Re: solid state magnifier ---

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jan Florian Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

> I breadboarded the TL494 (NTE replacement chip is NTE1729) and associated 
> circuitry for it, the output looks great. I'm going to build the current 
> amplifying part tomorrow (push-pull with TIP3055's and
TIP42's......Richie is 
> using ZTX450's and ZTX550's but I'm hoping these xstrs will work since they 
> are NPN and PNP and have similar ratings......I'm hoping to "Americanize"
his 
> original design)

Just my $0.02: TIP42 and the other one are low frequency transistors with 
3 MHz unity gain, ZTX450&co have 50MHz. A cheap high-frequency 100MHz
version of such a transistor pair could be BC639 & BC640. (use
www.freetradezone-dot-com for parts search and comparison). They're faster and
need less base current, though might require one of those heat sink rings
(TO-92 case). I've had some trouble with slower transistors in TIP..
series and mosfet gate drive, but BC639 and BC640 performed just nice.

 - Jan

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