Tube rectification in bass amps?

[Alper Yilmaz]

This might have been covered in another post, but I could not find one. Sorry, if it was discussed before...

I wonder why tube rectification is not used in bass amps in general. I am not sure if there are any exceptions, but when I look at Ampegs (current production) for instance, I see that the SVT and Portaflex series are all SS-rectified.

The reason I am asking this is purely out of curiosity, but I have a few different hi-fi systems at home and two of them (built by Decware) use tube rectification. Interestingly, in these systems, the rectifier tubes seem to make the most sonic difference, particularly when it comes to the tightness of bass and overall balance of the amp. Input and output tubes have their signature sounds as well, yet less so than the rectifier tubes (again, in my systems).

In a live application, it might be more difficult to hear and tell, but would tube rectification affect the sound that much in bass amplification? Or is there a reason for not having tube rectification in bass amplification (I know in guitar amplification quite a few amps use tube rectification)?

 

[Wasnex]

This might have been covered in another post, but I could not find one. Sorry, if it was discussed before...

I wonder why tube rectification is not used in bass amps in general. I am not sure if there are any exceptions, but when I look at Ampegs (current production) for instance, I see that the SVT and Portaflex series are all SS-rectified.

The reason I am asking this is purely out of curiosity, but I have a few different hi-fi systems at home and two of them (built by Decware) use tube rectification. Interestingly, in these systems, the rectifier tubes seem to make the most sonic difference, particularly when it comes to the tightness of bass and overall balance of the amp. Input and output tubes have their signature sounds as well, yet less so than the rectifier tubes (again, in my systems).

In a live application, it might be more difficult to hear and tell, but would tube rectification affect the sound that much in bass amplification? Or is there a reason for not having tube rectification in bass amplification (I know in guitar amplification quite a few amps use tube rectification)?

The main issue is tube rectifiers are not capable of providing enough current for high-powered amps. The Sunn 2000S had two tube rectifiers and made about 120W. the Sunn 350B is pretty much a 2000S with a solid state rectifier. Some say the 350B made 130W, and some say it made 150W. I haven't played these amps so I can't tell you how much the sound and feel changes.

I own a Matchless Thunderchief that is switchable between solid state and tube rectifiers. It has a pair of Svetlana 5C3S rectifiers which are supposed to be equivalent to 5U4G. Max anode current is 225mA per tube and the rectifer also drops off quite a bit of voltage due to it's internal resistance. This internal resistance causes more sag in the power supply so the amp feels a bit more compressed. In solid state mode the HT voltage is 540V and in tube rectifier mode the HT votage is 500V. Obviously the amp makes more power in solid state mode. Actually the tube rectifier mode is labeled "Half Power."

The tone and feel is slightly different in the different modes as well, but this can partially be attributed to optimal bias levels. The amp only has one bias circuit and the factory setup is to bias it for the solid state setting. Then, when you switch to tube rectifier mode the bias is too cold.

I did an experiment where I optimized the bias in the tube rectifier mode. I think the amp sounds better with the bias optimized in half power but this entails giving up some headroom due to the lower operating voltage. Also, it possible the preamp works better with lower voltage, so I don't think this is really conclusive that tube rectifiers are better.

The Thunderchief was touted as a 200W amp, but IMHO it's more like 100W. It's a great sounding head, but it's the least powerful 200W head in my collection.

 

[Alper Yilmaz]

Makes sense... The hi-fi amps that I have are 2.3W/ch. and 6.0W/ch., respectively!

Thanks for the detailed response Wasnex...

The main issue is tube rectifiers are not capable of providing enough current for high-powered amps.

 

[teemuk]

What was said. Due to high internal impedance of tube rectifiers the power supply voltage will "sag" considerably under loading and this will in turn effect overall "tightness" and "punch". Folks are generally not overly fond of bass amps with loose and flubby response that fart out when one plucks the strings. What works in guitar amps does not neccessarily translate to bass amplification. In same manner, bass amplifiers generally feature quite high damping factors (that enhance overall "tightness"), whereas in guitar amplification overall preference leans towards lower damping factors and "tubey" response it can provide while driving reactive loads.

...And true: tube rectifying could be made more efficient with several parallel-connected rectifiers, but it's hardly cost-efficient given that equal and better performance can be achieved with solid-state diodes that cost just few cents. Internal impedance of tube rectifier, in turn, is easy to mimick with a cheap power resistor connected in series with the rectifier (just in case "spongy" characteristics happen to be preferred).

