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Do rectifier tubes matter?


Schu

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Rectifier tubes do matter. If you remove the rectifier tube, the equipment will no longer work.:emotion-14:

 

There should be no audible difference between rectifier tubes of the same type, if they are in good shape. Audible and measurable differences between rectifiers tells me they are used, maybe half used up.

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20 hours ago, Don Richard said:

Rectifier tubes do matter. If you remove the rectifier tube, the equipment will no longer work.:emotion-14:

 

There should be no audible difference between rectifier tubes of the same type, if they are in good shape. Audible and measurable differences between rectifiers tells me they are used, maybe half used up.

 

  Funny your first sentence above is how I almost first posted in this thread :)

  Thing is even with well used rectifiers very few types show much voltage or current delivery diminishing until they are pretty much worn out. Most tubes are like that they test and work like new for about 90% of there life.. The last 10% the test results and performance drops like a rock. 

 

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  • 9 months later...

rectifers do make a difference in the sound. they shouldn't but they do.

my mp dac2 has a switch to allow me to use 5 or 6 watt rectifers. I went to a guy in town & spent about $80 for 6 different ones, sylvania, rca, rogers, marconni. short, tall, fat, skinny. each has a different quality to the bottom end (different degrees of loose to tight) 

the ones I liked in my system I took to a friends place who has the same dac & the sound was totally different. 

different amps, speakers, room size...they'll all make a difference. buy a bunch & experiment, that's the fun of tube rolling. the ones you don't like, resell or trade with a friend for something different.

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The rectifier issue aside -- though I'll mention that in addition to varying increases or decreases in what they can offer to the high voltage rail (aka B+) of a given circuit, one MUST give consideration if, for example, one starts experimenting with some of the different 5V rectifiers available.  Swapping one brand of 5Y3 for another, if that's what the circuit was designed around, is fine because one is not changing such things as filament current draw (which is an important consideration) and capacitor input to filter values (which is not the same for all rectifiers; and, if not considered, can greatly reduce valve rectifier life.  That said, there are quite a few people, myself included, that, as Bruce mentioned above, DO in fact detect sonic differences by intentionally using a rectifier that offers a bit of 'sag', or the opposite of that, greater 'stiffness' with regard to plate voltages supplied to input/driver, and output stages.

 

Moreover, I'm glad to see reports from those happily using and enjoying active preampfification.  We all choose personal paths to music enjoyment, and, without exception, that's a good thing -- as is respecting different tastes, options, personal choices....

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Since this is a preamplifier we are discussing there won't be any sag due to the relatively constant load current. Usually output stages that go into class B and have unregulated supplies will get some sag and natural compression. Changing from one type to another, like 5Y3 to a 5AR4 can change the operating points by increasing or lowering the rail voltage.

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  • 2 weeks later...
On 9/2/2016 at 9:26 PM, mike stehr said:

6X4s are cheap...maybe try a Mullard...it will last quite awhile provided it's a good tube. OTOH, rolling different brands of the same type of rectifier with various amounts of wear will effect the B+ voltage.

That difference in B+ is what possibly one hears as a change in sound.

Everything will affect the sound, theoretically.  I'm thinking Mike's observation about the rectifier is spot on. Now tube rectification versus diode type rectification could produce a more nuanced argument.  I've heard a bunch both ways, and Maynard's a big believer in diodes, so I'm conflicted.  However can you even talk about tube rectification without  a discussion about chokes?

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On 7/2/2017 at 7:49 PM, thebes said:

I've heard a bunch both ways, and Maynard's a big believer in diodes, so I'm conflicted.  However can you even talk about tube rectification without  a discussion about chokes?

There's little reason to use a tube rectifier given the availability of high quality solid state alternatives.  Tube types are limited by fairly low peak current capability which is why the first filter cap has to be relatively low in value.  Unfortunately, this results in a large amount of ripple (AC riding on the DC) which has to be dealt with.  A choke is the only reasonable way to get rid of it in a power amp or other device which draws moderate or high amounts of current (there's also the issue of regulation which is a subject for a different discussion).  However, in low/constant current devices like preamps it's not much of an issue and a resistor will often work just fine instead of a choke.  In any case, when designing new equipment, I would rather use a couple of 50 cent diodes (which should last forever) in combination with a high value cap, than add another tube to draw filament current and add additional heat.

