Rectifier Tube Concerns

[SwedishChef]

I'm a tube noob, please go easy on me for my ignorance.

Rather than take my Blue Velvet preamp post way off track, I decided to start a new thread that just pertains to rectifier tubes.

Here is my main question and concern at the moment, why is the 5U4G the choice of so many audio enthusiast when this tube is not a slow warm? Further, I am also hearing the 5U4G draws 3A versus the other rectifiers drawing 2A so if your transformer is not wound for 3A you can actually burn up your transformer. Is the 5U4G so great and magical that people risk the surge, and they also beef up all the components to run this rectifier tube? What am I missing here?

The seller that I purchased my first Sylvania 6SN7 pair from on eBay is sending me a 5V4 rectifier to replace my Chickidy China 5Z4p and he suggested that I only use a 5V4 or 5AR4 rectifier tube in my Blue Velvet Pre, mainly because the current draw of the 5U4G and the surge could cause me some problems. These seem to be valid concerns, even from a tube noobs perspective. He went on to say that a quality NOS 5AR4 rectifier would likely last me forever in that circuit. As lazy as I am, the forever replacement is actually very appealing to me.

I'd also like to know why the hell are WE274 rectifiers so damn expensive? I just wanted to replace the 5Z4p China junk that my preamp comes with, I understand that certain tubes may be rare or way more valuable than others. But why is a Westinghouse WE274 worth more than it's weight in gold? It's not rare. People have NOS laying around, is demand actually that high for this rectifier tube? Is this the Holy Grail rectifier tube? Is there some kind of bass punch and crazy wow factor the WE274 provides? Some don't hear any difference in rectifier upgrades.

When you watch those stupid rectifier shootout videos on YouTube, they don't give you all this other pertinent information about the tube they like.

 

[cademan]

You should read up on rectifier tubes and how they work. The 5U4 has a directly heated filament and by design, draws 3 amps. The directly heated rectifier has a faster warm up time due to when the filament starts to glow.

I won't go into it because there is too much to learn and know but the 5Y3 is a smaller version of the 5U4 and by design, only uses 2 amp filament draw. These rectifier tubes take their high voltage taps straight off of one side of the filament. You will also have to read up on how that works.

The 5AR4, 6X4, 6CA4 types of rectifier tubes are known as indirectly heated rectifier tubes as they take their high voltage right off of the cathode and not the heater. These ones take a little more time to warm up.

Depending on the high voltage needs and current demands and transformer winding configurations, any one of these tubes can be used in an amp depending on its factory or DIY design.

Tube data sheets will reveal why a 5U4 would be better than a 5V4 and vice versa. The 5V4 actually drops more voltage than a 5U4 so unless you want 20 volts or less in your amplifier, don't use the 5V4 in place of the 5U4.

And stop watching those youtube videos where the person doesn't know what they are talking about.

Watch videos by Uncle Doug, Mr. Carlson's lab, D-labs, and BlueGlow electronics videos.

 

[peterh]

A pair of un4007 will replace any of the above.

 

[gadget73]

If the power transformer can handle it, the 5U4 is a good option because its both robust and cheap. The whole fast startup thing is an over-hyped concern IMO. Rate the caps appropriately for the voltage spike and its not a problem.

obviously if the transformer can't run a 3 amp filament, its a bad choice. There are plenty of 2 amp rectifiers out there, but other than the 5AR4, none of them will handle the current that a 5U4 will. In a preamp its pretty hard to imagine needing any significant current capacity though so you have a choice of basically anything.

Western Electric tubes cost a fortune because they are Western Electric tubes.

the other trick with switching rectifiers, they have different voltage drops so the thing ends up running differently as a result. The various rectifiers have different requirements for transformer resistance and max first cap too, so its hard to design a power supply that can run any rectifier unless its designed around the wimpiest one around.

 

[SwedishChef]

You should read up on rectifier tubes and how they work. The 5U4 has a directly heated filament and by design, draws 3 amps. The directly heated rectifier has a faster warm up time due to when the filament starts to glow.

