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.
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?
Showing 5 responses by bruce19
That is a good observation @joshua43214, yet, while I don’t doubt those who have said that changing rectifier tubes changes the sound, I do struggle a bit to understand why. After all if they are doing their job they should just be truning AC into inperfect DC, then the following caps, resistors and maybe inductors all smooth the DC. The real important thing about a power supply as I understand it is that it supplies clean and plentiful power. The audio signal doesn’t interact at all until the gainstage or preamp tubes and then again in the power tubes. So that is where desireable tube distortion or "tubiness" enters the picture. Now it is plausible that Rectifier tubes may introduce their own flavor of distortion into the power flow and that carries though to the final output. I can buy that and also accept that it might be desireable. My own thinking on hifi these days is that music performance is to music reproduction as live viewing of a landscape is to an image of the landscape. Different expectations apply in each case and in the latter two intentional modification for effect is entirely permissible. That is, tone controls on an amp are just as permissible as impressionistic painting or jiggering the exposure of photos. |
Hey Booerbillone @onhwy61 You make the excellent point that tubes are sometimes beloved precisely because of the distortion they are capable of. Great example! |
@atmasphere , your mention of a better diode brought me to attention like a retriever near a duck pond. I went right to Mouser to learn a bit more and I would like to try subbing them into my Decware Zenkit1 and possibly my Dynakit ST-35. The Zenkit uses a pair of Vishay RGP10M-E3/54 diodes and the Dynakit uses a pair of IN4007 diodes. Could appropriate HEXFRED diodes be used to replace the existing diodes in each amp without other modifications? The Zenkit is more of interest because that power supply has been troublesome from the start. Initially it had ~60-120 hz hum problems that I reduced by adding more capacitance to the power supply. But lately there has been an intermittent sound while playing that is more in the 1000-2000 hz range. Your mention of oscillation caused by the solid state diodes around 2 khz earlier in this thread make me think this could be diode related. The St-35 has been nice and quiet right from the start so I may not mess with that unless it seems there is something to be gained. Tell me more and thanks for being generous with your experiance as in the past! |
Can't that problem be solved with a thermister in the path of the incoming AC mains line? I have only added them when called for by the designer but I don't think they would do any harm. Just slow the flow of AC while the thermistor gets up to temperature. No?