 

[beans-on-toast]

The rectifier is not directly in the signal path so a solid state rectifier in a tube amp does not mean that it isn’t an “all tube” amp. As described, the tube rectifier is a big component of an amplifier’s sag. Sag results in a loss of headroom and eventually distortion.

 

[agedhorse]

Tube rectifiers were the very first part replaced by solid state (selenium) rectifier when they were available because for many applications (including bass amps) they provided a clear benefit to performance.

Very few players would prefer a tube rectifier over a solid state (now silicon) rectifier in a bass amp.

 

[BogeyBass]

If you look at the more common highest Current Tube rectifiers, it still takes about 2 of them to support 100/120 watt amps.

Once you try to go above 150 watts the current capability is not there.

Another problem is tube rectifiers do not like high value capacitors, your limited to max specified capacitance
to reduce power supply ripple. With solid state rectifiers you can reduce ripple/hum more effectively.

You can increase capacitance and improve voltage regulation/ reduce ripple with a
tube rectifier. By adding a inductor to the power supply.
Additional capacitors can be added after the inductor . But its relatively rare to see inductors in the power
supply with Musical instrument amps, Raises cost and weight.
You typically only see small inductors for preamp tubes, not the main power supply.
High current inductors are very heavy and add more cost.

Another problem is Tube rectifiers require heater voltage as well, and to run 2 rectifiers.
Requires a very high current low voltage winding. Since the low voltage winding is also needed for
preamp tubes. Running tube rectifiers and preamp tubes. The low current windings eats up alot of space
In the Power transformer. Likewise low current transformers add a lot of weight and cost

Another issue with tube rectifiers is a 20 to 30 volt voltage drop to the power supply.
Compared to a solid state voltage drop of 0.7 to 1.2 volts per diode.

There is no improvement in sound with a tube rec as described in the OP.
A good performing tube amp is in the transformers.
Current/voltage from the power transformer.
And the quality of the output transformer, mainly a higher cost core, windings, increased interleaving etc etc. to improve the ability to reproduce lower frequency

Often earlier amps with tube Rectifiers were modified to solid state. Your would increase voltage.
And tend to get little more power/ less sponge at full power hence more voltage/ more current. Basically removing the tube rec, plate voltage increased.

All in all Tube recs are " magical" for guitar players since the voltage sags even more under high load.
So the power amp will distort faster.
Being around a zillion high gain Mesa Dual Rectifier Amps in the 90s and Up. There was a option to turn the tube rec
off and run a solid state Rectifier. Labeled "Spongy" and "Bold".
Pretty much 90% of guitar players set it to Bold setting running the solid state rec. And the notorious tube recs
just sat there doing nothing. The main love with the amp was the high gain preamp.

 

[JimmyM]

The rectifier is not directly in the signal path so a solid state rectifier in a tube amp does not mean that it isn’t an “all tube” amp.

Thank you! Of all the anti-tube amp arguments on here, saying that a tube amp isn't a tube amp because it doesn't have a tube rectifier is probably the dumbest. I mean, they're all dumb because way too many tube amp haters are so very emotionally invested in hating them that they have to convince everyone in the world of how their hate is legit and not just a bunch of passive aggressive gear acceptance issues. But that one is especially dumb.

 

[Passinwind]

Thank you! Of all the anti-tube amp arguments on here, saying that a tube amp isn't a tube amp because it doesn't have a tube rectifier is probably the dumbest. I mean, they're all dumb because way too many tube amp haters are so very emotionally invested in hating them that they have to convince everyone in the world of how their hate is legit and not just a bunch of passive aggressive gear acceptance issues. But that one is especially dumb.

I love me some tubes, except when I don't, but "all tube" is just flat out useless snobbery IMO. Just say no!

 

[JimmyM]

I love me some tubes, except when I don't, but "all tube" is just flat out useless snobbery IMO. Just say no!

HAHAHAHA!!! Good one, Charlie!

 

[BogeyBass]

Tubes are cool regardless.
I think there is a extra romance and cool factor to the glowing tube rectifier.
Regardless the whole Quasi soft sort slow warm up thing is there with a tube Rec.

