That will appeal to people who just want their scope working and don't get a big kick out of re-engineering it as I do. I think my hobby niche is becoming "retrofit engineering".
Dave Wise
________________________________________
From:
[email protected] <
[email protected]> on behalf of Bill Perkins via groups.io <sales@...>
Sent: Tuesday, September 15, 2020 11:59 AM
To:
[email protected]Subject: Re: [TekScopes] 547 Repair - how do you locate where parts are located on ceramic strips?
There's a slew of what look to be real deal NOS 2N2207s on eBay, here:
Best,
Bill
For Q173 and Q373, the critical attributes are Cob and BVcbo. Q184 same except Cob is not top priority.
My best results were BC556 and KSA992. Both required extra speedup capacitance. MPSA56 was okay but it needed more C. I don't have a BC640, but it probably does too since Cob is 9pF typical vs 6pF max. I would try 330pF. Be sure you know the pinout of whatever you try, they're all different.
As far as I can tell, no modern transistor equals the 2N2207 in this application.
Here's the conclusion from my original post.
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RECOMMENDED (demonstrated working)
BC556 + 220pF
KSA992 + 220pF
MPSA56 + 470pF
NOT RECOMMENDED (insufficient breakdown voltage)
2N3906
2N5086
2N5087
KSA1015
PN4133
NOT RECOMMENDED (slow even with cap)
2N5401
BC638
KSA708
GOOD BUT HARD TO GET (obsolete)
AF118
2N2207
MPSH55
NOT TESTED (because I don't have)
2N3486
2N3505
2N3799
2N3962
BC640
KSA733 probably no better than KSA992
PN3645
PN4249
OTHER 2N2207 USAGE
The 547 has 2N2207 in six places: Q173/Q184/Q373/Q424/Q554/Q564. I believe that all
of these can be replaced by BC556 or KSA992, subject to enlarging C170/C370.
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Regards,
Dave Wise
