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.
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
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. |
@invalid Yes- I like the plural of the word as you chose, as that is what is needed. For example the Dyanco ST70 was designed with one rectifier tube when they really needed dual rectifiers. Because they cheaped out on this issue, the 5AR4 is more likely to fail than any other tube in the amp. You would need a number of tube rectifiers to really prevent sag. It is the Voltage sag which is why blues players in particular really like tube rectifiers in guitar amps. IOW there really isn't a good reason to use them in a tube amp meant for home hifi use other than the nice glow. But the designer might not have figured out how to keep solid state rectifiers quiet so resorted to a tube rectifier instead. Tip: HEXFRED rectifiers are nice and quiet; so much so they often need no snubbing at all. They can handle high Voltage and currents that no tube rectifier used in the home can hope to match. So in a tube amp they can work quite well.
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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