The early rig, the HW7, was a much simpler design, and, although it was useful on the transmit side, the receiver was very much a compromise to say the least. Both the HW7 and HW8 are direct conversion by design, but the HW8 is far superior, using mixing circuitry. Both are CW only rigs, and a number of modifications have been published for them. There is a useful book, which has a wealth of well proven ideas to improve the rig, and data sheets are available from the G QRP Club for articles on the HW8 published in Sprat.
Power output on transmit is quoted as 2 watts and the rig draws 430 mA on transmit and just 90 mA on receive from a 13.8 volt DC supply. Bands covered are basically the CW portions of the 3.5, 7.0, 14.0 and 21.0 mHz bands. Audio filtering is included (two 741 op amps) are useful inclusions. The size of the HW8 (9.25 x 8.5 x 4.25 ins) and weighing in at 4 lb, makes it a popular rig for portable and mobile home use.
Expect to pay about £80 for a clean HW8 on the UK second hand market.