In 2012 I built a so called Whaddon MK VII Paraset."Paraset" contains the words "radioset" and "parachute". The Whaddon MK VII was built in Whaddon/England during World War II. It was designed for the MI6 and SIS secret service. They were used for clandestine radio operation in the countries occupied by the Germans. So we are talking about a spy radio-set for resistance groups. Some of the operators were radio amateurs! Made to be dropped by parachute, the parasets had to be very rugged. There were versions in wooden boxes, and also the "cake box" version made of nickel plated steel. The morse key is built in. There were flexible mains supplies as well as vibrator supplies creating the 350V anode voltage by a mechanical vibrator from a lead-acid car battery. The output is about 5W. The built in tuner can accept various lengths of random wire. The frequency coverage is 3.3 - 7.6 MHz.
The transmitter is a crystal controlled power oszillator using a single 6V6 steel tube. The wartime crystals (DC-35 or FT-171b) were very large, so they could withstand the high current present in this oszillators. With modern small crystals it can be a problems. Somtimes the crystals get damaged, and you get "jumps" of a few 100 kHz when they moan of the high current.
The receiver is a 2 tube regenerative receiver with 2x 6SK7 steel tubes. It can accept high impedance electro-mechanical headphones (2000 Ohms). I built my Paraset band spreaded for 40m. See the small foil trimmers visible in the picture. I had to remove this trimmers and look for better substitutes, as they destroyed the Q in the receiver parallel circuit. The original receiver had several MHz spreaded over a 180 deg. scale! The receiver is very sensitive, but due to a great bandwith the operation gets difficult when the band is crowded. There is no plastic isolated wire inside this replica. The coils are wound on paxoline tubing with DSC (double silc covered) wire with a lot of shellack to fix the windings. Some parts are really wartime items, some are "vintaged" modern parts.
This is not a collectors radio...I use it on the air! In the crowded 40m band it is not so easy to run a QSO. At first I insert the crystal in a separate oszillator and tune the receiver to the crystal frequency. Then I plug the crystal in the paraset and start my CQ call. Sometimes I loose a QSO as another QSO starts in the big window the receiver covers. QSOs with other QRP stations proove that the receiver is really sensitive. All you need is a not too crowded band...
Look at the new knobs.