Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: RPMac on May 08, 2018, 11:30:22 AM

Title: Diode upgrade?
Post by: RPMac on May 08, 2018, 11:30:22 AM
Doing some work on my Parabee amps and wonder if there’s a recommended upgrade for the diodes?
Title: Re: Diode upgrade?
Post by: Doc B. on May 08, 2018, 11:47:31 AM
No, but we do offer a service of upgrading the filter caps to a series stack of two 350V rated caps to create a 700V cap for greater reliability.  Greater reliability meaning that the existing caps might only last ten years. It's a little tricky to do this modification, it requires some extra t-strips and can require re-positioning of other parts.
Title: Re: Diode upgrade?
Post by: RPMac on May 08, 2018, 01:01:25 PM
I’m replacing the power supply caps with CDE UNL 600V caps I have.
Was wondering if Hexfred or Schottky would be an improvement worth the trouble?
Thanks Doc
Title: Re: Diode upgrade?
Post by: Paul Joppa on May 08, 2018, 02:13:49 PM
Hexfreds are a variety of ultrafast/soft recovery silicon diodes. The original Parabee had UF4007 ultrafast soft recovery silicon diodes. Such diodes have a small, fast reverse recovery spike, which is further attenuated by the reverse recovery spike filter (RRSF) incorporated into the Parabee design. There is no real difference there.

Schottky diodes are even quieter; you might not need the RRSF - but you already have the RRSF, so what's the point? Again, you are very unlikely to hear any audible difference.

Cree does make a 1200v Schottky diode using silicon carbide, which has a bigger voltage margin than the usual 1000v diodes. But the fact that your ancient amps are still working suggests that the margin is already quite adequate. I suppose one might get a warm feeling from increasing the reliability margin.

On the other hand, we have seen a few amps whose PSU filter capacitors have failed in their second decade, which is why we offer the rebuild.