• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Rectifiers do sound different

Some hints:
-some rectifiers have almost the same internal resistance, hence almost no variation, less than 1% in the rectified voltage, at least in the condition we tested them lately
-we test them in a class A amplifier, so the sag theory doesn't apply.
-different brands, same tube, no measured voltage variations, but different tembral signatures.

I don't fully understand it yet as well. But it works.

Do you consider placebo effect or a psychological bias as an explanation?

That's a genuine question as to whether someone who hears a difference but can't explain it rejects explanations that say the result they're trying to explain doesn't exist. Or whether their quest for an explanation includes placebo too.
 
So, what would one measure for?
Loaded DC voltage output doesn't seem conclusive to me. ...
I do not claim to posses a definitive answer. Since you observe a difference in IMD, I would suspect a difference in THD as well.

If no distortion analyzer is available, a soundcard interface is not terribly difficult to make. A software called DiAna can do FFT to produce spectrum of harmonic distortion and plot distortion residual waveform to show overall shape and phase of distortion relative to fundamental. A clear noticeable difference should produce measured difference in spectrum, shape and phase of distortion not terribly difficult to spot.

I have also seen differences in response to square wave signal input on amplifiers but not sure the trick can show enough visible difference in this case. You may want to try several frequencies to be sure.

Let's discuss other measurements if both tricks fail to show any difference.
 
Do you consider placebo effect or a psychological bias as an explanation?

I believe placebo effect should occur where there is psychological bias, such as saying to the whole group "this rectifier is expensive ; better ; new ; etc". Usually when we listen to components swapping in groups, we tend to neglect what is happening on the system, just enjoying the moment and having some chat with others. When the system owner is ready with the swap, we listen to a few tenths of seconds to test tracks, note the differences if there were any, and wait for the next swap.
IMHO, the less focused is the person being tested on the system, the better the hearing. Too much focus can put some strain on the nervous system and that results in worse sound hearing capabilities. Just observations.
 
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One of the first things for tube rectifiers is to split the hating from HV transformer. Heaters should be from the additional power transformer. Close to the tube (under). If it is posibile connect to heaters within the transformer wire. In the same time that is isolated Stand-By...
If we want to examine real tube rectifiers power transformer for the HV also has to be very good. Just for HV nothing else. Another thing is that Inductions of primary of all power trafos has to be 1T or lower.
The correction 2 x R to anode is option depending of Rdc of transformer. How to treat you can find in some datasheet (as I am remember well in 6X4 pdf exist...)
...
Take notice that gas rectifiers usually have lower voltage drop than vacuum rect.
cheers
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And Yes I like tube rectifier more than other types. Even for diskrete devices :)
 
Well, why do you suggest separate heater transformers ? I actually do have them, but as well transformers which have both...I never considered that this would make a sound difference ?

Or is it to heat first the rectifier and have HV 10sec. later which may help to save rectifier life ?

Mercury...this is actually on my list for next weekend...very curious how this sounds compared to normal stuff like gz34/5r4g etc...any experience / sound impressions to share ?
 
Well, why do you suggest separate heater transformers ? I actually do have them, but as well transformers which have both...I never considered that this would make a sound difference ?

Or is it to heat first the rectifier and have HV 10sec. later which may help to save rectifier life ?

Mercury...this is actually on my list for next weekend...very curious how this sounds compared to normal stuff like gz34/5r4g etc...any experience / sound impressions to share ?
The MV rectifier is best to use seperate 5v transformer for filament. That way you can get full evaporation of the HG inside before apply HV to the plates. A drop of HG in the right spot, then 2kv applied can cause some interesting pyrotechnics inside the tube. ;)
 
Well, why do you suggest separate heater transformers ? I actually do have them, but as well transformers which have both...I never considered that this would make a sound difference ?

Or is it to heat first the rectifier and have HV 10sec. later which may help to save rectifier life ?