I won't go into it because there is too much to learn and know but the 5Y3 is a smaller version of the 5U4 and by design, only uses 2 amp filament draw. These rectifier tubes take their high voltage taps straight off of one side of the filament. You will also have to read up on how that works.

The 5AR4, 6X4, 6CA4 types of rectifier tubes are known as indirectly heated rectifier tubes as they take their high voltage right off of the cathode and not the heater. These ones take a little more time to warm up.

Depending on the high voltage needs and current demands and transformer winding configurations, any one of these tubes can be used in an amp depending on its factory or DIY design.

Tube data sheets will reveal why a 5U4 would be better than a 5V4 and vice versa. The 5V4 actually drops more voltage than a 5U4 so unless you want 20 volts or less in your amplifier, don't use the 5V4 in place of the 5U4.

And stop watching those youtube videos where the person doesn't know what they are talking about.

Watch videos by Uncle Doug, Mr. Carlson's lab, D-labs, and BlueGlow electronics videos.

I have been reading data sheets and rectifier information every chance I get. I am leaning more towards the 5AR4 now since it seems like it's also recommended often. Will check out the Uncle Doug videos tonight!

 

[Mybig8ohm]

I am pretty new to tube amplification myself but I've had a couple tube preamps based on the Chinese 5Z4P rectifier. One of the preamps was very sensitive to rectifier tubes, meaning that there was a noticeable difference in sound and bass output depending on what rectifier was used. My 2 favorites are the England/UK made Brimar 5z4g and the England/UK made Tungsram 5Z4G. I currently use the Tungsram, seems to add a bit of extra bass in my set up..I think it's an awesome tube.

The ones I've used were from the 50's and 60's, and the prices are so jacked up it's hard to find any on the cheap. I've tried 5AR4's in its place but they were newer "re-issued" tubes and I didn't like them as much. Unfortunately in my brief experience with rectifier tubes I find the NOS tubes do sound better. Although I'm open to any suggestions of good newer re-issues. I did purchase a 60's Mullard 5ar4/Gz34 which literally transformed the sound of my tube amp, I imagine it would work well in my preamp too if needed. I was told I could replace a 5z4p with a 5ar4, but not the other way around.

Since I don't know much about tube gear, (though I'm learning) I now try to stick to what the manufacturer or builder recommends. With the 5z4p tube pre I've tried the 5ar4/Gz34, 5v4g, 5y3, 5y3gt but I feel more comfortable sticking to a 5z4g.. especially the 2 I had mentioned.
Good luck, I hope you are able to find what works/sounds best in your setup. Tube "rolling" can be fun, but I also find it can be extremely expensive and a pain in the butt compared to solid state lol.

 

[Lavane]

I am pretty new to tube amplification myself but I've had a couple tube preamps based on the Chinese 5Z4P rectifier. One of the preamps was very sensitive to rectifier tubes, meaning that there was a noticeable difference in sound and bass output depending on what rectifier was used. My 2 favorites are the England/UK made Brimar 5z4g and the England/UK made Tungsram 5Z4G. I currently use the Tungsram, seems to add a bit of extra bass in my set up..I think it's an awesome tube.

The ones I've used were from the 50's and 60's, and the prices are so jacked up it's hard to find any on the cheap. I've tried 5AR4's in its place but they were newer "re-issued" tubes and I didn't like them as much. Unfortunately in my brief experience with rectifier tubes I find the NOS tubes do sound better. Although I'm open to any suggestions of good newer re-issues. I did purchase a 60's Mullard 5ar4/Gz34 which literally transformed the sound of my tube amp, I imagine it would work well in my preamp too if needed. I was told I could replace a 5z4p with a 5ar4, but not the other way around.

Since I don't know much about tube gear, (though I'm learning) I now try to stick to what the manufacturer or builder recommends. With the 5z4p tube pre I've tried the 5ar4/Gz34, 5v4g, 5y3, 5y3gt but I feel more comfortable sticking to a 5z4g.. especially the 2 I had mentioned.
Good luck, I hope you are able to find what works/sounds best in your setup. Tube "rolling" can be fun, but I also find it can be extremely expensive and a pain in the butt compared to solid state lol.

