Rectifier Tubes-Pros and Cons

[basschops1528]

Hey guys,

I recently ordered some JJ's because they were 20% off and I snagged a 5Y3 for a champ build but now I'm not so sure a tube recto even has a useful purpose compared to a SS bridge except maybe some inrush limiting as the tube slowly conducts as it warms. Are there any pros to using one, opinion? Are there any other cons I may not know about? What do you guys think...

[hesamadman]

You really have to try it for yourself to answer that question. On paper, the SS rectifier is a bit more stable. As it can keep up with the fluctuating current. A tube rectifier, like they say, "sags" with a heavier current flow. It is noticeable by the ear. Is it by your ear? You'll have to A/B it to be sure. Use a DPDT switch and do both in your build. It will determine if you ever do it again. Will only add maybe an extra hour to your build.

[eleventeen]

I would say it is fully dependent upon what one person values over another. Some folks like the sag effect of (some) tube rectifiers; some would like their tubes to last longer; The inrush current thing is not a complete nothing, there could easily be a time when it blows a fuse or two and you are without amp for a gig. Arguably....that would just happen at some later date with a tube rectifier. But there is no question that a SS rectifier does slam the amp on startup.....whatever that means to you. Some folks believe that diodes impart a harsh barely perceptible noise....



When these amps originated, we did not have the internet to talk to thousands of other users and become obsessed over every possible nuance or to proclaim our superiority because we could detect this subtlety over someone who could not or who cared not. If we liked a particular artist and wanted to emulate their sound or went crazy over their playing...there weren't 217 different brands of guitars, 412 brands of amps, and 739 types of fuzzboxes back then. I blame it all on Les Paul!

[jjasilli]

I'm not so sure a tube recto even has a useful purpose compared to a SS bridge except maybe some inrush limiting as the tube slowly conducts as it warms.


The tube rectifier also has a "standby function" -- it keeps the tubes from drawing current until the filaments wram up a bit.

However, it also causes a voltage drop (and sag as stated above).  Here's a chart:  http://www.300guitars.com/articles/rectifier-tube-voltage-drop-chart/

The voltage drop should be figured into overall design.  A voltage drop from what?, one may ask.  From the 1.414 multiple of "pure rectification" without impedance.  If there is SS rectification, a tube's performance can be simulated by use of an appropriate value inductive power resistor.  Ohm's Law is used to determine the resistor value to produce the desired voltage drop.  Weber sells prepackaged units of this type.

[mresistor]

. I blame it all on Les Paul!

And we let Syd Barrett off the hook??

[tubeswell]

Hey guys,

I recently ordered some JJ's because they were 20% off and I snagged a 5Y3 for a champ build but now I'm not so sure a tube recto even has a useful purpose compared to a SS bridge except maybe some inrush limiting as the tube slowly conducts as it warms. Are there any pros to using one, opinion? Are there any other cons I may not know about? What do you guys think...

The 5Y3GT has that 'in-rush current limiting' characteristic because it has an indirectly heated cathode. A GZ34 is the same. However, for other tube rectifiers with directly heated cathodes, like the 5U4G, the startup surge is more instantaneous, and you want filter caps rated to take the maximum voltages that you get in these circuits.


To some extent, all rectifier tubes have a forward voltage drop, and a maximum amount of forward current that they can supply, which is more limited than an SS diode. These qualities can be useful to help design a circuit that sags (where louder signals draw more load on the PS when played hard and loud), but you can get similar (although not quite the same) effects with a sag resistor. This generally only works for push-pull amps. However, the bigger variation in forward voltage drop between different types of tube rectifiers does give a bit of extra versatility, in that swapping between types of rectifiers allows quick changes to be made to the B+ voltage.


It's generally a good idea to place SS diodes in series with the tube's plates and the HT winding to prevent catastrophic power supply failure in the event the the rectifier tube shorts. The 0.6V forward voltage drop per SS diode has negligible overall impact on the operation of amps using tube rectifiers (as tube rectifiers all have forward voltage drops in the order of magnitude of several tens of volts)

[basschops1528]

Tubeswell, would you happen to have a small drawing of how you would wire these diodes in series with the plate?

[Colas LeGrippa]

basschops, just put two diodes in series with the HT  ( the 2 red leads comin' out of the power tranny )  just before pins 4 and 6 of the recto tube ( one on each side ) and you're done.