Mercury...this is actually on my list for next weekend...very curious how this sounds compared to normal stuff like gz34/5r4g etc...any experience / sound impressions to share ?
I had AX50 on a pair of Philips EL6420 amp.
all I can say is that it's beautiful to watch, to the extent that I did not try other instead on these amps ...
however, I can say that the 5c3s are by far the best I have in my possession compared to my 5u4gb (rca, ultron and EH)
 
I will do the comparison this weekend...very curious...the 5c3s, I got many of them...very nice ones from the 50s with black plates etc.

Yes, they do sound impressive first...but later you can spot there sound, which is more treble-pronounced, sort of dry, not very full tone...some would say, typical russian sound.

I prefer the RCA 5R4gys, The EML274b etc...but still searching for the chameleon which gives me tone/vibration, dynamics, and resolution...

...all of that is in my experience dependands on the individual built. I use a different transformer than you do...different chokes and PSU etcetc. so my impressions are only valid in my setting I guess, yours will ne different for a good reason.
 
Why?


Why?


Why?

When we have heating, high voltage and maybe some other windings on the same transformer, they have capacitive coupling. Voltages are high, and difference is huge, proportion to coupling. Also there is a sort of "mixing" with step up and step down transformation from the same primary...
And the question of stand by switch could be significant in this common case.
Because Stand by switch has to turn on/off very high voltages directly.
...
With separate stepup and step down transformers, we can achieve better and more appropriate wiring too. Because of shorter wiring, heaters from DH tubes could be conn. directly from the socket to transformer secondary and Cathode is still there on 5-10cm.
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NOT like 1m back and forth to the single power transformer. That is also the case for the Rectifier tube...
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I tried it and it is very good. Decreasing hum and noise. Increasing stability. And safety. I like presence of Stand By option. For instance if You set time controlled stand by with separate HV xformer and others, You can turn on 1st heating and with switching off, turning off 1st HV transformer, and later when HV spend by the device turn off rect and other tubes. In that case We can avoid bleeder resistors and save some tube extra "life" :)
 
I had AX50 on a pair of Philips EL6420 amp.
all I can say is that it's beautiful to watch, to the extent that I did not try other instead on these amps ...
however, I can say that the 5c3s are by far the best I have in my possession compared to my 5u4gb (rca, ultron and EH)

I have very good mood with FIVRE 5U4GB (compared to the GE, RCA, and other) I didn't try Russian version, but i will - thanks for the tip.
 
me too but the price cools my desires to try

Indeed, I have a luck to collect some pieces decades ago...
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And one more rectifier can be very good, the same base, 4V/2.8A like AX50 (not sure about pins, and probably diff in voltage drop...), but common vacuum U18/20. Beautiful :)
I didn't tried yet but I have to.
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I like AX50 very much, and some of the friends consider AX50 no1 rect in their amps.
 
When we have heating, high voltage and maybe some other windings on the same transformer, they have capacitive coupling. Voltages are high, and difference is huge, proportion to coupling. Also there is a sort of "mixing" with step up and step down transformation from the same primary...
That really isn't a technical explanation - more like a wave in the direction that there may be some technical issue.

The coupled secondary windings can cause rectification glitches to transfer from the HV secondary winding to heater winding, and can show up as noise entering preamp tubes that are in a configuration that doesn't adequately manage heater hum/noise. In some instances that preamp hum/noise can be avoided by using a tuned humdinger. HV secondary windings with silicon diode rectifiers are more prone due to the higher dI/dt they induce, which may be avoidable using Quasimodo style snubbering. HV windings with relatively low resistance, and relatively high leakage inductance would also be more prone, as well as rectifier tubes with relatively low on-voltage.
...
With separate stepup and step down transformers, we can achieve better and more appropriate wiring too. Because of shorter wiring, heaters from DH tubes could be conn. directly from the socket to transformer secondary and Cathode is still there on 5-10cm.
.
NOT like 1m back and forth to the single power transformer. That is also the case for the Rectifier tube...
.
That is likely your particular concern with amplifier part layout, rather than a general situation that most others find.
I tried it and it is very good. Decreasing hum and noise. Increasing stability. And safety.
That may well be for your particular amp builds, but I'd suggest that huge numbers of well made valve amps show that separate transformers are not needed for their application.
I like presence of Stand By option. For instance if You set time controlled stand by with separate HV xformer and others, You can turn on 1st heating and with switching off, turning off 1st HV transformer, and later when HV spend by the device turn off rect and other tubes. In that case We can avoid bleeder resistors and save some tube extra "life" :)
It would be sad if your capacitors did not have bleeder resistors from a safety perspective. And from a 'life' perspective, I can't see how that could be a tangible outcome - are you referring to a rectifier tube having to operate at say 0.1% higher peak current becasue of a bleeder being used, compared to no bleeder?
 
