17 Jun
2015
17 Jun
'15
10:31 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Noel
Chiappa
Sent: 17 June 2015 15:08
To: cctalk at classiccmp.org
Cc: jnc at mercury.lcs.mit.edu
Subject: Re: using new technology on old machines
turns
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 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 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