Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Not so much a prototyping "system", but in the early days of radio it was usual to mount the components on a wooden board similar to that used as a base for cutting bread.Doesnt the term breaboard come from a tube prototype system?
If I can get it to work reliably, and with a reasonably small parts count, then the plan is to use tubes in the final build.
Pictures are attached. A couple of scope traces are included. In the first one, the scope shows the 38 kHz crystal oscillator waveform in the lower trace, and the 10.857 (divide by 3.5) blocking oscillator output waveform. Note that dividing by a non-integer number is not recommended, because it requires very fine and critical adjustment of the RC network. Integer division is fairly non-critical.
View attachment 111448
In the next photo, the scope shows the blocking oscillator trace again (upper), and this time the lower trace is the output of the JK flip-flop, which is triggered from the blocking oscillator output, and is running at half the blocking oscillator frequency. If the J and K inputs are tied to logic 1, or left unconnected as they are in this case, then the output alternates state on each trigger pulse.
View attachment 111447
Below are closeups of the breadboarded circuit. The upper breadboard is the crystal oscillator (left side) and blocking oscillator (right side). The 6U8 tube is lying on its side above the breadboard. The lower breadboard is the JK flip-flop, and the rectifier/filter for the -100V bias supply. The bias supply transformer is powered from a variac (grey box on the right) so that I can adjust the bias voltage accurately. The main power supply is the grey box in the upper part of the photo. It supplies both +150V and 6.3VAC for the filaments.
View attachment 111445 View attachment 111446
The mains power here is quite stable. So, I'm hoping that I won't have to add any special circuitry to stabilize the power supplies. But if I do, I'd probably look at a tube type regulator. It would be cheating to use a solid state regulator when everything else is built with tubes.