My Melton, with a rating of 80WPC from the four KT-88s, uses two 5Z4Ps.
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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@invalid This is an interesting assertion. If you were building a 60 Watt PP amp based on KT88s what rectifier would you use? |
@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. |
If the equipment is already designed with solid state rectifiers then yes, there are HEXFREDs rated at 1200V with plenty of Amperage.
@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). |
@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! |
@larryi the 300b can work for lower power equipment like a phono stage. Power tubes can be used as rectifiers, I wouldn't use them for high powered tube amps, but they can make lower power equipment sound really good. |
I like unconventional rectifier tubes, such as the 3b22, 866a, 3b28, also TV damper diodes work very well. The mainstream rectifier tubes don't even come close to the tubes I've mentioned, also these tubes can be used for a full bridge rectifier, and the mainstream rectifier tubes can't be because they all have a shared cathode. |
@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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@atmasphere there is no reason to have voltage sag at higher power with tube rectified equipment if the proper rectifier tubes are chosen. |
Hey Booerbillone @onhwy61 You make the excellent point that tubes are sometimes beloved precisely because of the distortion they are capable of. Great example! |
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. |
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. |
Voltage drop across the rectifier, especially when the amp is making power, is one very large reason rectifiers can affect the sound. The other reason is noise. Solid state rectifiers are often blamed for making noise but its really how the power transformer interacts with the rectifiers. Between the two an electrical resonance can occur which is set into oscillation by the rectifiers turning on and off. The resonance might be at 2MHz but can cause the rectifiers and transformer to make noises much lower in frequency, which can leak into the signal chain and cause IMD. This is known as a 'swept resonance'. Its not something you often run into with a tube rectifier. But it can be solved with proper application of snubber networks. The best approach is a small capacitance in series with a resistor across the input to the rectifier(s), directly across the output of the transformer. Once the swept resonance is shut down there's no going back to tube rectifiers as the power supply sags less at higher power levels- which makes for less distortion at those power levels. An obvious advantage of a solid state rectifier is the capacitances in the power supply can be quite a lot higher. There is often a fairly low limit to capacitor values when tubes are used. There are timing constants involved with these values. What you want is that none of the timing constants in the amplifier circuit be lower than those in the power supply- else the amp can much more easily modulate the power supply, resulting in higher distortion. |
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. |
I will add something that has not yet been mentioned explicitly. What you are listening to from an amp/pre-amp is the power supply - not the signal being sent to it.
It is a bit of a misnomer that we call these things amplifiers. It implies that the signal itself is being amplified, and the other stuff is just there to help. What is in fact happening is that the voltage from the power supply is being modulated by the input signal, and the input signal itself is swallowed by the tube/transistor. So what happens is the voltage from the power supply is either directed to ground or to the speaker, and the input signal simply regulates how much of that goes where.
This is why power supplies, especially in preamps and DACs, are so critical. You are literally listening to the sound of the rectifier after is has been smoothed out by some capacitors.
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if you end up taking tube rectification, you may find that rolling tubes offers a very clearly different character and weight of presentation. The manufacturer installed NOS AZ4 tube in my 4w +4w SET from Japan sounds fine, yet a contemporary production AZ4 mesh plate from EML gives much greater scale and dynamics, totally transforming performance of the amplifier, and EML seem to last notably longer than expected. Others have reported on this. YMMV. |
In our opinion, done correctly, tube rectification sounds better in our designs to our ears. In repairing components, we find that not using tubes was a short cut and cost savings. Once done right, it can be glorious. All designers who use tube rectification in our opinion, again, does not make the sound that we achieve in our designs, Lamm included. Not to say they sound not as good, but you have to hear the differences when compared to each other. @whart - agree with your findings, but those units can be upgraded to achieve the sound you prefer. Happy Listening. |
I used a Lamm L2 line stage for a number of years--solid state audio path, separate tube rectified power supply. Gorgeous mids, a bit rolled off at the frequency extremes, but you could not say it sounded euphonic or analytical-- it sounded very much like music. That model has since been updated. I'm currently using the Veloce Lithio 2.0 with the updated batteries and some other changes. I do roll the rectifier in my Allnic H3000- have quite a few grails. My preference, which is based in part on how the overall system is voiced, is a GEC u-52 cup base. I have a Mullard metal base (really a Philips-Miniwatt). Bass is phenomenal, far better than the bakelite version that followed, but lacks the finesse and airiness of the GEC in my system. Some of this may be system dependent. |
