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Using solid state rectifiers on Cary SLI80 Amplifier

One might wonder why experimenting with such a high performing amplifier as this SLI80 Signature is but I would like to try this to see if doing so will tighten bass and/or percussive sounds from things like drums and piano. I’ve tried raising the bias above the Cary recommended 75mA and the sonic difference was significant but, because the higher resulting voltages to the tubes would be continuous while operating, Cary recommended against it primarily because of predicted shortened tube life. I’ve taken their advice and adjusted the amperage down to 80 from the 90mA that I was trying. Now, based partly on Cary’s having switched to solid state rectification in their newer amps, I thought it made sense to try it on this older amp and need advice concerning exchanging the tube diodes with solid state replacements. 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. I do have a variac to lessen the initial impact of this experiment if I decide to do so.  Thank you. 
broadstone
invalid
1,378 posts
 
oldhvymec: the 866 is a mercury half-wave rectifier tube. It must be warmed up first before any B+ voltage is applied! Otherwise it can explode! Anyway two are needed for full-wsve rectification.


I run two 866a's in my super rectifier, it has a standby switch for preheating. They do not explode, they can arc over if not preheated for about 1 minute if they have been in circuit,  and if they haven't been in circuit they need about 30 minutes warm up.
oldhvymec
5,101 posts
 
Thanks fellas, BUT I like stuff that blows up..:-)

Really what do you think of a super rectifier in my MC60s it would take a pair one for each and twin valves in each?

They still have tube rectifiers.

They run 5U4 GEs all Mac factory Valves, they haven’t been powered up in 25 years, a rebuild and super rectifiers?

What about a SR in the OPs unit? It’s Gotta’ be the Cats Meow?

I have a few 866a Pinnacles some where. A WE amp I had used them..

So OP you ever think of using a SR? Do somethin’ weird.. :-)

Regards
tomic601's avatar
tomic601
13,743 posts
 
Heavy - as we used to say in the missile business ; Stuff that blows up….on purpose….

Harpoon, ALCM, Jadam, Slam ER, etc……
invalid
1,378 posts
 
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.
broadstone's avatar
broadstone OP
310 posts
 
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. 
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