Recently, I put back a 5Y3 in one of my builds, a small class A blues amplifier that I have designed entirely.
I had swapped it for a SS because I needed the rectifier tube in another amp. ( in french we have an expression : déshabiller Paul pour habiller Jean ).  For two years I've been looking at the empty  socket on the chassis, next to the power tube, asking for it's beloved tube. So, listening to my courage and my will to not leave female sockets alone    , I put back a 5Y3 ( not a JJ though , I hate them ), re-biased the thing and turned the amp on.


 WOOOOOOOOWWWWWWWW was my reaction when I started playing my guitar through it. The amp had become a musical instrument all of a sudden. Rich harmonics started to fill the room in a way that SS recto failed to do. If you need a tight responding amp, for heavy rock, you may need a SS rectifier, if you wanna save money, too. I can understand that a ss made of a couple of diodes cost  NOTHING  compare to a socket, tube, wiring and installation time and this is certainly one of the reason why commercial amplifier builders are using it.


Colas

[tubeswell]

Tubeswell, would you happen to have a small drawing of how you would wire these diodes in series with the plate?

A diode goes in series between each respective end of the PT's High-Tension ('HT') winding and the relevant rectifier tube socket pin. The diode's cathode (banded end) points to the rectifier tube's plate pins, and the other end points to the respective end of the HT winding. The SS diode's PIV rating is important. It should be 2.8x the peak voltage seen between each winding end and the CT (on 2-phase-rectifier HT windings). In amps with a 350-0-350VAC winding, this would be 1 x 1,000V 1A (1N4007) on each side of the HT winding (but Merlin Blencowe recommends a maximum of 290-0-290 - to allow for variations in mains VAC and transformer load regulation). In higher voltage amps, you could use 1.5kV or 2kV diodes or put 2 or more 1N4007 in series on each side. Try googling 'R.G. Keen's immortal amp mods, Premier Guitar'. Its number 1 in the series of articles that came out in the June, July, August and September 2008 magazine issues IIRC.

[traynor]

5Y3 is directly heated, 5V4 and 5AR4 are indirectly heated. 5V4 tubes are great to use if you don't have a standby switch and want your amps voltage to ramp up slowly.

[macula56]

The voltage drop should be figured into overall design.  A voltage drop from what?, one may ask.  From the 1.414 multiple of "pure rectification" without impedance.  If there is SS rectification, a tube's performance can be simulated by use of an appropriate value inductive power resistor.  Ohm's Law is used to determine the resistor value to produce the desired voltage drop.  Weber sells prepackaged units of this type.[/font]

If I have a PT with 300v legs I multiply that by 1.414 to get an idea of how much working voltage I will have with a SS rectifier. What do you multiply by when using a tube rectifier? Is there a chart for that as well?

[jjasilli]

The voltage drop should be figured into overall design.  A voltage drop from what?, one may ask.  From the 1.414 multiple of "pure rectification" without impedance.  If there is SS rectification, a tube's performance can be simulated by use of an appropriate value inductive power resistor.  Ohm's Law is used to determine the resistor value to produce the desired voltage drop.  Weber sells prepackaged units of this type.

If I have a PT with 300v legs I multiply that by 1.414 to get an idea of how much working voltage I will have with a SS rectifier. What do you multiply by when using a tube rectifier? Is there a chart for that as well?

Yes, once you measure or calculate the forward DC voltage from the SS rectifier, just use the voltage drop chart I posted earlier. Other charts are easy to google.  Also the rectifier tube spec sheets provide a multiplier to calculate forward Dc voltage.  For SS it's the full 1.414.  For a particular rectifier tube it might be 1.1, or .9, e.g.


(Note that your PT's 300VAC rating is probably stated for the condition when the PT is feeding a circuit with that tranny's stated mA draw. If your amp has a different mA draw, the PT's secondary voltage will be commensurately higher or lower.  Whatever your measured secondary voltage is unloaded, figure a 10 - 15% drop from there when loaded.  See, Jack Darr's Electric Guitar Amplifier Handbook.)

Tubeswell, would you happen to have a small drawing of how you would wire these diodes in series with the plate?

