Using solid state rectifiers on Cary SLI80 Amplifier

Yes, jss, during the same conversation with Cary I asked about the ss diodes as a substitute for the 5U4’s. The response was similar to the bias question; they recommended against it for reasons of potential reliability and longevity compromise. Atmasphere, I agree that abandoning an idea simply because of one or several of its outcomes didn’t go completely as desired  can be a mistake. Also, even though I hadn’t thought of a noise factor, it’s possible that substantially  increased noise could result in my having written it off as strident. Also, although hearing aids have vastly improved my listening enjoyment, they can also play tricks with certain frequencies. Anyway, before I give up on the idea I will look into the HEXFRED suggestion although a bit more involved than a simple plugin. 

op - you have evidently talked to cary before to get biasing advice, why not ask them on the ss rectifier question?

i always treat the maker of x gear as the first port of call when it comes to how to use it, mod it, fix it etc etc... few will know better than the folks who designed it and built it

i haven’t read through the number of replies already (but i am responding to your op), so apologies if this particular reply is late and unnecessary at this point

The bottom line, though, after listening to many different pieces of music, other changes accompanying what sounded like improvements in clarity started surfacing. Upper mid and higher frequencies have become more sharp to shrill which doesn’t appeal to me.

@broadstone
When you make changes like this, you’re dealing with a set of compromises and you may have upset the apple cart. I find that good solid state rectifiers are better because you can support heavy bass passages better since the power supply sags less. But I’ve also seen rectifiers affect the sound since often solid state devices can make ’diode noise’ (which is actually caused by a resonance between the inductance of the power transformer and the capacitance in the junctions of the rectifiers; this can take a bit of work to snub the noise effectively) which can increase the IMD of the amp (resulting in harshness). In this regard, the HEXFRED rectifiers are some of the best we’ve heard but even they can have noise issues.

FWIW, when you google Yellow Jacket rectifier, all the hits are a bit sparse on information. This leads me to suspect that they employ silicon rectifiers, which are the mostly likely to have noise issues. So I would not write off solid state rectification until you’ve done more research. In effect, trying the Yellow Jackets, not liking them and then giving up on solid state rectifiers is akin to trying out a tube amplifier, finding you don’t like it and then give up on all tube amps. There’s a lot more than meets the eye with rectifiers!

Hoping not to run this into the ground I have a little more to say. The observations I reported in the last post remain correct to the extent that I’m meaningfully able to get the points across.  It’s obvious that everything is tighter and attack, especially for percussive sounds is quite noticeably sharper. The bottom line, though, after listening to many different pieces of music, other changes accompanying what sounded like improvements in clarity started surfacing. Upper mid and higher frequencies have become more sharp to shrill which doesn’t appeal to me. Some may prefer this sound, especially those experiencing upper frequency age related hearing loss (I’m one of those people but now wearing hearing aids). For me, those changes that I like are are not enough to trump the more laid back sound that I’ve become habituated to so, for the time being at least, I’ll stick to stock sound of the SLI80. Thanks to each of you who helped me get to this point. 

Ok, before considering any circuitry mods to accommodate rectification considerations, I wanted to know whether exchanging the tubes for ss would be worth pursuing in the first place. I plugged in the YJR Yellow Jackets, reset the bias to Cary’s 75mA recommendation and started listening.
The sound across all frequencies seemed tighter and with increased dynamics but the biggest improvement seems to be in timbre, especially listening to solo guitar music. Overall, the sound across the board just sounded more crisp (less tubelike?) similar to my favorite ss amp, the Ayre V3 which is very musical like the Cary but with a seemingly tighter overall presentation. So now I have some idea about the sound but I still have important decisions to make primarily regarding which setup I prefer listening to and whether I want to invest what’d be necessary to assure amplifier reliability. 

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?

Yes, to a certain degree. You don't have to worry about the tube rectifier going bad... For my part, I'd put the amp on the bench and see how bad things are when a set of HEXFREDs are installed. Measure the power supply voltages at idle, compare to the ratings of the caps (usually if you exceed 85% you're risking over-voltage under certain conditions).


One thing that can be problematic is the power supply is charged up long before the tubes are so there is no load. The no-load voltage is much higher! Some manufacturers (and I've no idea about Cary in this regard, I'm not calling them out), because a tube rectifier is used, will have lower voltage caps in the power supply as a result. But with a solid state rectifier, the caps will be in a no-load situation and so will be much higher than when the power tubes are warmed up.

If that no-load voltage is too high you can destroy the filter caps- and it won't just be the input caps to the power supply that are that high- **all** of the filter caps will be at this voltage until the tubes warm up. So you really want to be careful! It can be really upsetting when a filter cap blows its guts out.


If any of this sounds intimidating, good- if that's the case, you really might want to resist that urge to see what can be done. OTOH, if you feel like *perhaps* also replacing the filter caps maybe it won't be any problem. But at some point you might want to consider building the amp up from scratch.

As usual Atmasphere is spot on. I like the bass with SS rectification much more than tube in general. Check the voltage spec of your power supply caps and be sure they can handle the higher voltage per Ralph’s comments. New transformers spec’d to deliver the needed B+ voltage is certainly reasonable. Yes,  very costly. 