I've been happy with the TAD GZ-34's with the brown base. They had them made to there own specs. The factory thst was making them isn't in business anymore, so they're having them made elsewhere now with a red base. I don't know it they are as good though. I haven't had one fail yet.

 

[Mybig8ohm]

Thank you Lavane for your input. I had read good things about the TAD rectifier on-line, good to hear from someone with experience with it. I had also seen mention of good EL34's made by them.

 

[FlaCharlie]

why is the 5U4G the choice of so many audio enthusiast when this tube is not a slow warm? Further, I am also hearing the 5U4G draws 3A versus the other rectifiers drawing 2A so if your transformer is not wound for 3A you can actually burn up your transformer. Is the 5U4G so great and magical that people risk the surge, and they also beef up all the components to run this rectifier tube? What am I missing here?

The seller that I purchased my first Sylvania 6SN7 pair from on eBay is sending me a 5V4 rectifier to replace my Chickidy China 5Z4p and he suggested that I only use a 5V4 or 5AR4 rectifier tube in my Blue Velvet Pre, mainly because the current draw of the 5U4G and the surge could cause me some problems. These seem to be valid concerns, even from a tube noobs perspective. He went on to say that a quality NOS 5AR4 rectifier would likely last me forever in that circuit. As lazy as I am, the forever replacement is actually very appealing to me.

The requirements of an amplifier and preamp are quite different, so while a 5U4 might be a great choice for an amp, I can't imagine why anyone would use a 5U4 in a typical preamp since the current draw will be so much lower than an amplifier. And, as you point out, it also requires more heater current. It will work as long as the power transformer can supply the heater current but, as I see it, it's not the best tool for the job.

I generally use indirectly heated rectifier tubes and other slow start schemes in my DIY projects purely on the theory that slow start is less stressful. I used a 6CA4 / EZ81 in my Boogie Factor preamp, for example. But I also have lots of vintage gear that uses directly heated rectifiers, including the 5U4, and there don't seem to be any reliability issues. So I wouldn't be too concerned with the directly vs indirectly heated issue.

If you've got an octal socket and 5v heater then a common 5Y3, which uses only 2A of heater current, would be a better choice. If you want slow start, there are a couple of 5Y3 variants that are indirectly heated - the 6087 and the 6106.

Personally, I would not spring for an expensive NOS 5AR4. The advantage of NOS, or even used old stock, 5AR4s is that they are tougher than the new production versions. This makes a difference in an amp where they are under more stress. But if I was going to use a 5AR4 in a preamp I would think that a decent (meaning anything besides a JJ) new production version would work just fine and not cost nearly as much. Really, any 5AR4 is overkill for a preamp, though.

When you watch those stupid rectifier shootout videos on YouTube, they don't give you all this other pertinent information about the tube they like.

The thing that's missing when people compare the sonics of different rectifier tubes, typically in an amp, is that the B+ voltage changes due to the varying voltage drops of the different tubes. And running an amp at different B+ voltages will make the amp sound different. That's true whether you use tube or SS rectification. So the sonic differences can't be ascribed only to the choice of tubes.

I have yet to see anyone compare rectifier tubes in an amp whose B+ voltage has been adjusted to be the same with each rectifier type.

So the voltage drop specs of various rectifiers should be taken into account. But the actual voltage dropped will be less than the data sheets say in your case because they are based on the maximum operating conditions and your little preamp will not be running them that hard. I won't speculate as to how sonically sensitive your preamp might be to varying B+ voltage, it may not be as obvious as it is in an amplifier.

The specs show that the 5U4G and GA drop 44v and the 5U4GB drops 50v. The 5V4 drops 25v and 5AR4 only 17v. So your voltages will go up if you use them instead of a 5U4. The indirectly heated tube that's closest to the 5U4s is the 6087 which drops 50v. They are not real common, though, and might not be cheap. The directly heated 5Y3 drops 60v.