@willywonka I don't know why tube equipment manufacturers don't use rectifier tubes such as the 3b22 or 3b28, I have had no problems with these rectifier tubes even if I leave them on 24/7 for months at a time, plus they can be used for high wattage power amps. These types of tubes also have very good regulation as they drop a constant 15 volts up to there operating limits, which are very high. I think the reason they are not used more often is the cost of the filament current that the transformer has to have. |
Nothing wrong with that choice, IMO. Generally tube rectifier failures occur in power amplifiers with high current draws. The Dynaco ST70 is notorious for eating Chinese 5AR4s. In a preamp there usually isn't enough current being drawn to worry about a tube rectifier failing. But there are exceptions. The 6X5, used in a number of tube preamps, is not very robust and I've had at least one fail. |
I'll be the devil's advocate here. I just bought an all-tube higher end preamp that uses all tube except for the rectification. It even has a tube voltage regulator. My concern about tube rectification was the heat generated and the high failure rates of these tubes. It seems like every time I read a post about some tube equipment's failure it's the rectifier tube. This is just my personal opinion and I'm sure the tube makes a difference in the sound but by how much. I chose lower heat and reliability over the small amount of possible sound improvement for my purchasing decision. Just my .02. |
I use tube rectifiers in my builds, partly to conform with the vintage circuits I’m trying to replicate, and partly because I prefer the sound. Even with ultra-fast diodes I can still hear a slight coarseness and reduction of fluidity and "air." OTOH there tends to be an improvement in the bass response, so it’s a bit of a trade-off. Another advantage of, say, a 5AR4, is the slow warm-up. With solid-state diodes you can, of course, add a delay circuit, but this adds more complications to the build. That said, a lot of very nice vintage tube amps used diode rectification--the HK Citation II, the Eico HF-87, the Fisher 500C, among others--and very few tube-lovers will take issue with the sound of those pieces. And for anything above 30-40 watts per channel, solid-state rectification is probably a better way to go. And like any other audio design, you can voice the amp in many different ways to compliment the power supply design you choose. For my purposes I stick with tube rectifiers because to my ears, and within the limits of the amplifiers I build, it’s just a nicer sound. |
I don’t think there is anything close to a perfect correlation between electrical performance and preferred sound. That is why tube gear is preferred by many, myself included, even if measured performance is not better. The same probably applies to rectifiers vs. diode bridge. A local dealer who also makes tube gear uses both. He recently found an electrical engineer who designs, builds, and repairs gear as a sideline. Although he is new to the shop, he makes bold decisions. He took home to repair one of the shop’s custom build. After fixing it, he said he was thrilled with the sound but thought that an amp this good deserves a tube rectifier and converted it without bothering to get permission. |
I don't do the EE' thing. I leave that to the EE's who do design and build my Tube Equipment. I own Tube Pre Amp - Phonostage - DAC - Power Amp, of which all are Bespoke Design Commission Builds from a selection of EE's who have Valves as their Electronics of Interest. For the record, I also know a selection of EE's that live and breathe SS Circuitry and who would not express and interest in a Valve Design. In relations to Phon's the Best Phon's heard is from my Assessment is designs produced by the Tube EE's I know. In the same area, the best SS Phon' from my assessment that has been heard, is produced by a known EE who does not get stimulation from Valves. I choose Phon's as a description as I have heard over the Years, phon's at Bake Off's that can have a collective value to well over £100K, with £10K commercial phon's being present for comparisons. In relation to Tube Rectification on a Power Supply, the design does have the capability to influence the end sound. Again on the Phon' I own, O have heard it used with a few different Power Supply Designs and each did effect the end sound. The other 'Valvuable' This type of interaction with a Circuit where EE skill levels can be low in relation to typical EE concerns, is where Tubes and Tube Rolling is a winner. If an inexperienced with EE requirements Individual is OK with the cost to be incurred as a result of choosing to Tube Roll, that individual can make discoveries about end sound that is available with ease. Such an experience is not as easy to reproduce with SS Circuits. In relation to tweaking with SS Circuits, I have the Option on the Tube DAC to exchange a Filter CHIP, which has a multi pin connection to the Circuits soldered base for the CHIP to plug in to. The EE Designer has supplied a selection of CHIP's that have obvious evidence of having been modified, I suppose to meet the end sound that the EE is wanting, their own Signature in the CHIP to produce sound and not that of the Manufacturer. Exchanges of these CHIP's for somebody with my experience is precarious and much much more difficult than swapping out a Tube. Concern for damaging very fragile pins where having a visual observation is very limited, does justify the concerns, Hence, CHIP Filter changes that are readily at hand are not a common experience. |
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. |
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?
thing about a Tube used for the Rectification, is that the Tube can be Tube Rolled. A very good end sound / options for an end sound, can be discovered as a result of experiencing a range of tubes as part of the process for making a tube selection.