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Old 25th December 2010, 11:30 PM   #11
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Quote:
Originally Posted by nigelwright7557 View Post
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.
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Old 25th December 2010, 11:34 PM   #12
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Originally Posted by Eli Duttman View Post
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.
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Old 26th December 2010, 12:51 AM   #13
kevinh is offline kevinh  United States
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Lynn Olsen has some interesting comments on recitifcation and it's effect on sound.

From his nutshellhifi website:

Quote:
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.


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The page is terrific reading very informative.
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Old 26th December 2010, 04:22 PM   #14
Jen-B is offline Jen-B  United Kingdom
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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.

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Old 27th December 2010, 10:06 AM   #15
M Gregg is offline M Gregg  United Kingdom
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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
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Last edited by M Gregg; 27th December 2010 at 10:13 AM.
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Old 27th December 2010, 04:23 PM   #16
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Tube rectifiers have a larger internal resistance than ss diodes. When more current is needed the voltage drop across it will be bigger -> lower B+

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Old 27th December 2010, 07:07 PM   #17
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Quote:
Originally Posted by JimOfOakCreek View Post
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.
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Old 27th December 2010, 07:18 PM   #18
Structo is offline Structo  United States
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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.
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Old 28th December 2010, 12:31 AM   #19
Jen-B is offline Jen-B  United Kingdom
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Quote:
Originally Posted by M Gregg View Post

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.


Quote:
Originally Posted by M Gregg View Post

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..


Quote:
Originally Posted by M Gregg View Post

Ongaku is an example of tweaking to the extreme with components.
More like an example of marketing to fools with money!



Quote:
Originally Posted by M Gregg View Post

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.
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Old 28th December 2010, 04:01 AM   #20
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Quote:
Originally Posted by Sch3mat1c View Post
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.
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