Well, here we go again.... I was very interested in the Collpits test oscillator that featured in May 2011 RadCom Homebrew. After some deliberation I decided I would have a go at making one of them. This process has been rather traumatic!
Here is the schematic that I'm following:
It all looks rather simple - right? Well I built the basic oscillator based round the MPSH10, and then tried to find something similar to the listed 2SC495. I managed to destroy several transistors whilst doing this and eventually ended up using an MRF476 - which is total overkill but as I have them I figured this would be OK. Whilst destroying transistors (smoke, bad smell et cetera) I was unable to get the suggested 4V p-to-p output and could only really get about 2V p-to-p. I instantly blamed the amplifier section and just continued to blow up more alternative transistors.
Eventually I noticed a slight construction error in the basic oscillator - this corrected everything is working as expected. Here's the first oscillator and it's Cousin just beginning to take shape....
The output from the oscillator is very clean and the LPF in the design should have removed any harmonic content hence we see a very clean sinewave:
Just for some entertainment, here is my bench after constructing this simple little project:
What a mess!
And now, because I can, here is a closer shot of the construction of this little baby: