And how it differs from the “A” model.
In my last three posts I have described in detail my restoration of an early ca. 1951 Kenwood Chef A700 mixer. The first Chefs, up until the A700 “D” model in the late 1950s, are all much the same in design, albeit with several small changes along the way. The D model has more significant changes, including a new body shape. This is reflected in Kenwood’s labeling of all pre-D model Chefs as simply an “A700” model on the machine itself (and in the service manual), whereas the later D model was labelled as an “A700-D”. Despite the seemingly continuous small changes to the first pre-D Chefs, at some point someone decided to divide them into two variants – the “A” and the “B”. The website for Kenwood Chef Restore, a commercial restoration service in the UK, states that the main external feature that identifies a B model is a change in the motor air vent design from the single slot of the first machines, to two smaller slots as shown in the picture below.
Another feature introduced with the B model (or at some time during B model production) was the option to have plastic parts in a colour other than black. I’ve seen photos of later D models with different plastic colours (green, yellow, blue, red etc.), but I’ve only seen B models with black or red plastic. I thought that maybe these were the only B colours offered, but recently I came across an image of an old Kenwood advertisement showing a B model and headlined; “The Kenwood Chef, Now in COLOUR!” (curiously, the machine illustrated has a black speed knob – see update below for possible explanation). The advert helpfully lists the colours available as: Signal Red, Apple Green, Pastel Blue, Rose Pink, Jasmine Yellow, Dove Grey and, Cream and White.
UPDATE: Since writing this I have found an example of a B model A700 with original pale green body paint and black plastic parts. I now think that the advert mentioned above was referring to the actual body colours, not the plastic colours.
Not long after restoring the A700-A model described in my previous posts, I saw a fine example of a white B model with red plastic parts for sale on a local auction site. I couldn’t resist, and managed to buy it at a bargain price.
And now I’ve finished restoring my lovely red A700-B. I found a few differences to the earlier model, particularly in the wiring, so I though I’d write this post, highlighting the differences for those who are interested.
The only external differences, compared to my early A model mixer, are the change in the design of the motor vent holes as mentioned above, and the use of a rubber grommet where the power cable exits the body. My A has no grommet, but I note that later A models did have a grommet. Otherwise the body shape is identical, and the external parts are the same and interchangeable with the A model (the speed knob, plastic parts, screws, bowls, bowl springs, attachments, feet etc.). In fact in the original Kenwood service manual there is only an “A700” model, with one parts diagram covering all A700s up until the A700-D. Another difference to my particular A machine is the logo. My A has an early “Kenwood” only style logo, whereas this B has the “Kenwood Chef” logo. This meant that I needed a new logo for the restoration, so once again I photographed the logo, drew it up in Adobe Illustrator, and got the good folk at Grizzly Decals to reproduce it in black glossy outdoor vinyl (hint: make sure you tell them not to scale your artwork – assuming you’ve drawn it at exactly the right size). Once again, the result was awesome.
Gear Train and Planetary Hub
Again, there are no significant differences in the gear train. There was, however, one difference in the brass bushing for the planetary hub drive shaft. My A machine has a fixed brass bearing, whereas this B has an adjustable screw-in brass bushing. To remove, first remove the planetary drive shaft and gear, then remove the two thin brass nuts which lock the bearing. Finally, unscrew the bearing out through the gearbox.
There is a note below one of the photos below about adjusting this bushing on re-assembly.
Motor and Electrics
The motor was essentially the same as my A model, as were the fan and wishbone assembly, the hinged governor switch, and the design of the metal shroud. The wiring and electrical components were different however. Differences are listed below:
Two inductors have been added to the circuit by mounting them under the small paxolin terminal board. The inductance values were not given on the parts, but kits sold online use 22uH ferrite-core inductors. These are available from RS components (stock number 213-1881), which is where I got my replacements.
The circuit has a 4.7nF line-to-ground suppression capacitor as well as a 0.1uF across-the-line suppression capacitor (my A model had a 50nF across-the-line capacitor only). When replacing these, make sure that the 0.1uF cap is X2 supression class, and the 4.7nF cap is Y2 supression class.
The radial snubber capacitor for the governor switch has a value of 0.22uF, up from 0.1uF in my A model. I actually found a direct replacement polyprop radial snubber capacitor to mount on the governor switch. This part is RS stock number 871-7034.
The resistor in series with the snubber capacitor is implemented as a 5.4 ohm tap of the external wire-wound resistor, rather than a discrete resistor soldered to the capacitor as in my A model.
Here is the wiring diagram:
Once again, I designed and etched a small circuit board for the inductors and suppression capacitors. This time I reused the external wire-wound resistor, which was in good condition. This saved me having to find room for a 5.4 ohm resistor. Also, I intend to put this mixer to regular use. The smaller ceramic encased resistor I used in the A has not been sufficiently tested under load for me to be confident enough to use it here. It’s an option if the original resistor ever fails.
So those are the main differences. To finish I’ll leave you with some images of the restoration. Thanks for reading.
UPDATE: Motor Surging Problem Fixed.
When I first assembled and tested my restored motor, it ran perfectly. I then discovered that, despite being careful, I had somehow ended up with the motor slightly twisted in the shroud and had to pull it all apart again (see part 2 of my previous post for info on motor orientation). When I tested it again after putting it back together I found that it now surged at low speed, and briefly over-revved each time the speed was increased. I pulled it apart again, but was unable to determine the cause, so I just put the mixer together as it was. This bugged me, however, as I really wanted the mixer to work perfectly. So I took the motor back out of the mixer and pulled it apart again! This time I found the problem. Actually it was my wife who made the critical observation: on the wishbone assembly, the ends of the copper spring arms that fit through the slots in the aluminium wishbone (officially called the “yoke” in the service manual) were bent at different angles. The result was, that as the spring arms moved outwards with increasing motor speed, one side of the yoke would start to move down before the other. This caused the tip of the yoke to tilt and jam on the motor shaft until the motor sped up sufficiently to overcome the jam. Thus the surging and over-speeding.
You can actually detect this problem without having to run the motor. With the mechanism installed on the motor shaft, try and move the wishbone backwards and forwards (the bit being held in the photo above). You should be able to move it a small amount back and forth easily, without it sticking on the motor shaft. If it slides freely on the shaft it should function properly. If it sticks then suddenly gives way, you will most likely encounter the problem I had.