piclist 2001\06\27\132208a >
Thread: Transistor replacement
www.piclist.com/techref/index.htm?key=transistor+replacement
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face BY : Chris Carr email (remove spam text)



As there is one transistor that is still operational, why not remove it and
measure its characteristics. Then substitute a pair of modern transistors
with similar characteristics.
My apologies if this has already been suggested, I have only been half
following the thread.

Chris Carr

> "Alan B. Pearce" schrieb:
>
> > >Yes, this is possible. Most probably they were selected in pairs of
equal
> > >beta, remember that we are talkind about DC-coupled diff amps here.
> > >Greets
> > >Jochen Feldhaar DH6FAZ
> >
> > Granted, but by the time you get to the output stage, I suspect that
these
> > are really only level shifting to drive the deflection plates, and
> > transistor beta spreads are designed out by careful feedback
arrangements.
> > In view of it operating at a voltage greater than the manufacturers Vce
> > rating I would think that this would be the primary selection criteria,
with
> > possibly a minimal test to remove outliers in the beta spread.
> >
>
> Hello Alan,
> the part about the feedback is not correct IMHO, there is no feedback from
the
> deflection plates to earlier stages. The trick is done by current sourcing
and
> AC compensation. The HAMEG 1007 featured a trigger view showing the actual
> trigger point out of the peak rectifier, and we were joking for months
before it
> started to give accurate results. Also the paired beta was necessary in
the X
{Quote hidden}

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