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Why tube rectification?

This question is directed at the distinguished members of the forum who design and build tube amps or those who have knowledge of tube amp design. All the tube amps I own/have built us two diodes for rectification. Diodes are cheap, compact and last the life of the amplifier in most cases. Examples include the Dynaco ST-35, the Decware Zenkit1 (which is basically a Decware SE84) and the Elekit TU-8900. All reasonably well respected amps. Yet many of the more expensive amps go with tube rectification, which obviously involves the downside of another tube, more power, more space.

These two competing solutions both supply the basic power to the audio tubes and output transformers, so only indirectly interact with the sound signal. I have not read anything that explains what tube rectification brings to the party. But it must have some upside to offset it's obvious downsides. If I changed over one of the above amps to tube from diode rectification what would I be likely to  hear?

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atmasphere's avatar
atmasphere
11,793 posts
 

there is no reason to have voltage sag at higher power with tube rectified equipment if the proper rectifier tubes are chosen.

@invalid Yes- I like the plural of the word as you chose, as that is what is needed. For example the Dyanco ST70 was designed with one rectifier tube when they really needed dual rectifiers. Because they cheaped out on this issue, the 5AR4 is more likely to fail than any other tube in the amp. You would need a number of tube rectifiers to really prevent sag. It is the Voltage sag which is why blues players in particular really like tube rectifiers in guitar amps.

IOW there really isn't a good reason to use them in a tube amp meant for home hifi use other than the nice glow. But the designer might not have figured out how to keep solid state rectifiers quiet so resorted to a tube rectifier instead. Tip: HEXFRED rectifiers are nice and quiet; so much so they often need no snubbing at all. They can handle high Voltage and currents that no tube rectifier used in the home can hope to match. So in a tube amp they can work quite well.

 

sounds_real_audio
1,012 posts
 

Because it sounds better.

toddalin's avatar
toddalin
238 posts
 

My Melton MKT-88 uses dual rectifier tubes and no feedback.  I actually prefer the sound of my solid state Yamaha RX-Z9 in "Pure Direct" mode.  The Melton rolls off the highs a bit more than my liking.  But I only have about 60 hours on it.

invalid
1,186 posts
 

I like unconventional rectifier tubes, such as the 3b22, 866a, 3b28, also TV damper diodes work very well. The mainstream rectifier tubes don't even come close to the tubes I've mentioned, also these tubes can be used for a full bridge rectifier, and the mainstream rectifier tubes can't be because they all have a shared cathode.

larryi
3,981 posts
 

Well, I wonder if you would like the "unconventional rectifier" in the power supply of my phono stage.  It runs twin 300B tubes as rectifiers.

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