Using solid state rectifiers on Cary SLI80 Amplifier

Heavy - as we used to say in the missile business ; Stuff that blows up….on purpose….

Harpoon, ALCM, Jadam, Slam ER, etc……

I'm running a super rectifier with Taylor 866a tubes to power my preamp, I know a preamp doesn't need this much juice, but it really made a big difference in the sound. My preamp sounded really good before the super rectifier, but now it's so much better. I want to get his bigger super rectifier that uses 872a tubes and has a diode/ tube switch.

Until this discussion I’d never heard the term “super rectifier” and I’ve been in this hobby off and on since 1959. My previous thinking about rectifiers has been that, because their function is not in the signal stream, their influence on sound personality/quality would be minimal and should be the last priority in pursuit of circuitry modifications to influence sound. Experimenting with biasing levels, though, has changed my mind. Although I’ve never considered myself to have the ability to discern subtle changes, adjustment of the Cary bias amperage from 75 to 90mA was significant even to me and I thought I’d found  a nice compromise between the Cary and several of my favorite ss amps. When Cary reps advised against the biasing increase or the substitution with ss rectifiers it was for reasons of shortened tube life, not degradation of sound quality. Anyway, I have a couple of ss rectifiers that I bought to replace the 5U4’s (as an experiment) but I’m a little afraid to try them based on warnings expressed here. I’m willing to accept some degree of shortened tube life associated with heavier biasing but my concerns about ss rectifiers damaging other components resulting in the need for expensive and time consuming repairs are what my worries are about. 

What I’ve learned from several sources is that the resulting instantaneous power to the tubes and power transformer could cause damage or, at least, blown fuses. Without adding circuit protection that delays the impact, does anyone have experience with this modification or insight otherwise.

@broadstone First, the inrush current will not be a threat to the power transformer so you can cross that off the list of concerns. Its unlikely you'll be blowing fuses too.

The concerns are these: the power transformer was designed to make the right DC voltage when used with a tube rectifier. When you go solid state the voltage drop will be less (and you get better power supply regulation since there is less voltage sag when the amp is at higher power). The problem is that voltage might be more than the tubes, filter caps and transformers might be able to handle. The primary of the power transformer won't care much since the filament load of the rectifier was removed. So there's that.

But the real issue IMO is the extra B+. There are solid state rectifiers packs that are meant to replace tube rectifiers. Some of these have a voltage drop to mimic a tube rectifier, but they don't act the same way. I think using solid state rectifiers is a good idea since the voltage drop that tube rectifiers have contribute to distortion in the amp and extra distortion is never good. If you really want to do this right the way to do it is get the newer power transformer and replace your old one so you get the right operating voltages.

I know that's an expensive solution but if you want to do it right, that's the best way to go about it.

Atmosphere, over the years I’ve learned much from your posts and I appreciate this response which I think I mostly understand. Anyway, because I’ve already bought them I’m going to try the ss rectifiers simply out of curiosity. I have one question, though; for those ss diodes that are designed to mimic tubes, if part of that feature is to more slowly ramp up the application of power, will that not also affect these diodes’ reaction speed overall and negate the reason for their substitution in the first place? Im probably overthinking this and a bit over my head technically but this all started when I went back to using the relatively low sensitivity Martin Logan CLS2 speakers and was looking for a bit more dynamics still keeping the Cary in the system.