valve simulator - for good old fashioned radio noise

for good old fashioned radio noise Nostalgia is becoming ever more of a "big business". This is understandable as we all have a tendency to remember "the good old days" when life was simpler, less complicated, and everybody was happy. In reality, of course, it was quite different but we often prefer to let our minds play tricks on us so we only remember the good things. Part of the nostalgia for many electronic hobbyists has to be the original valve radios. They were a breed apart, with the way they looked and the sounds they made, and it was impossible not to be taken in by their magic. Many at- tics still hide these radios, which no longer work, so we thought it would be interesting to fit a transistor radio into one of these old cases and add a bit of "magic" of our own. Then your modern radio is guaranteed to make genuine "antique" noises and it even takes a while to warm up just like valves always do. The circuit is based on two oper- ational transconductance amplifiers (OTA)...