A diode goes in series between each respective end of the PT's High-Tension ('HT') winding and the relevant rectifier tube socket pin. The diode's cathode (banded end) points to the rectifier tube's plate pins, and the other end points to the respective end of the HT winding. The SS diode's PIV rating is important. It should be 2.8x the peak voltage seen between each winding end and the CT (on 2-phase-rectifier HT windings). In amps with a 350-0-350VAC winding, this would be 1 x 1,000V 1A (1N4007) on each side of the HT winding (but Merlin Blencowe recommends a maximum of 290-0-290 - to allow for variations in mains VAC and transformer load regulation). In higher voltage amps, you could use 1.5kV or 2kV diodes or put 2 or more 1N4007 in series on each side. Try googling 'R.G. Keen's immortal amp mods, Premier Guitar'. Its number 1 in the series of articles that came out in the June, July, August and September 2008 magazine issues IIRC.

My modded VibroChamp has the circuit.  Schematic below. 

[Paul1453]

Here is an excellent resource document that Tubenit originally provided.   

[HotBluePlates]

... If I have a PT with 300v legs I multiply that by 1.414 to get an idea of how much working voltage I will have with a SS rectifier. What do you multiply by when using a tube rectifier? Is there a chart for that as well?

"1.414" is √2 and is the factor for converting the RMS value of a sine wave to the peak value. We assume the incoming a.c. is a sine wave and ignore the voltage drop of solid-state devices because the 0.7-1.4v drop is both consistent and usually insignificant when hundreds of volts are rectified.

But a tube rectifier has significant apparent series resistance, and the voltage drop is not a convenient, fixed ratio of applied sine voltage. It depends on circuit current draw and filter cap size, as well as characteristics of the PT used.

If you need to guess ahead of an actual build download a copy of RDH4 here and flip to the chapter on Rectification. Or use the Duncan Power Supply Designer after downloading the appropriate tube rectifier models and plug in what you know.

The other ratios given for certain tubes are based on observations from specific amps. If you deviate too far from the circuit conditions of the amps observed, the actual rectified voltage will be different than that predicted by the ratio. In all cases, you should plan for filter caps to be rated for at least PT RMS voltage * 1.414 (and possibly a bit more).

[jjasilli]

Well put.  There are down & dirty general rules of thumb which are useful, but are better used with a deeper understanding of the subject matter.

[macula56]

thanks  HBP and jjasilli.

[Ed_Chambley]

Normally I will allow for a place for the tube rectifier, even if I use diodes.  If cutting the chassis i mean.  I may not install a tube socket in a Marshall type build, but could go back and do it.


 Sure you can achieve sag using a resistor, but varying voltages as Tubeswell mentioned is a bonus.  For instance, WEBER makes a copper topped SS rectifier tube and they simply use diodes and 1 10 watt resistors to create the voltage drop of a tube.


With an empty tube base I will install diodes and fill it level with hot glue and have a SS rectifier for a couple bucks.  These are backups for tubes.  I think the biggest benefit of the tube is flexibility, but planning for one always makes you fold a larger chassis and a larger chassis is always good to me.

[Mike_J]

Ed mentioned to me that he liked tube plate voltages of 360VDC for a Deluxe Reverb style build. I was building a Deluxe Reverb style build with a PT that has 300-0-300 and 330-0-330 secondary taps. The only way I could get 360VDC is to use the 300 volt taps and a 5U4GB rectifier. Like the tone very much. With a 5ar4 rectifier voltage is around 390 volts and with a solid state plug in the rectifier socket I get about 420VDC which is what the Deluxe Reverb schematic calls for. The amp is tighter at 420VDC but for classic rock and blues the 360VDC sounds better to my ears. Either of these settings can be useful however. Just a matter of what you are trying to accomplish with your amp.


Thanks
Mike

[basschops1528]

So for the most art, as long as you don't exceed the rated voltage AND current, you can use any recto tube?

[eleventeen]

"For the most part", yes. The common ones, GZ34, 5Y3, 5U4, 5V4, 5R4, 6087, and that Bendix ultra-slow warmup one whose # I can't recall are all "pin compatible" and will work interchangeably in a given rectifier socket.  And there are probably 10 more, these are just the most common types.


Some use 2 amp filaments, some use 3 amp filaments.


If I was experimenting with a light duty power supply, I could use any one of the above and not care.


They all have different voltage drops.


