After looking at several regenerative radio circuits, I decided to build one. The goal is to end up with something that can listen at shortwave and 80/40/20 or maybe even 10 meters. Before venturing into HF, I decided to make an AM broadcast receiver, because its lower frequency and a much stronger signal: it's easier to tell when the thing is working. My question revolves around the tank circuit. It's an inductor and capacitor in parallel. Often, I see the output of the tank circuit connects to the base of a transistor, and the base has to be biased. To keep the base bias voltage from shorting through the inductor, a capacitor is placed between the tank and the base. It looks like this: (some one else's design) http://cool386.tripod.com/6tr/srrx.html I'm made a single transistor version, so I just have the 'core' circuit centered around Q2. L1, C3 and C4 make up the tank circuit, and choosing appropriate values for these for different bands is simple math. In fact, I have it working just fine in the AM broadcast band, just by using a much larger inductor and a larger capacitor. My question, is does the value of C5 contribute to the tank circuit? I originally thought not, it's just to keep the bias DC from shorting through the coil. I tried different large values, 1 uF, 10 uF, makes no difference. With values like 1uF, the DC is blocked, but any AC goes through just fine. But when I use smaller values (100 , 50, 20 pf etc) it seems to change the station I'm tuned to by a little bit My question is... why? It's not part of the tank, right? And why does smaller capacitors change it; if this cap is affecting tank resonance, then putting in something huge like 10uF should completely throw me off the band, but it seems the larger this value is, the less it matters. What's going on? My other question, is when I push this into oscillation (which is necessary to receive SSB), is the value of C5 going to affect the oscillation frequency? Is there an 'intelligent' way to choose what C5 is?