• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Correct Path: Diodes Or Rectifier Tube?

Both paths are correct.
Build a SET with both properly designed recitification methods and switch between them. The end is decided by your ear.

The other question is are you a purist? In that case stay with tube. Personally, my own journey has led me to build with SS rectification on full range power amps and Vacuum rectifiers in my line stages.
 
Am I on the right path? Does tube rectification sound "better"?

Not necessarily. For quite some time, SS rectification has lead to better bass. Unfortunately, all PN junction diodes generate switching noise. That noise is objectionable. Vacuum rectifiers don't produce that noise. Fairly recently, high PIV Silicon carbide (SiC) Schottky diodes were introduced. Schottky diodes are "noiseless", while retaining the other virtues of SS rectification.

My advice is that you rectify the B+ with high PIV Schottky diodes.
 
Yeesh, build an amp correctly, it's not hard to neutralize switching noise.

BTW, schottky diodes are equally capable of producing noise in switching circuits. They may not have charge storage, but the dramatically higher junction capacitance near forward bias looks the same. I once made a pulse generator with a schottky:

[IMGDEAD]http://myweb.msoe.edu/williamstm/Images/DSRPG3_4.jpg[/IMGDEAD]

Unfortunately, the contrast on my scope at the time was poor, but you can just barely see a very narrow downward blip at 6.8 div from the left. This occured when the junction capacitance of this particular diode went from about 3nF near forward bias to about 100pF in reverse bias. You get the same charge delivery effect which makes inductors go "splat", which includes stray wiring inductance.

The solution is simple, add an R+C damper, typically 0.01uF + 100 ohms, right across the diode, and keep your rectifier wiring away from signal current paths.

Tim
 
Hi!

So what is the down side with simply using a tube foe rectification? Is it softer bass? Higher distortion? Inquiring minds want to know.

There is no simple answer to this. It totally depends on the curcuit which is supplied. A SE amp will react differently than a PP. Class A different than Class AB. Even within the same class of amp not each circuit will react the same. Try it and listen for yourself!

Thomas
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
So what is the down side with simply using a tube foe rectification? Is it softer bass? Higher distortion? Inquiring minds want to know.



Just for interest,

Tube rectification.

Volt drop across the tube is higher than with diodes.
However different diodes "sound different".
It all comes down to personal taste!

You can snub diodes again this alters the perceived sound.
The type of music you listen to and the expectation of what you think "Tube sound" sounds like!

The harmonic content of the amplifier will also make a difference!

I know this is going to create more questions than answers, however there is no direct answer to what you would like / dislike.

Some people don't think that HIFI sounds like a tube amp should sound!
(Old valve radios sound is nice, However it is not HIFI!):)


Regards
M. Gregg
 

Structo

Member
2010-12-16 12:45 am
Oregon
On my guitar amps I routinely bypass the diodes with .01uF ceramic caps.
I use the Ultra Fast UF5408 diodes.

This is to snub the transient noise.

I haven't looked on a scope to see this or if it actually works.
It's just something I have always done.

But I was reading a book last night that talked about diode ringing and that the caps help prevent that resonant from forming as well.


As was mentioned, tube purists can't even stand the mere suggestion of using any Silicon based products in their amps while many others tolerate that bit of modernization in the power supply.
Trade off can be a better regulated power supply and tighter bass due to increased filtering.
I have also heard that you can hurt the tone with too much filtering so there is probably an equation somewhere that addresses that.
 
So what is the down side with simply using a tube foe rectification? Is it softer bass? Higher distortion? Inquiring minds want to know.


Are inquiring minds also lazy bums? Nothing comes close to first hand experience.

My subjective impressions are indeed softer bass and less distortion/more resolution elsewhere. I always use high performance regulators, at least to power the small signal stages, but the bass remains softer than SS rectifires. SIC Schottkys didn't work for me. A sonically acceptable compromise are mercury rectifiers (great bass) if you can live with all their idiosyncrasies. Turns out i can't.
 
Tube rectification is much softer than SS.

