2. amps-preamps
  3. 191788-134895

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
11,922 posts
 

Could appropriate HEXFRED diodes be used to replace the existing diodes in each amp without other modifications?

If the equipment is already designed with solid state rectifiers then yes, there are HEXFREDs rated at 1200V with plenty of Amperage.

Because it sounds better.

@sounds_real_audio This is really debatable (I’m doing it right now...).

I’ve found that using properly snubbed semiconductors in the power supply sounds better and measures better than a tube rectifier. They have different design requirements of course (apparently not everyone understands how to snub them for example). If used correctly I find no tradeoffs.

FWIW, one of the best tube amps from the vintage era was the HK Citation 2, which employed a solid state supply. It was a Voltage doubler style which was common with many American tube amps (ex.: Fisher).

invalid
1,228 posts
 

@atmasphere  most tube equipment manufacturers don't use the correct tube rectifiers for higher power amplifier, most of the mainstream full wave tube rectifiers drop too much voltage at higher power.

atmasphere's avatar
atmasphere
11,922 posts
 

@invalid This is an interesting assertion. If you were building a 60 Watt PP amp based on KT88s what rectifier would you use?

toddalin's avatar
toddalin
296 posts
 

My Melton, with a rating of 80WPC from the four KT-88s, uses two 5Z4Ps.

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