 

[Tom Bavis]

The voltage drop numbers are for rated current; will be much less at reduced current in a preamp. It's not directly proportional to current (like a resistor) so many data sheets will have a chart of voltage drop vs. current. Not that it helps a lot - it's peak current that matters, usually several times the load current. At the current used by a preamp, the 5V4 is likely a "forever" option too.

 

[nerdorama]

The Blue Velvet has glow tubes for shunt regulation so the current draw should be fairly constant.

 

[gadget73]

output voltage would be consistent, but current demands would depend on rectifier output voltage. Gas tubes are used as shunt regulators, so the more voltage they have to dump to ground, the more current flow the rectifier actually sees.

Blue Velvet Line Pre-Amplifier: A DIY Project by Dick Olsher (enjoythemusic.com)

5.gif (975×778) (enjoythemusic.com)

though quite honestly there is enough resistance between the output of the rectifier and the input of the gas tubes its not going to be different enough to really worry about.

 

[nerdorama]

If the glow tubes are working and configured correctly, there won't be any varying load on the power supply. That's the cool thing about a shunt regulator. They vary the current through them, within their range of capability, to keep the voltage constant. The current drawn from the power supply will be quite unchanging other than ripple current through the filter caps. The total current shared by the shunt and the load will be constant. The load draws more, the shunt draws less and vice versa. The series resistance upstream of the shunt is part of how it works and is what sets the total load current. Glow tubes have a limited current range so you have to design the circuit knowing the current range of the load to be able to determine if the glow tube has enough current range to regulate the voltage.

The 0A2 has a current range of 5-30mA. If you look at the BV schematic, the 2k resistor is dropping108 volts which is 54mA and the schematic lists the preamp draw as 40mA. This sets the quiescent draw of the glow tubes as 14mA which is approx the middle of the range so it can regulate about 10mA down or 15mA above and stay withing its regulating range. If the preamp stays withing the regulation range of the glow tubes the power supply will see a constant load.

I apologize for being long winded.
John

 

[gadget73]

if one rectifier output is say 25v higher than another type, the voltage drop across the series resistors will go up to end up at the same 300v of output. More volts / same resistance = more current. Its not a crazy amount, but its not zero either.

 

[nerdorama]

That's quite true. I guess I was assuming a given rectifier in my scenario. You were correct in your previous statements about it being a relatively small change given the high series resistances but if I was changing to a different rectifier I would want to recalculate the 2k resistor to keep the regulator current under control. Sorry that I missed your assumption of differing rectifiers.
John

 

[gadget73]

that was sort of keeping with the original question of using different rectifiers. I hadn't realized this was regulated at first, but since it is honestly that really just makes it matter that much less. The voltage fed to the unit won't change with the rectifier.

 

[FlaCharlie]

I also missed the fact that this preamp uses VR tubes.

But I still think the 5U4 is a poor choice, even if the only consideration is heater current. It will run cooler with a rectifier that only requires 2A of heater current. And a 5Y3 or 6087 will likely result in PS voltages that are closer to stock than a 5V4 or a 5AR4, although the difference might not be meaningful. But, as I see it, the closer you get to the stock voltage the less chance you would need to modify the circuit to stay within the range of the VR tubes.

 

[SwedishChef]

If the glow tubes are working and configured correctly, there won't be any varying load on the power supply. That's the cool thing about a shunt regulator. They vary the current through them, within their range of capability, to keep the voltage constant. The current drawn from the power supply will be quite unchanging other than ripple current through the filter caps. The total current shared by the shunt and the load will be constant. The load draws more, the shunt draws less and vice versa. The series resistance upstream of the shunt is part of how it works and is what sets the total load current. Glow tubes have a limited current range so you have to design the circuit knowing the current range of the load to be able to determine if the glow tube has enough current range to regulate the voltage.