I have had problems switching high voltages with diodes with switching spikes.
Had to add capacitors across the diodes to stop the glitches getting on the audio.


That's the Physics of PN junction diodes at work. The same phenomenon of minority carrier injection BJTs depend on for their operation causes the troublesome reverse recovery spike. Being majority carrier only, Schottky diodes don't exhibit the spike.
 
That's the Physics of PN junction diodes at work. The same phenomenon of minority carrier injection BJTs depend on for their operation causes the troublesome reverse recovery spike. Being majority carrier only, Schottky diodes don't exhibit the spike.

I use a couple of schottky diodes in my class D amplifier.
 

kevinh

Member
2007-05-08 4:19 am
Lynn Olsen has some interesting comments on recitifcation and it's effect on sound.

From his nutshellhifi website:

Moving on to the main B+ supply, I first tried a 5R4-GY rectifier (a traditional choice for 300B circuits), but was dismayed with the arc-overs and poor reliability in several examples. Maybe they were old and weak, but this sort of failure should never happen in the first place. By contrast, TV damper diodes, including the New-Old-Stock 6C*3 family and the new Svetlana 6D22S, have more-than-ample peak curves, and derating for continuous use gives more headroom in current and voltage than the traditional tube rectifiers seen in 2A3 or 300B amps. The low voltage drop (15V), huge peak currents (2A), and slow warm-ups (30 seconds) are just additional bonuses.

Matt Kamna also demonstrated a technique for zooming in on the waveform on the power-transformer secondary (about 10V/div on the scope screen). The rough appearance around the zero-crossing was very obvious with solid-state diodes. HEXFRED's gave a small improvement, but conventional tube rectifiers looked much smoother, and the TV damper diodes were by far the smoothest of all. So even in low-current preamp applications, TV damper diodes give the least noise. I know from experience in the Tektronix Spectrum Analyzer division that it's much easier to eliminate noise at the source than filter it afterward. If there was an even quieter device, I'd use that, but as far as I know, TV damper diodes are the quietest from the viewpoint of switching noise. Considering that the main B+ supply is switching five hundred volts, this is not a small consideration, since switch-noise is radiated in all directions, into the B+ supply, the interior of the chassis, and back into the power cord.



The Amity, Raven, and Aurora


The page is terrific reading very informative. :cool:
 

Jen-B

Member
2010-01-17 5:03 pm
UK
My take on things...

If you can hear the rectifier (i.e. if it has an effect on the sound) then the amp is badly designed!

In guitar amps people want rectifier sound effects, which is fine, but that has no place in hi-fi reproduction. Folks who harp on about the sound of different VT rectifiers in their hi-fi amps surely want a sentimental involvement with the equipment and are not necessarily focussed on reproducing the music track accurately. All they are saying is "my amp is so badly designed that I can hear the rectifier" !

So, in my fairly inexperienced opinion, the reasons for using a VT rectifier are as follows:
1) Slow warm up of some types (GZ34?), allows the main tube to heat up before high voltgage is applied.
2) If placed on the outside of the chassis they can have a pleasant visual appeal (and there is nothing wrong with that - just admit it to yourself that sometimes you choose something because it is visually appealing - see; it's not always about performance!).
3) If it goes 'phuuut' then it is easy to change.

If you do go solid state then I guess silicon carbide Schottky are the best types. However you may want to install a timer so that your high tension is delayed until your tubes have warmed up a touch.

Bye,
J.
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Jen-B,

Quote: If you can hear the rectifier (i.e. if it has an effect on the sound) then the amp is badly designed!

I'm sorry I have to disagree.
All components have a sonic signature any component will add its own "addition or distortion to the sound". The more "open" an amp is, the more lightly you are to hear the difference! Ongaku is an example of tweaking to the extreme with components.
If what you say is true if you build Ongaku with standard components it will be as good or better. (Sound the same!)

Yes I agree that some things look better than others and yes some people prefer SS to tube. The same as some people like PP in preference to SE. We try to balance the sonic signatures to try to get a neutral sound. Please note the word try! The preference to one amp or another is the sonic signature of the circuits and components used!