Atmasphere not atmosphere. Damned spelling correction feature. 

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. 

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.

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. 

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.

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

Harpoon, ALCM, Jadam, Slam ER, etc……

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

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: 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'd forget about using SS rectification and just change to an original 5AR4/GZ34 - not new production!

A good idea to increase filter cap life if they are not protected by a B+ delay relay is to replace the 5U4 with a vintage original 5AR4/GZ34. These have a slow warm up time and don't slam the filter caps like the 5U4 and other rectifiers. Plus the slow warm up lets the heaters  reach optimum temperature before B+ voltage. This is beneficial for power transformer life.

A SS rectifier will have less voltage drop and will cause a rise in the B+ voltage. The bias voltage will also be affected if it is not already regulated. Plus the fllter caps will be hit with a turn on voltage surge if there is not already a slow turn on relay in place. 

When he was still there, I discussed this topic a length with the former designer who made the initial design changes with the SLI-80 introducing ss rectification. I owned a SLI-80 Sig with many mods and before the rectification change was made official on that amp. I did like the presentation and bloom, and decided not to make the rectifier mod from tube to ss on mine. I instead sold that amp along with another high power Cary and moved to tube monos with ss rectification. While my new amps are a little faster with more bass control, sometimes I do miss the characteristics of tube rectification, often times finding myself looking to pick up another amp with it to swap in/out every once in a while. Grass may seem greener. A different sound, I like both for different reasons, fwiw.

Your willing to give stuff a shot, try a super rectifier


Oldhvymec I was going to suggest that but people on here will think I'm just a fanboy, but it would make a substantial difference in the bass if he ran a super rectifier with 3b22 or 866a tubes in it.

<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>

I'm a fan that's the reason I suggested it... What other people think and 5.00 dollars will get you a cup of coffee, right.. :-)

Me, I just like the weird $hit..:-).

Regards

I appreciate the comments and expressed concerns much of which have been part of my own thinking. And i realize that in the opinion of Cary staff they thought the voicing would would be a generalized most appropriate sound for the end users. The fact that they decided on solid state rectification, though, must be based on some reason of sonic improvement. In any case, it ultimately must result, good or bad, in change which can only be good or bad in the opinion of each individual. Most in this hobby seem, or at least claim, to  believe that listening tastes are so individual, no single component or combination of pieces can be the most appropriate for everyone. As much as I appreciate the Cary I’m not convinced that it fits me perfectly so if there is some way to achieve that goal it makes sense to me to find it. To the extent that I understand it, changing to ss rectifiers will not result in anything more than faster response and not an increase in sustained power increases to the various internal components, trying the ss rectifier seems like a relatively safe experiment. To avoid the initial surge, use of the Variac that I discussed earlier should accommodate that concern. I’m not an expert in any sense of the word so much of this argument is based on assumptions. That being said, I invite any comments that may keep me from doing something likely to be regretted. 

Your willing to give stuff a shot, try a super rectifier


Oldhvymec I was going to suggest that but people on here will think I'm just a fanboy, but it would make a substantial difference in the bass if he ran a super rectifier with 3b22 or 866a tubes in it.

IIRC, you can buy a solid state rectifier that simple plugs into the existing tube socket.  I forgot who makes it, but perhaps a google search will yield more info.

Your willing to give stuff a shot, try a super rectifier.

http://www.thebestamp.com/Accessories/Accessories.php

I have a pair of MC60s and I’m doing case swaps to 24k gold and blue anodized cap cans. I’m going to use super rectifiers on them..

I haven’t settled on exactly which ones yet..

Regards

Can you use 5ar4 rectifier tubes in the cary amp, they have less voltage drop than the 5U4G

Performing the surgery you contemplate, unless you are the Cary repair department, will significantly reduce the resale value of the amp.

I bought a new (tube rectified) SLI-80 a couple of years ago. I ordered all the factory mods available. These mods all help to give the unit a more *modern* tube sound. 

Try some new rectifier tubes. I don't necessarily mean vintage/NOS types. Many of those have the stereotypical (no pun intended) tubey, soft bass. 

After much rolling, I settled on Sophia Electric 274b tubes. Everything improved, including bass punch and clarity. 

Of course, you should do as you like. If it were me, and I wanted SS rectification, I'd ship it back to Cary for retrofitting. And maybe hexfreds, and Kimber silver wire, and Mundorf caps...

Good luck!

I would personally keep the tube rectification....   the amp was voiced that way.   Could be risky, IE costly.....   

One thing I have always  tried to do is stick with OEM parts and values whether it’s a tube amp or a car .    Bias, torque, whatever the spec may be I adhere to it.  It’s worked well 

Sounds like you are the R & D engineer for these mods. That means it's all on your shoulders. Good or bad, you'll be the crash test dummy. I'm not sure I would ever do anything to a good amp that wasn't a factory approved modification. But if you got the skills and the wallet to make significant mods, go ahead and have fun. You'll be an expert when you are done and that is worth something.