Bleeder resistors are required on big amplifiers.

On smaller amps I find that a dedicated bleeder isn't required due to tubes drawing much of the charge after power is cut and the residual charge lasting not very long due to other places where it can bleed, some is required but not a dedicated bleeder resistor.

My big amps have many bleeder resistors and the capacitor bank keep the voltage quite high for a few minutes after shut down, I find big tubes such as KT150 shuts off more abruptly after heater is off than smaller tubes which conducts even at low temps.

It can be also due to the voltage , a 700V cap will maybe get down to 100V after shut down, while a 250V will drop to 35V which is almost safe :)
 
That really isn't a technical explanation - more like a wave in the direction that there may be some technical issue.

The coupled secondary windings can cause rectification glitches to transfer from the HV secondary winding to heater winding, and can show up as noise entering preamp tubes that are in a configuration that doesn't adequately manage heater hum/noise. In some instances that preamp hum/noise can be avoided by using a tuned humdinger. HV secondary windings with silicon diode rectifiers are more prone due to the higher dI/dt they induce, which may be avoidable using Quasimodo style snubbering. HV windings with relatively low resistance, and relatively high leakage inductance would also be more prone, as well as rectifier tubes with relatively low on-voltage.
...

That is likely your particular concern with amplifier part layout, rather than a general situation that most others find.

That may well be for your particular amp builds, but I'd suggest that huge numbers of well made valve amps show that separate transformers are not needed for their application.

It would be sad if your capacitors did not have bleeder resistors from a safety perspective. And from a 'life' perspective, I can't see how that could be a tangible outcome - are you referring to a rectifier tube having to operate at say 0.1% higher peak current becasue of a bleeder being used, compared to no bleeder?

That is exactly technical issue. Try to look at the simple formula about capacitance. Directly proportional to the potential difference, and insulation thickness... Add to this same core where the transformation acting.
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Please take a look at the practical design employing DHT with long center tap as cathode. this is the double distance from tube to the transformer and back near the tube. It could be 1m long in common chassis and up to 2m or more in "designs" with physical separate PS unit. And 3 wires included per tube. As well as for rectifier tube.
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Bleeder resistor is shunt component to the power line. But not as the proper shunt current value that should be more than 100% of device consumption, but usually much lower. And I found that degrading the sound in preamps. So it will give the same sound signature in input stages of amplifier.
It could be included in PS to discharge HV, but after power off, with some relay.
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Separate transformers are NOT needed off course, but if You want the device differs from 99.9% designs and make some improvements with not much additional money there is a way.
...
Shubber is welcome to the secondaries.
 
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Bleeder resistors are required on big amplifiers.

On smaller amps I find that a dedicated bleeder isn't required due to tubes drawing much of the charge after power is cut and the residual charge lasting not very long due to other places where it can bleed, some is required but not a dedicated bleeder resistor.

My big amps have many bleeder resistors and the capacitor bank keep the voltage quite high for a few minutes after shut down, I find big tubes such as KT150 shuts off more abruptly after heater is off than smaller tubes which conducts even at low temps.

It can be also due to the voltage , a 700V cap will maybe get down to 100V after shut down, while a 250V will drop to 35V which is almost safe :)

Bleeder Rs are needed but only to turn on with power HV off. Relay switch from ground end of bleeder to ground.