• Year
  • 1942–1944 ?
  • Category
  • Military Receiver
  • Radiomuseum.org ID
  • 71528

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Tubes
  • 3
  • Main principle
  • TRF with regeneration
  • Wave bands
  • Short Wave (SW only)
  • Power type and voltage
  • Dry Batteries / 30/4,5 Volt
  • Loudspeaker
  • - For headphones or amp.
  • from Radiomuseum.org
  • Model: Sweetheart 31/1 - MILITARY U.K. different makers
  • Shape
  • Portable set > 8 inch (also usable without mains)
  • Dimensions (WHD)
  • 110 x 28 x 143 mm / 4.3 x 1.1 x 5.6 inch
  • Notes
  • Frequency range 6-18 mc.

    This model was designed by the Norwegain engineer Willy Christian Simonsen (*1913, †2003) when he was working in the Radio Production Unit of the British War Office' Inter Services Research Bureau' (ISRB). About 50.000 units was produced (by Hale Electric Co. Ltd.?), at a price of just 8 GBP each. About 5.000 units went to the Norwegian government in exile, and were subsequently dropped over occupied Norwegian territory, intended for use by the resistance.

    The Sweetheart would still work when the HT voltage dropped to 20 Volt, allowing the HT battery to last for 150 to 200 hours, whilst the LT battery (4.5 Volt) had to be replaced approx. every 50 hours.

    Malcolm Haskard made a replica of this radio and & documented in HRSA Radiowaves, No, 129, July 2014. Photos and drawings have been  published with permission.

  • Mentioned in
  • HRSA Radiowaves, No, 129, July 2014
  • Author
  • Model page created by Ernst Rykkje. See "Data change" for further contributors.

 Collections | Museums | Literature


The model Sweetheart is part of the collections of the following members.


The model Sweetheart is documented in the following literature.


Forum contributions about this model: MILITARY U.K.: Sweetheart 31/1

Threads: 3 | Posts: 6

The Miniature Receiver OP-3 Type 30/1 is also often on the Internet incorrectly  referred to as "The Sweetheart". It's a dual band (MW & SW) superhet. A Superhet is not at all like a TRF or Regenerative radio. The case is similar but knob layout different: The "Sweetheart" is a 3 valve TRF regenerative set.


Michael Watterson, 17.Dec.12

Weitere Posts (1) zu diesem Thema.

The "sweetheart" radio was developed by  the Norwegian engineer Willy Christian Simonsen (1913-2003) when he was working in the 'Radio Production Unit of the British War Office'.

Following that, the "swetheart" was not manuactured by his own company "Simonsen Radio A/S" (Oslo) which he has founded in 1947.

It has to be precised where in the UK the about 50.000 units (from 1942 to 1944) was manufactured, and by whom.

Thank you very much in advance for any enlightment.

Best Regards,


Georg Richter, 16.Dec.12

Weitere Posts (4) zu diesem Thema.

I have built this in a small eddystone box using 3 x AA cell for filament, 3 x 1j24b tubes instead of 1T4 and 10 x CR2032 coin cells for HT. A modern "crystal" earpiece and miniature "polycon" capacitors from transistor AM radio. The coil is miniature AM radio Ferrite Aerial coil unit with an extra winding added.

So I redrew the schematic in "Eagle" from the original. It's all the original values and wiring but the 1j18b instead of 1T4 (DF91) pin connections.

I beleive the original 30V battery is a Hearing aid type, or possibly 2 x 15V hearing aid types. I have got a wiring error so have not yet tested my replica. The external Aerial and Earth connections use TO220 transistor isolating washers to insulate terminals from the case.


Michael Watterson, 16.Dec.12

Weitere Posts (1) zu diesem Thema.