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?

Ag insider logo xs@2xbruce19

I don’t think there is anything close to a perfect correlation between electrical performance and preferred sound.  That is why tube gear is preferred by many, myself included, even if measured performance is not better.  The same probably applies to rectifiers vs. diode bridge.  A local dealer who also makes tube gear uses both.  He recently found an electrical engineer who designs, builds, and repairs gear as a sideline.  Although he is new to the shop, he makes bold decisions.  He took home to repair one of the shop’s custom build.  After fixing it, he said he was thrilled with the sound but thought that an amp this good deserves a tube rectifier and converted it without bothering to get permission.

I use tube rectifiers in my builds, partly to conform with the vintage circuits I’m trying to replicate, and partly because I prefer the sound. Even with ultra-fast diodes I can still hear a slight coarseness and reduction of fluidity and "air." OTOH there tends to be an improvement in the bass response, so it’s a bit of a trade-off. Another advantage of, say, a 5AR4, is the slow warm-up. With solid-state diodes you can, of course, add a delay circuit, but this adds more complications to the build.

That said, a lot of very nice vintage tube amps used diode rectification--the HK Citation II, the Eico HF-87, the Fisher 500C, among others--and very few tube-lovers will take issue with the sound of those pieces. And for anything above 30-40 watts per channel, solid-state rectification is probably a better way to go. And like any other audio design, you can voice the amp in many different ways to compliment the power supply design you choose.

For my purposes I stick with tube rectifiers because to my ears, and within the limits of the amplifiers I build, it’s just a nicer sound.

I would just add that, in the case of well-designed tube equipment that enjoys a reputation for excellent sound, trust the designer. ;-)  Someone like Steve Deckert certainly makes a choice that works best for him and his customers.

I'll be the devil's advocate here. I just bought an all-tube higher end preamp that uses all tube except for the rectification. It even has a tube voltage regulator. My concern about tube rectification was the heat generated and the high failure rates of these tubes. It seems like every time I read a post about some tube equipment's failure it's the rectifier tube. This is just my personal opinion and I'm sure the tube makes a difference in the sound but by how much. I chose lower heat and reliability over the small amount of possible sound improvement for my purchasing decision. Just my .02.