If we follow your thoughts tubes do not sound different. Caps do not sound different and Diodes do not sound different. Cables do not sound different. Etc. (Its just bad circuit design)

Regards
M. Gregg
 
Last edited:
I've built a pair of highly efficient FR speakers. My next goal is to build or purchase an SET 300B Tube Amp.

I am determined to choose an amp that uses tube rectification. I believe this is the correct path to that classic tube sound.

Am I on the right path? Does tube rectification sound "better"?

Not that I've been able to tell, but so far all my projects have been PP designs. It doesn't make so much of a difference, since with PP, the OPT primary center tap is at AC ground (or at least very close to it).

So, for one project, I went with SS power diodes. It worked just great. For another project, I went with 5U4GB power diodes for the positive DC rail, since I had a NIB junk box power xfmr with a 650Vct @ 150mA secondary. The current rating was right for this project, but with SS diodes, it overvolted badly (458Vdc unloaded) and the design nominal DC was 350Vdc. The power xfmr was obviously designed to provide 350Vdc with the 5U4GB, since that's what I got with the 5U4GB and a 34uF (two 68uF/300V units in series with voltage equalization resistors).

The A Number One problem with a SS power supply is that it hits full voltage within a couple of seconds, and it takes way longer for cathodes to warm up. If you go the SS route, it's best to split the DC and heater supplies, so that you can either add an automatic delay to the HV, or manually power up the heaters, let 'em get good and hot, before switching on the HV. It's especially important if you're using DC coupling in the circuit to avoid overvolting something before the cathodes are hot enough to draw current.
 

Structo

Member
2010-12-16 12:45 am
Oregon
Isn't that what a standby switch can do for you?

Of course you want to place it in the correct spot.

If you are worried about flyback from a choke, you can put a 100K resistor across the standby switch to bleed voltage to the filters so it isn't a big shock when you apply the high voltage.
Or use a thermistor on one or both HT lines to the filters after the diodes.
If you choose the right one you can get some time for the heaters to heat up before the high voltage creeps in.

Or just use an indirectly heated rectifier like a 5AR4 and you will be good to go.

I am among the group that thinks an amp is a sum of it's parts and that most everything does and will influence the tone.
Some more subtlety than others.

Myself, even though I think I have a pretty discerning ear, years of abuse and age have damaged some aspects of it, especially the high frequencies.
But I can still hear quality when I am faced with it.
 

Jen-B

Member
2010-01-17 5:03 pm
UK
All components have a sonic signature

So, let me try and understand you… you think that if a resistor sounds ‘lush’ then playing Motorhead through that resistor will make Motorhead sound lush????

Components do not have a ‘sonic signature’; they have electrical characteristics which must be understood, selected and blended to produce the desired circuit and system response.


The more "open" an amp is, the more lightly you are to hear the difference!

Not at all, it’s just a poorly designed amp. Lots of valve amps seem to be like that. That’s OK, because it satisfies the owners who have a priority of sentimental involvement with their amps rather than accurately reproducing what is on the record / CD / etc..


Ongaku is an example of tweaking to the extreme with components.

More like an example of marketing to fools with money!



If we follow your thoughts tubes do not sound different. Caps do not sound different and Diodes do not sound different. Cables do not sound different. Etc.

Tubes seem to have tolerances of some 10 – 20% so they should perform differently.

Replacing one competent cable with another equally competent cable will not change a thing. If you do think that you hear a difference then you should investigate further, and I’ll give you a hint: it’s not the cable that has changed what you think you hear.


I stand by my original comment: If you can hear the rectifier (i.e. if it has an effect on the sound) then the amp is badly designed!

Bye,
J.
 
The solution is simple, add an R+C damper, typically 0.01uF + 100 ohms, right across the diode, and keep your rectifier wiring away from signal current paths.

Tim, could you put a single RC snubber across the secondary and get effective damping? I guess I am just having trouble seeing exactly what the parasitic elements are that we are trying to damp.