BWD (Beasley, Wingate and Dewey) Model 509B Oscilloscope

This site contains a download .pdf for the B.W.D. Model 509B 10MHz single trace Australian Oscilloscope. I have been researching B.W.D. and the products they made, particularly the 1970's and '80's Oscilloscopes.

It seems that when they made a new model, they gave it a model number...let's say, "509".  As they improved the design of that model, (generally by removing thermionic valves and replacing them with discrete semiconductors) they added a subsequent Roman letter to the base model number, so Model 509 "evolved" into "Model 509A" and then later, "Model 509B" etc.

Each revision is thus somewhat different from its previous lettered predecessor and thus the circuit diagrams are quite different also.  The general principles and layout of the circuits are still similar however and if one gets to see a number of different lettered versions of the same base model number side by side the developmental trend was quite obvious. John Beasley, the "B" in BWD designed most of the 70's and '80's scopes and his methodology is quite apparent.

This is what I know about the 509 series...

The 509 (with no Roman Letters after the number) was the first model in the line and dated from about 1969-70. It contained a number of thermionic valves/vacuum tubes, viz, three 6ES8's, (ECC189's for Europeans) and two 6BL8's, (ECF80's). One of the 6ES8's did the differential front end of the Y-Amp and the other two were the differential output stages for the X and Y amps driving the deflection plates of the tube. The two 6BL8's were possibly in the timebase but I cannot currently be 100% certain about that as I have only ever seen pictures but not the actual circuit diagram.

The 509A eliminated the two 6BL8's but retained the three 6ES8's. I have seen the circuit diagram of this model.

The 509B eliminated ALL the thermionic valves, replacing the front end 6ES8 with two MPF106 j-FET's and the other two Output stage 6ES8's with pairs of BF337 fast bipolar transistors. This is the circuit diagram that appears on this site. I have repaired and restored this model and are thus quite familliar with it.

There is the possibly that models 509C and D exist but, so far I cannot prove it.

The Model 539 was basically the dual channel version. I own or have seen and critically compared the 539A, 539C, 539D and the 820, (effectively the "539E" as they changed all 1980's model numbers to start with an "8" in the new decade) and have seen online pictures of the 539B. I have never seen any evidence of a 539 (with no subsequent letters), but it makes sense that it exists particularly when compared to the 509 series. 
  None of the 539 series from the "A" onwards contain any thermionic valves apart from the tube but it is possible that the 539 (with no Roman letter after the number) does and it is most likely to be a few 6ES8/6DJ8's.

Earlier (all thermionic valve) models from the 1960's indicated that 6ES8's (ECC189's) and 6DJ8's, (ECC188's) could be used interchangeably so this is probably true for the 509 and 509A too. 

BWD were always "pressed for money" and made their equipment with the most commonly available parts. (They strove for the best quality and performance from the most common parts). They also had this Australian philosophy that any piece of BWD equipment could be fixed "out on a Cattle station behind the branding pens with a piece of fencing wire a pair of Bull-Nosed pliers!" This is possibly why so many pieces of BWD gear survive well into the second decade of the third millenium.

In the 1960's the 6ES8 was used as the cascode VHF amplifier in the front ends of monochrome T.V. tuners and the 6BL8 was used as the mixer-oscillator in the same tuners and in other parts of the T.V. set...hence why they were so common in the BWD gear of the time too.