Olson RA-48

Olson RA-48 Receiver

The Olson RA-48 was made in Japan for Olson Electronics. What attracted me to this set was its size and its nice design. The set's tuning dial and design are similar to the Hallicrafters S-119 Sky Buddy II. It is only 9 1/2 inches wide, about 2/3 the width of comparable small sets. Despite its small size, it is very well constructed. The set is not listed in Osterman's "Short Wave Receivers Past and Present" (3rd edition). However, in its "Briefly Mentioned" section, the book shows a Unica UNR-30 that is the twin of this Olson radio. The Unica was sold in England in 1968 according to Osterman who questioned whether it may have been made in England. Both the Unica and its Olson twin were made in Japan. (See JA1VHZ's info and pictures of the Unica UNR-30 .)

Olson RA-48 receiver (42k)

Frequency coverage is 550KHz to 30 Mhz in four bands. It is transformer operated and single conversion with an IF of 455 KHz. The set has 4 tubes including a 6BE6 oscillator, a 6BA6 IF amplifier, 6AV6 for detector/ first audio, 6AR5 for audio output. It uses a half wave diode rectifier. The BFO is regenerative and variable. I was surprised at how well the BFO worked with such minimalist circuitry when carefully adjusted. While the tuning is a vernier drive, the lack of bandspread makes tuning a bit difficult for SSB. However, I did listen to a few SSB exchanges on 75 meters. The BFO can also be used to boost the sensitivity of the set for standard AM signals in a manner similar to that of a regenerative set.

Olson RA-48 chassis (42k)
Compare the size of the small power and output transformers and tuning cap to the vacuum tubes.

In good electronic condition
This radio was in very good cosmetic condition. The volume and BFO controls have been replaced. I powered the set up slowly to reform the electrolytic. The set began working rather well. All of the alignment points still had the original white paint-locks on (a bit of paint was used to keep each alignment screw adjustment in place for shipping and to make it obvious if the radio alignment had been "diddled" with.) Since the radio played very well and seemed to be in reasonable alignment, I decided to leave it at those factory settings.

Olson advertisement
The RA-48 was advertised in several Olson "flyer" catalogs in 1968.

1968 Olson ad for the RA-48 (43k)

This example is serial number 121. I believe the RA-48 to be relatively rare. If you own one, let me know what serial number is on yours. If you have the schematic, please scan for reference for other owners.

Notes from other RA-48 owners

Compared with Knight Span Master II
Allied Radio advertised a similar Knight "Span Master II" shown in this 1970 Allied Catalog picture. In design, it appears to be almost a mirror image of the RA-48. However, the Span Master II uses 5 tubes of the "All-American 5" AC-DC series filament variety (12AV6, 12BA6, 12BE6, 35W4 and 35C5 in place of the usual 50C5). It includes an isolation transformer that I assume also drops the voltage for the series string closer to the Japanese standard of 100 volts. The IF transformers and certain other parts are identical to those in the RA-48. It was available in kit form and is likely from the same Japanese supplier. As noted, the design for both appears to be inspired by the Hallicrafters S-119 Sky Buddy II. That makes me wonder if the S-119 also had a Japanese parts supplier connection.

Knight Span Master II

A Measurements model 59 grid dip meter was the previous item on the bench.

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