> -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Noel > Chiappa > Sent: 17 June 2015 15:08 > To: cctalk@classiccmp.org > Cc: j...@mercury.lcs.mit.edu > Subject: Re: using new technology on old machines > > > From: Dave G4UGM > > > I found it easier to think of it in DC terms. So the Cap charges > > through R5 + R3 and R9 + R8. > > As the Cap charges the voltage on the base of Q1 rises until it turns > > on, which then turns on Q2. > > At this point the cap is then charged (or discharged) in the reverse > > direction via Q2, D5 and R4 until Q1 turns off..... > > I'm clearly never going to be any good at analog stuff! ;-) Even with what > looks (on the surface) to be a wonderfully clear explanation of how the > circuit works, I still can't really grok how it operates! > > I mean, I can tell from the polarity on the cap that the collector of Q2 must be > at a higher voltage than the base of Q1, but I am utterly failing to understand > how the cap discharges through Q2. And as the cap charges (i.e. > the voltage across it increases), how does the voltage on the base of Q1 > increase - surely it must be decreasing (since it's tied to the negative side of > the cap, which is experiencing a voltage increase across itself)?
I think the cap is mildly abused. I believe that it is reverse charged. > > Like I said, I apparently don't have the gene for analog... :-) > > Noel