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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?

Ag insider logo xs@2xbruce19
jond's avatar
jond
5,849 posts
 

I will say this in my amps that have tube rectification the rectifier tube has a definite effect on the sound. That said I've also listened to very good amps that are SS rectified so there's more than one way to skin the cat.

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bruce19 OP
249 posts
 

Thanks @jond. One additional benefit of tube rectification might be for some that it adds to the cool look. They are usually pretty big tubes and so add visual impact. I am learning not to discount visual impact as quite important in our sound based hobby :-)  I hope we get some more input on this.

gs5556
1,235 posts
 

Tube rectifiers develop a larger forward voltage drop than silicon rectifiers (up to 50 volts for the tube vs about 2 to 3 volts for the diodes) so that may have quite an effect on the amp as it will change the operating parameters. I would vote No on that one.

I have used both tubes and diodes. Nowadays there really is no reason to go with tube rectification because it’s biggest advantage of being quiet can be rivaled with the Ultra Fast Reverse Recovery diodes (ie UF4007). I can buy a thousand of them for the cost of one NOS rectifier.

How I chose a rectifier is dependent on the amp. When I built my single ended 2A3 mono’s I was looking for the Old School look and sound. I find the 5Y3GT rectifier has a certain synergy with the 2A3 tube, bringing out its character better than others I’ve tried. And the extra glowing orange light just adds to the feel. However, when I built a pair of KT150 60-Watt A/B push-pull triode/Ultralinear, I opted for the UF4007. First reason was I needed 430 volts, and with tube rectifiers I would have to go with a higher voltage transformer and then use 600V capacitors. Those are harder to source, are much bigger and more expensive. Second, the amplifier was fitted with delay start, fixed bias voltage, LED indicator lights, fault protection circuits and circuit breaker trip switch. All that required a printed circuit board, making it much easier to populate the overkill power supply on the board than screwing tag boards and parts all over the chassis. In this case, solid state met the performance objectives.

That’s basically it. No advantage of one or the other just on their own standing, at least in my opinion.

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