Sound quality with no distortion is not effected. The rectifier just makes DC voltage
you dont hear DC voltages. Technically it removes 30 volts of overhead.
to the plate voltage
Tube Rec is " audible" at high gains. But your not hearing the tube.
Its power amp distortion kicks in early.

Anyhoo point is there is always a certain Romance to tubes.
The only way I can describe it.
Tube Rec just looks cool.

If you wanted a 6V6 pair or 6L6 pair for 20/30 watts.
Tube Rec has its uses for Guitar Distortion.
Or yes a table top vacuum tube amplifier for
music at home. The tube Rec just looks cooler, sounds like
a cool feature.

Far as the real world, solid state rectification
and solid state diodes for AM radio detection/ demodulation.
Had a significant reduction in weight, cost , increased performance, etc etc

 

[Alper Yilmaz]

Thanks folks, this is a very informative discussion!

 

[Alper Yilmaz]

Thanks for the detailed explanation BogeyBass.

As per your comment below, I was not trying to say tube rectification would improve sound over SS, but in my Decware amps (www.decware.com), different rectifier tubes give different signature sounds. One of the amps, for instance, is compatible with 5U4, 5Y3, GZ32, GZ34, 274B, Type 80, and quite a few more rectifier tubes. They all sound different given all else constant.

There is no improvement in sound with a tube rec as described in the OP.
A good performing tube amp is in the transformers.
Current/voltage from the power transformer.
And the quality of the output transformer, mainly a higher cost core, windings, increased interleaving etc etc. to improve the ability to reproduce lower frequency

 

[Iristone]

Come to think about it, even the venerable Marshall Super Bass that people like for overdriven tone but has limited clean headroom, had solid-state rectifiers to make it less quiet or distorted. A tube-rectified one would likely be ... Even quieter.

 

[JimmyM]

Thanks for the detailed explanation BogeyBass.

As per your comment below, I was not trying to say tube rectification would improve sound over SS, but in my Decware amps (www.decware.com), different rectifier tubes give different signature sounds. One of the amps, for instance, is compatible with 5U4, 5Y3, GZ32, GZ34, 274B, Type 80, and quite a few more rectifier tubes. They all sound different given all else constant.

Yeah, I believe that. But I noticed that their 60 and 40w amps don't have rec tubes. The highest wattage you can get one is 25w. So you won't be finding them in SVT's any time soon, either.

On the bright side, thanks to Decware, I found out that the 6N1P-EV's they use go for $4! As a REDDI owner, that makes me happy. Might have to try one...probably would if not for having a bunch of 6N1P's already

Come to think of it, you have a REDDI, don't you? Ever try one in it?

 

[micguy]

Tube rectifier's use power to do their job, and give you less power at the output of the power supply for the rest of the circuit to use. They're in general less reliable - some of the early solid state replacements in Fender amps were not so reliable, but things are now considerably better in terms of solid state diodes - they're clearly better than tubes at this point (and have been for decades).

If you want your amp with solid state rectifiers to sound like it has a tube rectifier when clipping, you can add resistors in the power path, and get the "spongy" supply of a tube rectifier, but to my knowledge, noone does that, as it mostly just wastes power.

 

[Alper Yilmaz]

Yes, I did, Jimmy. That’s some of the best 6N1P tubes in the market. I also have thought about trying 6N2P and 6N5P in my REDDI, but I was too lazy to try as the 6N1P provided by Decware is already so good, and so much better than the stock Sovtek that on the unit.

 

[JimmyM]

Yes, I did, Jimmy. That’s some of the best 6N1P tubes in the market. I also have thought about trying 6N2P and 6N5P in my REDDI, but I was too lazy to try as the 6N1P provided by Decware is already so good, and so much better than the stock Sovtek that on the unit.

Dang, think I might have to pop for one or two. Thx Alper!

 

[Killing Floor]

Great thread. I love the option of tubey goodness. Who would hate on tube amps?
But to be fair I think we bassists care and obsess a lot more about our tone than others. I wonder if non-musicians notice? But regardless, a little bite is good for you.

 

[wmhill]

I picked up a '78 Fender Vibrolux (guitar amp) this summer and switched out the rectifier tube
for one of the cool little solid-state rectifiers that plugs right into the tube socket. I really appreciate
how it tightens up the tone and smooths out the power. And this is a 40-watt amp, I can't imagine
how gnarly a big tube powered bass amp would be if it was tube rectified.