories patent.
After some struggle to understand and learn the technology and the manufacturing process (the Western Electric licence did not include the know-how) TOTSUKO (as SONY was known at the time) managed to produce their own transistors and, in August 1955, their first coat pocket size transistor set (the model TR-55).
...
At the beginning of the sixties Japanese manufactured sets became even smaller by reducing the size of their components and by cleverly redesigning their electronics circuits so as to be able to use lower levels of voltage and current and therefore smaller batteries.
...
at the end of the decade by using the INTEGRATED CIRCUIT, the new solid state device which combined transistors and passive components in the same package.By about 1963 it was all over.
The Japanese invasion had killed off many American manufacturers and even glorious names like RCA, General Electric, Philco etc. were forced to use Japanese made components or to have their sets made in Japan altogether. Some of the Japanese transistor radios had to bear American sounding names in the effort to disguise their origin for the hard core nationalist consumer. Brand names like "Trans American", "Americana", "Lafayette" and more were nothing else than sets made in Japan.
- How to date early Japanese tr radios
www.etedeschi.ndirect.co.uk/howto1.htm
- Earl Diamond and RCA Radio Indianapolis in the 1960s and 1970s
www.transistor.org/feature/diamond/earldiamondfeature.html
Opening intro:
Earl Diamond is an electrical engineer who worked for RCA's radio division in Indianapolis, Indiana from 1962 until RCA ceased its radio manufacture in 1974 and closed the division. During his tenure at RCA, Mr. Diamond designed several well-known RCA portable transistor radios and was kind enough to grant me an interview.
- Conrad Jutson and General Electric's Radio Receiver Department, Utica, NY, 1959 through 1966
www.transistor.org/feature/jutson/interview.html
Opening excerpt:
I had the opportunity to interview Mr. Jutson for this article, and he kindly allowed me to copy some GE literature he had. This interview grew out of some correspondence we had regarding the P780, a formidable AM radio which GE manufactured from 1960 to at least 1965. Mr. Jutson played a significant role in the development of this radio, which offered extraordinary performance, durability, and battery life.
- THE TRANSISTOR MUSEUM
semiconductormuseum.com/Museum_Index.htm
"Dedicated to Preserving the History of the Greatest Invention of the 20th Century"
- THE TRANSISTOR RADIO DIRECTORY
www.geocities.com/aldoandr/transistor.html
LARGE list of links!