Steve Anderson wrote:The values of the components and the output frequencies listed within the 4046 diagram above agree fairly well with the Philips datasheet.
As it shows a 9-12V supply it's a HEF4046 (Philips) or a CD4046 (Motorola & Texas), so your examples should be OK.
I say 'fairly well' as there is an immense spread amongst these devices. This is down to the Silicon process used to fabricate the chips, it's more suited to logic circuits rather than linear ones - which is what the VCO is - linear. For the same reason these devices also have a chronic sensitivity to the supply voltage, it must be regulated otherwise the frequency will be all over the place. Note that pin 15 has a 7.5V Zener for precisely this reason. The HC version doesn't have or need this, a third phase comparator output is present instead.
But if you've got the unijunction version going I would continue with it.
Steve A.
Thanks Steve its good to know the 4046 i have will work that will be my experimental go a VCO ,i like to get the hang of these things to see how they should work .
Well i did end up dropping by Jaycar store today and got the ujt its in the circuit now and i know that now works it has a better or wider frequency range than the bc547 circuit version from the 73 magazine its pretty much just a little over or lower than the needed range ,This unijuction oscillator frequency range is about 600hz to over 10khz .
I will do a full test on the rest of the circuit when i am off work later this week .
I am putting together a simple tv bar generator for testing the sstv VCO circuits before i start playing with a head amp with it .