The most critical thing is to not have too many ufds in the first filter cap. That can cause a big current spike and whack the tube to destruction. On the first turn on of a new build, you NEVER want to have your brand new GZ34 in there.....you want a cheap old 5Y3 in case something blows up. It is also useful to use a 5Y3 in an amp designed for a GZ34 because it will chop maybe 25-30 volts off the B+, if that is of concern. I happen to like 5Y3s just because I once bot a garage full of tubes and have 3 lifetime's supply. 5U4's are good if you get used ones of out dead TV sets.

[basschops1528]

Yeah, what's this I hear about Russian GZ34s being poor? And why do they fail with voltage spikes vs other types?

[Mike_J]

So for the most art, as long as you don't exceed the rated voltage AND current, you can use any recto tube?

Add the uF rating of the first power cap to that as mentioned by eleventeen. As I recall you shouldn't go over 33uF when using a 5Y3, 50uF for 5ar4s and 5U4GBs. Have seen amps with over 200uF when using solid state rectification.


Thanks
Mike

[HotBluePlates]

... As I recall you shouldn't go over 33uF when using a 5Y3, 50uF for 5ar4s and 5U4GBs. ...

It's not that simple. Go back to the link I posted in my reply, and read the chapter on Rectification.

Take a look at this 5Y3GT data sheet. Look at the 1st page; this rectifier is designed to supply 125mAdc, but has a rating for "Transient Peak Plate Current per Plate" of 2.5A.

That transient current is briefly pulled every cycle to recharge the main filter cap. The amount of current depends on the supply voltage, the size of the filter cap, how much current is drawn away from the cap when the rectifier is not charging it, and how much resistance there is in the circuit made up of the wall outlet, PT, rectifier and filter cap. Charging time as a result of all those other factors plays a role.

So it's hard to say exactly what size filter cap any given rectifier can support (that book chapter will explain the process of figuring it out). There are cases where a filter cap used in a commercial amp seems "too large" for the given rectifier, but the manufacturer adds series resistance to keep the peak plate current within the tube's specs.

[basschops1528]

Hey Eleventeen, what's the deal with the GZ34? Why can't you fire up an amp with it and instead use a 5Y3?   Can you put safety diodes in with any type of rectifier?

[drgonzonm]

IMO If someone is installing a tube rectifier to avoid installing a standby switch, its dollar foolish, and penny wise.

My preference, is tube rectification, carbon resistors, standby switches, chokes, and tolex with SS protection for no other reason, (and its not a good one), those slide rule designers didn't have decent SS components, and why risk $$$ because of a component failure. 

And while I am expressing my opinion, I would prefer to use a choke rather than a resistor for my voltage dropping.  (I made an adapter for the three point hitch on my tractor so I can lug the amps around.  )

 

[uki]

Check out this link:
http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1

[Paul1453]

IMO If someone is installing a tube rectifier to avoid installing a standby switch, its dollar foolish, and penny wise.

My preference, is tube rectification, carbon resistors, standby switches, chokes, and tolex with SS protection for no other reason, (and its not a good one), those slide rule designers didn't have decent SS components, and why risk $$$ because of a component failure. 

And while I am expressing my opinion, I would prefer to use a choke rather than a resistor for my voltage dropping.  (I made an adapter for the three point hitch on my tractor so I can lug the amps around.  )

I'm mostly of the same opinion as yours.

If you are using a tube rectifier, and especially a gradual warm up rectifier, I prefer not to use a standby switch.
I will use them with a SS rectifier, if I have the space for the switch.
If there is no space for the switch, I wouldn't sweat not having one.
I'm not convinced they are needed, or that leaving your amp on Standby for too long won't damage your tubes.
If I want to silence the amp, it seems easier to me to just turn the volume on my guitar to 0 instead of walking to the amp and flipping a switch.

Adding protective diodes to your tube rectifier seems like a no brainer to me.
Now if your tube rectifier fails short, you don't blow up your amp.
A couple of diodes only costs pennies.
A new PT could be $100 or more.  Always add those diodes, IMO.

Chokes are something I also prefer using.
They are heavy, and much more expensive than a resistor, but still worth it to me.
Their filtering and storage of some electrical energy cannot be replicated exactly by an RC filter.
They definitely have an effect on the PS, which effects the sound, when you push your amp hard.