[R-390] OT: Transistor Amplifier Question

[Barry]

Happy to report that I got the 1060 boards refreshed with new caps (50pF included) and new silicon.  Sounds great - just like I remember.

Thanks for all the pointers.
Barry - N4BUQ

----- Original Message -----
> From: "Barry" <n4buq at knology.net>
> To: "R-390 Reflector" <r-390 at mailman.qth.net>
> Sent: Sunday, May 17, 2020 4:36:50 PM
> Subject: [R-390] OT: Transistor Amplifier Question
> 
> I apologize for asking an OT question but I'm not an EE and I don't find an
> answer to this with Google.
> 
> I'm refurbishing my Marantz 1060 stereo amplifier (bought it new in the
> mid-1970s).  On the preamp boards, some of the the transistors (BJTs) have a
> small value ceramic cap (50pF or less) connected directly between base and
> emitter.  Can someone tell me the purpose of these caps?  I'd presumed they
> might have been put there for spurious oscillation issues but I'm thinking
> that may not be the case.
> 
> From what I've read, a BJT has "natural" capacitance between the junctions so
> most schematics I see don't seem to need any additional capacitance.
> 
> Is it possible that those addressed some problems with the older BJTs and
> newer ones might not need that?
> 
> Thanks for any comments and, again, apologies for the OT post.
> 
> Thanks,
> Barry - N4BUQ
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