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All sorts of interesting stuff about Ham Radio and old gear from Steve G3ZPS, near London in the UK

KW201, KW Vespa, KW160

KW started out making separate transmitter and receivers for 50s UK Hams mostly running AM. The ispiration and indeed some of the components came from the Italian Company Geloso. All this early AM gear was in the larger style that was to become known by the rather unflattering term of 'Boatanchor'. The KW Vanguard and smaller (and rarer)  KW Valiant transmitters were paired with the KW76 (also very rare) and KW77 receivers.

As SSB began to dominate in the mid 60s KW downsized from the large KW Viceroy range of SSB transmitters to smaller separates that fitted into its KW2000 'G' Line..starting with the KW Vespa and KW201 and ending with the KW202 and KW204..sadly KW never got the hang of getting their searates to 'transceive' as a pair..something the competition had sorted pretty early on. 

KW 'One Sixty' TOPBAND AM TX - November 2017

Been after one of these for a few years. This came from an ex KW employee who decided to sell. Although it worked I quickly decided to replace all those nasty Hunts capacitors. Very little documentation although there is an article on the Web..the schematic around the VFO does not match my one though. Uses a TV PL81 valve in the PA with 21V heater winding on the mains transformer..Rowley must have got them cheap as it would have been more normal to use a 5763 or 6BW6. Power supply built in and full ' plate and screen modulation' from a 'push pull' audio stage. Its unclear when the 160 went out of production, it certainly ran alongside the KW2000s up until the mid 60s - although its look is distincly 1950s !. 

As we moved into the mid 60s the smaller, lighter and cheaper Codar AT5 became the Topband AM transmitter of choice for most UK hams - and has now achieved cult status !.  I was one of many that copied the AT5 design, its 'choke' modulation did away with the need for a heavy and expensive modulation  transformer..and with no bulky PSU built in, it was perfectly suited to mobile and portable operation.

G3ZPS 160m AM Station for GB8KW January 2018 - KW 62nd Anniversary


Ebay purchase delivered in  Jan 2016  - KW Vespa Transmitter (MK1) and its obviously re-built power supply, oh dear, what a mess. No way was I turning it on in this state - even more dangerous than when it came out of the factory in its odd cardboard cover, re build required. I changed caps, fixed awful dry joints, corroded fuse holders and put decent HV diodes in for the 750v HT..the ones in there did not look all that great.

After a 2 day total rebuild and test, the PSU was in good working order. Firing up the radio was met with ZERO output..not a milliwatt. Out with the scope and it soon became clear that the dreaded 455KHz Kokusai mechanical filter was as dead as a dodo, 455KHz carrier went in and nothing came out on the scope As a quick and dirty check I bypassed the filter with 1000pf...Bingo !!! Double Sideband and loads of drive. In the box of bits that came with my purchase there was 2 other filters one opened and one sealed.

On a whim I put the sealed one in the VESPA and it came to life again...super reports on 40m with a Shure 444. Later I found some resistors had gone high, and the curse of the KW Owners manual caught me out several times. Its one area where they really cut corners - the manuals are awful, child like drawings, schematics and charts with errors. Compare them to Swan, Drake and Collins and you will see what I mean.


Very clean KW201 Receiver from the 2016 Canvey Rally (Essex UK). Cheaper than eBay and promised as working on AM and with a good Mechanical Filter - but not good on SSB. This was a quick fault find quickly traced to an almost shorted coupling cap from the anode of the product detector to the grid of the Audio O/P valve.

That's why it worked on AM but not SSB. This receiver has a 3KHz filter which is too narrow for AM but means that SSB sounds great provided there are no adjacent stations - of course you can add the optional Q Multiplier - but I have never seen one for sale  BEWARE the old carbon composition resistors in these KW gear, in the KW201 2 failed within a few days of getting it going, they all go high, but some just go VERY high.. Although the 201 came out at the same time as the VESPA transmitter they cannot 'transceive' together and have to be manually netted together - this an another odd KW design decision, even the later KW202 and 204 'separates' had to be netted onto the same frequency and they were in production into the mid 70s.  Drake separates all allowed proper transceive operation.

The KW202 receiver is almost identical to the KW201 although it looks more like a KW2000B. The company re-used the same PCB for the 202 but had to add extra gangs to the VFO capacitor to account for 500KHz band segments, the Q multiplier was standard on the 202, but took up the space where the speaker was in the 201. And it gained that weird front end RF atteuuator (as in the KW2000E) which was called RF gain !. The IF gain on the 202 is the exact same control that was marked RF gain on the 201...!!!!

Below - Feb 2016, made a new slide rule dial for the KW201, using new perspex (cut to size and delivered off the internet) and an inkjet printed waterslide transfer. Took a bit of work in MS Draw to get the graphic the right size and looking good. But black is far better than the white lettering of the original. Its a strange dial anyway - good idea, but impossble to get better than 2KHz resolution (if your lucky and have good eyesight). I guess that was deemed good enough in 1967 - some stations I work now tell me my frequency to 5 decimal places !

The white lettering of the 201 dial on mine had faded and past efforts at clenaing it had only made things worse. I decided to buy a pre-cut blank piece of perspex and remake the dial in black. I used MSDraw and created a new one from scratch - I then printed it onto a waterslide transfer and applied it to the back of the perspex..looks ok and easier to read.

The Vespa and KW 201 are really only the TX and RX parts of the KW2000 transceivers and had similar limitations - only one filter bandwidth meant poor AM and CW performance, 200KHz band segments meant part coverage of 15 and 10m and did I say no transceive !