using new technology on old machines

Dave G4UGM dave.g4ugm at
Wed Jun 17 09:31:30 CDT 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Noel
> Chiappa
> Sent: 17 June 2015 15:08
> To: cctalk at
> Cc: jnc at
> 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
>     > 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
> 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

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