[R-390] Marantz

[Bill Guyger]

That is most likely the case. As someone else pointed out, the caps roll off high frequencies just for this reason. We still do the same today with the feedback loop around op-amps with a cap in parallel with the feedback resistor. When the reactance of the cap equals the resistance of the resistor, gain is down by 3dB and continues to roll off from there at 3dB / octave. Op-amps can go crazy under certain gain conditions. 

Bill AD5OL

Sent from my iPhone

> On May 18, 2020, at 9:04 AM, wb3fau55 at neo.rr.com wrote:
> 
> Guys, back at that time, a particular Marantz power amp would produce
> ultrasonic osc. This would case blowout of tweeters! Well maybe these
> 50pf caps were used as parasitic suppressors? Russ
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