 

Maynard  

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Tube fanatic

 

Whether the reasons one designer chooses a valve rectifier over SS diode is surely, arguably, a matter of personal preference, and what he or she believes to be the advantage of one over the other in his or her specific circuit.  We can't, or rather, should probably not, speak in terms of absolutes, because what either of us is expressing is our own personal bias.  There are a number of very highly regarded tube preamplifiers that in fact favor valve rectification, at least for plate voltages, over a couple IN40007s, for example.  Prima Luna designs and builds very good tube equipment, and their preamps, with which I have long-term personal experience, are really superb performers -- in my opinion.  They not only use tube rectifiers, but one per channel in dual mono power supplies.  Mine is also, for all intents and purposes, essentially dead-quiet in terms of residual noise.  From many years of experience, I whole-heartedly disagree with the idea that active preamps are nothing more than noise and distortion boxes.  But that doesn't make me correct in a global sense.  It makes me correct in terms of my own experience, as well as what I know others have expressed in terms of what they perceived as improved performance.

 

But sure, one could argue that a couple of tremendously less expensive SS diodes would do just fine (and I have taken that route myself in the past)  -- and someone else might feel very strongly about his or her reasons for using, for example, a 5AR4 into a choke input to filter vs a simple resistor (also MUCH less expensive) over a heavy chunk of iron.

 

And you're also correct that the valve rectifier will also need a dedicated filament supply, which means that a designer must account (as most designers do) for the extra current draw when choosing power transformers, or even a separate, dedicated filament transformer with a single, 5 volt secondary (in the case of a 5 volt rectifier).  But that fact alone, in my opinion, does not by itself suggest faulty power supply design.  If it happens to be a less than desirable option for someone, that person has every right to take a different course.  IMHO.

Edited by erik2A3
typo correction
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I always learn so much here.  Both Maynard's and Eric's comments make perfect sense to me although they diverge in their conclusions.  I can also certainly understand that for most tubed preamps a massive power supply is not needed.  And heat is always a factor in design longevity because it can weaken components over time. 

 

People using a choke regulated power supply may simply be following in  the footsteps of their tube amp building predecessors, don't car about expense because a tubed power supply aids in marketing their product as high-end, or believe that this approach yields real sonic benefits. 

 

Hard for me to determine, but interesting food for thought.

 

I thank you both for your detailed replies.

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Engineers have decisions to make and there are always tradeoffs.

 

Benefits of Valve rectification is no switch noise which is found in SS diodes and most importantly is with inderectly heated valves you will get a controlled soft start. The latter is very desirable and removes the need for soft start circuits. The switch noise found with SS diodes can be mitigated via snubbers  and or the use of Schottky diodes.  The negative aspect of using valve rectifiers is the limited repetitive peak forward current rating, this limits the amount of capacitance and load that can be used.  Using a choke is not an en vogue, it is necessary as Maynard pointed out. With a full wave rectifier you are trying to filter out 120Hz, you can view the filter as a potential divider. The choke or the resistor is the serial element and the capacitor is the shunt element in the filter, like a potential divider you want the serial element large and shunt element small;

 

Potential_Divider.gif

 

 

Vout = Vin * ( R2 / R1 + R2 )

 

 

The reactance of say 40uF at 120Hz is 33 ohms.

 

To simplifiy I am going to ignore phase but this will illustrate my point just fine. To get any sort of filtering we would want to make the serial element (R1) much larger than the shunt (R2), at least 10x but the larger the better. Say we use a 330 ohm resistor;

 

33 / 363 = .09 

 

We are left with 9% of the ripple  so we either need to make R1 larger or R2 smaller, or both. But if we have say 20mA of load current and we want to increase R1 to 1k we will end up losing 20 volts of DC, it gets worse the more we increase R1 value. This wastes energy into heat across the resistor which is bad. The best way of doing this is to use a Choke which has a high impedance to 120Hz but passes DC, the only loss is the DC resistance in the winding. So let's use a 10H choke with a DC resistance of 150 ohms. The choke will have an impedance of 7.5k at 120Hz but we will only lose .02 * 150 = 3 volts across it. Lets see how much we reduce the ripple;

 

33 / ( 7500 + 33 ) = .0044

 

We are now left with .44% of the ripple and we only lost 3 volts DC across the choke.

 

With SS rectifiers we can have much larger capacitance. Let's use 1000uF, this is 1.3 ohms at 120Hz. With a 330 ohm resistor we get .39% of the ripple and only lose 6vdc. 

 

So you can see with SS diodes you can use large values of capacitance and smallish value resistor so long as the load isn't huge (like with a preamp) and get very good filtration without spending money on chokes.

 

SS diodes also have a very small forward voltage drop no mattter the load, usually .6v. A tube recitifier can have a large value internal impedance, this comes into play with amps that has a varying load like with Class AB amps, it adds compression. One way around this is to use a L input filter instead of a C input filter. I will save that rant for another time.

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