R106: HRO Senior Model M

 

 I repaired some minor faults many years ago and since then my brother-in-law, Riki, kindly gave me the set.

 

 The receiver uses UX-based American valves having standard 6.3 volt heaters, although earlier models used similar valves with 2.5 volt heaters. I'm not sure why these latter types were selected because, with an external power unit, resistive losses would be more critical.

The 6.3volt UX valves are basically the same as the IO types: 6D6=6K7, 6C6=6J7, 6B7=6SQ7 and 42=6V6, The 6D6 is variable mu allowing the AGC to change the stage gain.

 

 The receiver has had only one modification carried out which is the addition of an audio output transformer. I'm puzzled why an internal transformer wasn't included on the main chassis in the original design because, apart from an external transformer being poor practice, it could have been used for better headphone matching with extra audio power.

 

 
 This label is on the inside of the hinged lid.

 
 This label is on the underside of the receiver.

 The power supply that arrived with this HRO, I believe may have been made by the late G3AQY and the pictures show that it isn't what it first seemed. The original HRO PSU was this shape and was referred to as a "Dog House" power supply, but removing the cover reveals more parts than the original.

 

 There are three valves: A 6V6G, EF80 and 0D3/VR150.

 

 Inspection of the wiring revealed some silicon diodes (covered by black sleeving) wired to unused pins on the 0D3 stabiliser valve. Without tracing the circuit I believe it's a regulated HT supply with a potentiometer for setting the HRO HT voltage. A separate heater transformer for the 6V6 & EF80 is located adjacent to the pair of blue condensers. The loudspeaker is wired to the jack plug on the front of the PSU and needs a cable wired to the rear of the R106 to where the new output transformer connects.

 

 

 HRO Coils at the Radio Museum

 

 Range

 Marked

 Notes

 50-100Kc/s

-

R106 

 50-100Kc/s

 -

 SSB HRO 

 100-200Kc/s

-

R106 

 100-200Kc/s

 H657

 SSB HRO

 180-430 Kc/s

-

 R106, White on black label

 180-430 Kc/s

 H503

 SSB HRO

 0.48-0.96Mc/s

 267

R106

 0.48-0.96Mc/s

 H952

 SSB HRO

 0.9-2.05Mc/s

 H520

R106 

  0.9-2.05Mc/s

 E331

 SSB HRO

 1.7-4.0 Mc/s

-

 R106, White on black label

 1.7-4.0 Mc/s

 B94

 SSB HRO

 1.7-4.0 Mc/s

 H619

 HRO Junior

 3.5-7.3Mc/s

-

 R106, White on black label

 3.5-7.3Mc/s

 D296

HRO Junior

 3.5-7.3Mc/s

 H611

 SSB HRO

 7-14.4Mc/s

 H658

 R106

  7-14.4Mc/s

 H753

HRO Junior

 7-14.4Mc/s

 D339

 SSB HRO

 14-30Mc/s

-

 R106, White on black label

 14-30Mc/s

 J386

 SSB HRO

 10m

H673, 14-30Mc/s 

 Bandspread

 15m

100-200Kc/s

Bandspread SSB HRO 

20m

-

 Bandspread SSB HRO

 20m

-

Bandspread SSB HRO Transceiver

 80m

-

Bandspread SSB HRO Transceiver

 

 Below: the HF coil packs with the R106
 

 More sets of coils
 
 

See another HRO

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