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David G4EBT · 24th Sep 2018, 8:50 pm

At Post #8 of the thread below I added a pic of a PCB I’d etched for a sawtooth generator as an add-on to the Radio Bygones Wobbulator.

https://www.vintage-radio.net/forum/...d.php?t=149574

At Post #10 Terry, VK5TM asked what magazine the article had been published in and I replied that it was a design forwarded to me by forum member ‘Colin’ (Colin Armstrong). I said that though Colin isn’t very active on the forum these days, I’d e-mail him to ask if he was content for me to post the circuit and PCB layout on the forum. I’m pleased to say that Colin has responded to say that he’s quite happy for me to do that, so I’ve appended the circuit below, along with the PCB artwork, both positive and negative, the component overlay and a scope trace of the completed project. (The size of the PCB is 8cms wide x 7cms tall).

To reiterate why Colin designed the sawtooth generator, he hadn't wanted to use his 'scope timebase, so he built the generator into the wobbulator and redesigned the front panel to add a timebase control. To quote Colin at the time: "The circuit for this used a couple of discreet transistors, a 555 timer IC and two Op Amps from a Quad LM324. I used the other two spare Op Amps in this as high impedance buffers for the output of the wobbulator. They also serve to invert the output so the ‘peak’ on the scope is up rather than down".

When I buiult mine, it refused to work with a 555 and Colin discovered that some 555s don’t readily oscillate, but by replacing the 555 with the CMOS version – 7555 it solved the problem. The 78L12 12V regulator was included on the board as it is fed from the 2 x PP3 batteries that feed the RB Wobbulator into which the sawtooth generator was installed.

Though on the PCB layout the frequency adjustment pot is a miniature preset one, as stated above, Colin modified the RB Wobbulator front panel layout to included a timebase control on the front panel rather than as a pre-set on the PCB, so three terminal pins were soldered to the PCB in place of the pre-set pot, with leads to the timebase pot on the front panel.

Pic1 - Circuit.
Pic2 - Positive UV mask
Pic3 - Negative UV mask
Pic 4 - Component overlay
Pic 4 - scope trace of waveform.

(I should perhaps add that I built this project back in 2013, though for clarity, I've just re-drawn the circuit as it was originally a hand-drawn sketch).

Hope that’s of interest – at least to Terry, who’d asked for more details.

Colin tells me that though he has ‘officially’ retired, he’s busier than ever nowadays, offering a service to repair, restore, upgrade and sell classic car radios:

http://agentaaudio.co.uk/index.html

24th Sep 2018, 8:50 pm	#1
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,766	'Sawtooth Generator' project At Post #8 of the thread below I added a pic of a PCB I’d etched for a sawtooth generator as an add-on to the Radio Bygones Wobbulator. https://www.vintage-radio.net/forum/...d.php?t=149574 At Post #10 Terry, VK5TM asked what magazine the article had been published in and I replied that it was a design forwarded to me by forum member ‘Colin’ (Colin Armstrong). I said that though Colin isn’t very active on the forum these days, I’d e-mail him to ask if he was content for me to post the circuit and PCB layout on the forum. I’m pleased to say that Colin has responded to say that he’s quite happy for me to do that, so I’ve appended the circuit below, along with the PCB artwork, both positive and negative, the component overlay and a scope trace of the completed project. (The size of the PCB is 8cms wide x 7cms tall). To reiterate why Colin designed the sawtooth generator, he hadn't wanted to use his 'scope timebase, so he built the generator into the wobbulator and redesigned the front panel to add a timebase control. To quote Colin at the time: "The circuit for this used a couple of discreet transistors, a 555 timer IC and two Op Amps from a Quad LM324. I used the other two spare Op Amps in this as high impedance buffers for the output of the wobbulator. They also serve to invert the output so the ‘peak’ on the scope is up rather than down". When I buiult mine, it refused to work with a 555 and Colin discovered that some 555s don’t readily oscillate, but by replacing the 555 with the CMOS version – 7555 it solved the problem. The 78L12 12V regulator was included on the board as it is fed from the 2 x PP3 batteries that feed the RB Wobbulator into which the sawtooth generator was installed. Though on the PCB layout the frequency adjustment pot is a miniature preset one, as stated above, Colin modified the RB Wobbulator front panel layout to included a timebase control on the front panel rather than as a pre-set on the PCB, so three terminal pins were soldered to the PCB in place of the pre-set pot, with leads to the timebase pot on the front panel. Pic1 - Circuit. Pic2 - Positive UV mask Pic3 - Negative UV mask Pic 4 - Component overlay Pic 4 - scope trace of waveform. (I should perhaps add that I built this project back in 2013, though for clarity, I've just re-drawn the circuit as it was originally a hand-drawn sketch). Hope that’s of interest – at least to Terry, who’d asked for more details. Colin tells me that though he has ‘officially’ retired, he’s busier than ever nowadays, offering a service to repair, restore, upgrade and sell classic car radios: http://agentaaudio.co.uk/index.html Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.