The 0A2 has a current range of 5-30mA. If you look at the BV schematic, the 2k resistor is dropping108 volts which is 54mA and the schematic lists the preamp draw as 40mA. This sets the quiescent draw of the glow tubes as 14mA which is approx the middle of the range so it can regulate about 10mA down or 15mA above and stay withing its regulating range. If the preamp stays withing the regulation range of the glow tubes the power supply will see a constant load.

I apologize for being long winded.
John

No apology necessary. I'm learning so the more information that I get about rectifiers the better off I will be!
Tubes are so funny, one person on social media swears that 5U3C Svetlana black plates are his favorite. Another group member chimes in and said he didn't like them at all.
One person says use JJ tubes, another says they're terrible and junk.
Still feel like 5AR4 is the safer most stable upgrade of all these choices...

If I find out the transformer is capable of 3A it will be tempting to see what all the 5U4G fuss is about. If it ends up being 3A capable a WE274 Westinghouse would be interesting to try as well. But I'm not changing the preamp just to run these rectifier tubes. I'd live with a 5Z4 or 5AR4 before I started taking the transformer out to upgrade. The only "mod" that it will likely see is better capacitors down the road.

 

[SwedishChef]

I also missed the fact that this preamp uses VR tubes.

But I still think the 5U4 is a poor choice, even if the only consideration is heater current. It will run cooler with a rectifier that only requires 2A of heater current. And a 5Y3 or 6087 will likely result in PS voltages that are closer to stock than a 5V4 or a 5AR4, although the difference might not be meaningful. But, as I see it, the closer you get to the stock voltage the less chance you would need to modify the circuit to stay within the range of the VR tubes.

You're the second person to say 5U4 is a poor choice. Thank you for this information.

 

[FlaCharlie]

Tubes are so funny, one person on social media swears that 5U3C Svetlana black plates are his favorite. Another group member chimes in and said he didn't like them at all.
One person says use JJ tubes, another says they're terrible and junk.

Lots of "tube rollers" have drawers full of tubes, typically expensive ones, that they bought after reading something online. They try them and don't get the results they read about so they go into the drawer. The thing to remember is that tubes don't sound like anything on their own. They are only one element in the system.

Unless someone is using them in the same equipment as you are, with the same speakers and sources, and in a room with similar acoustics, then you shouldn't take specific recommendations that are based on "how they sound" very seriously.

This is especially true when the advice comes from a dealer who has a vested interest in selling you the tube. Typically, the best "holy grail" tubes are always the ones that the "boutique" dealer just happens to have in stock.

People hear things differently too, so even if they're both listening to the same system in the same room together they might not agree.

OTOH, comments about technical differences between tube types can be helpful.

Still feel like 5AR4 is the safer most stable upgrade of all these choices...

If I find out the transformer is capable of 3A it will be tempting to see what all the 5U4G fuss is about. If it ends up being 3A capable a WE274 Westinghouse would be interesting to try as well. But I'm not changing the preamp just to run these rectifier tubes. I'd live with a 5Z4 or 5AR4 before I started taking the transformer out to upgrade. The only "mod" that it will likely see is better capacitors down the road.

I don't know if specs for your power transformer are available. But the stock 5Z4P rectifier has a 2A heater, so that might be a clue as to what its 5v winding is comfortable with.

A 5AR4 will work fine but it's overkill because a preamp doesn't draw nearly as much current as a 5AR4 is capable of supplying. And even new production ones are not that cheap.

A 5Y3GT will be much cheaper and work just as well. If you want slow start the 6087 variant is also cheaper. Plenty of both on eBay. Even used ones are an option if they are American tubes that test strong and the test results are listed.

As for differences in sound, I would guess that different 6SN7s and coupling caps will have a far greater effect than different types of rectifiers. That's a far deeper rabbit hole.

You should also be aware that there are issues with many Chinese power transformers. Most of them seem to have primaries that are designed for 110v input from the wall. But wall voltage in the U.S. is typically between 120v and 125v. This pushes the secondary voltage and the heater voltages higher. So you should measure the heater voltages to make sure that it isn't too high as this can reduce the life of the tubes significantly, depending on just how high it is.