Tube if pared with a choke everyday. SS if no choke.
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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- 35 posts total
Hello Bruce 19. The reason to use tube rectifiers is that the high votage builds up slowly (versus instantly) and that avoids the schock of WHAM! all the capacitors in the unit are suddenly awakened from their fully discharged condition by the appliction of full power. This is particularly tough on the filter capacitors in the power supply. I once bought a used Adcom reciever at a very good price. I took it home and plugged it in and hit the power switch. A FLASH, a POW! and the room was FILLED WITH SMOKE. The unit had not been used in a looooong time. The electrolytic capacitors commonly used i power supplies are essentially a dead short when power is applied. The voltage causes a layer of bubbles to form inside the capacitor and that is the insulation between the "plates" of the capacitor. An old, perhaps physically dried out capacitor doesn't form the layer of bubbles quickly enough (if at all) to stop the flow of current through the capacitor. The bridge rectifier dumped all the current that could make it from the AC line, thru the fuse and into the essentially dead shorted capacitors. It takes time for a fuse to blow. Just enough time for the capacitors to explode, the solid state rectifier (diodes) to become cinders and the smoke to fill the room. Interestingly, the circuitry in the receiver never felt the operating voltage and was undamaged. I've got the power amp section running and the tuner section, but the line amp section is not working yet. It will, just as soon as I can find the time to fix it. Happy Listening. |
In guitar amplifiers tube rectification is revered. The class Fender and later Marshall amps all had tube rectifiers and the sound they produced is a touchstone for virtually every guitar amplifier since. If you turn up the volume and strike hard on the strings the tube rectifier's relative slowness or sag acts as a compressor and gives a sound that's described as a cream like texture. Mesa Boogie has offered a Dual Rectifier tube or silicon selectable line of amps for decades. |
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 there is no reason to have voltage sag at higher power with tube rectified equipment if the proper rectifier tubes are chosen. |
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?- 35 posts total