SET amp owners thread

[SVS]

Not the ones I've seen. The Russian variants have greater voltage drops and so respond more dramatically to changes in the AC line voltage. The resulting lower B+ corresponds directly to reduced output power and altered operating point, which alters the distortion of the audio circuit. I can't think of why that would not be audible- harmonics after all are what make up the sound of musical instruments.

Everything happens the other way around. The new Russian 5U4G with the Sovtek brand gave a voltage of 420V, and a similar used RCA only 380V. But the sound from the RCA was much better. 5U4G Sovtek is the same Soviet 5?3?.

 

[Atmasphere]

Same old tune. As @SVS said, our ears tell us different rectifiers can sound different. That’s certainly true in my experience and it’s not just due to voltage drop. I don’t know why there is such resistance on this. Is there any doubt signal tubes that measure the same sound different? Everything matters. But as I have said a number of times, for those who think rectifiers of the same type sound the same, that’s fine, just leave the vintage NOS tubes for the rest of us.

I didn't say what you are suggesting here. First off just to be clear, I've never found a single tube that ever measured the same as another! They are always different, even if made on the same assembly line on the same day. I'm not contesting that different rectifiers sound different. They do!
But if you look at the Voltage they produce you get the answer:

Everything happens the other way around. The new Russian 5U4G with the Sovtek brand gave a voltage of 420V, and a similar used RCA only 380V. But the sound from the RCA was much better. 5U4G Sovtek is the same Soviet 5?3?.

If there is an assumption that with higher Voltage the amp will sound better, then its time to dash it; obviously that is incorrect. The amp will sound its best when the circuit is operating at the best operating points. The big influence is likely the operating point of the power tube, since most DHTs have a very low mu (and are thus more susceptible to B+ variation than higher mu tubes as might be found in the driver/Voltage amplifier section). A 40V difference is going to put the power tube off its operating point and distortion will rise. You stand a good chance, depending on the tube, of also cooking it.

Its the same as if you underbias or over-bias the tube- once you are off the ideal point, on either side distortion rises. You can hear this distortion as coloration and loss of detail since distortion obscures detail and distortion is interpreted by the ear as tonality. Its audible.

I don't know why this should be mysterious; guitar players have been tinkering with this phenomena for years now, since its possible to easily vary the power supply voltage with modern semiconductors, to mimic failing capacitors and weak rectifiers, with a twist of a knob for that 'blues sound'.

 

[morricab]

Everything happens the other way around. The new Russian 5U4G with the Sovtek brand gave a voltage of 420V, and a similar used RCA only 380V. But the sound from the RCA was much better. 5U4G Sovtek is the same Soviet 5?3?.

I have 1960s winged “C” NOS tubes. They are branded 5?3C and are military (stamped OTK).

 

[Salectric]

@Atmasphere
We’ve had this same discussion before. Your comments about voltage drop miss the point. In a previous exchange on WBF, perhaps this thread, I cited two examples which demonstrate that rectifiers can sound different irrespective of voltage drop.

First, one of my linestages has a solid state regulator that keeps the B+ at 275v. The incoming voltage is typically 400v but it varies depending on which rectifier tube is used. I have tried 5u4G, 5ar4 and 5r4gy. They all sound different despite the regulated B+ remaining constant at 275v.

Second, in all my preamps and amps, I have tried different brands of the same type of rectifier tube. On my amps I use 5u4gb and I have tried RCA, GE, Sylvania, Raytheon, Tung Sol and Ken-Rad; they all sound different even after extended use, despite having the same voltage drop. On my preamps I use 5r4gy mostly and I have tried several brands and they all sound different. Again, same tube specs, same voltage drop, yet different sound.

I am not going to lose sleep wondering WHY rectifier tubes sound different. From my own experience I know they do, so rectifiers are just one more tool in my toolbox for tweaking the sound to get what I want.

Frankly I would be surprised if rectifier tubes did NOT affect sound quality. Consider some other things in the power supply that do affect sound quality (again, in my experience)—-IEC inlets, chokes, capacitors, connecting wires. Why would the rectifier be different? As important a function as it provides, why should it be somehow immune from impacting sound quality?

I fully realize written explanations or descriptions are not going to persuade you, so why not try a simple experiment. Just wire in a simple solid state series regulator in the B+ of a tube preamp. Allow enough headroom for a variety of incoming voltages. Then try different rectifier types or even different brands of the same rectifier type. Do you hear a difference?

 

[SVS]

I have 1960s winged “C” NOS tubes. They are branded 5?3C and are military (stamped OTK).

Only stamped OTK is a civilian destination. In addition to OTK, the recruitment designation has a rhombus with a number inside.

 

[SVS]

If there is an assumption that with higher Voltage the amp will sound better, then its time to dash it; obviously that is incorrect. The amp will sound its best when the circuit is operating at the best operating points. The big influence is likely the operating point of the power tube, since most DHTs have a very low mu (and are thus more susceptible to B+ variation than higher mu tubes as might be found in the driver/Voltage amplifier section). A 40V difference is going to put the power tube off its operating point and distortion will rise. You stand a good chance, depending on the tube, of also cooking it.

Its the same as if you underbias or over-bias the tube- once you are off the ideal point, on either side distortion rises. You can hear this distortion as coloration and loss of detail since distortion obscures detail and distortion is interpreted by the ear as tonality. Its audible.

I don't know why this should be mysterious; guitar players have been tinkering with this phenomena for years now, since its possible to easily vary the power supply voltage with modern semiconductors, to mimic failing capacitors and weak rectifiers, with a twist of a knob for that 'blues sound'.

Very few amplifiers, exclusively of original manufacture, are designed to work with used tubes. Even more strange is the situation when the amplifier is designed to work better with used tubes than with new ones. Maybe your amps are designed that way?

 

[Atmasphere]

@Atmasphere
We’ve had this same discussion before. Your comments about voltage drop miss the point. In a previous exchange on WBF, perhaps this thread, I cited two examples which demonstrate that rectifiers can sound different irrespective of voltage drop.

First, one of my linestages has a solid state regulator that keeps the B+ at 275v. The incoming voltage is typically 400v but it varies depending on which rectifier tube is used. I have tried 5u4G, 5ar4 and 5r4gy. They all sound different despite the regulated B+ remaining constant at 275v.

Second, in all my preamps and amps, I have tried different brands of the same type of rectifier tube. On my amps I use 5u4gb and I have tried RCA, GE, Sylvania, Raytheon, Tung Sol and Ken-Rad; they all sound different even after extended use, despite having the same voltage drop. On my preamps I use 5r4gy mostly and I have tried several brands and they all sound different. Again, same tube specs, same voltage drop, yet different sound.

I am not going to lose sleep wondering WHY rectifier tubes sound different. From my own experience I know they do, so rectifiers are just one more tool in my toolbox for tweaking the sound to get what I want.

Frankly I would be surprised if rectifier tubes did NOT affect sound quality. Consider some other things in the power supply that do affect sound quality (again, in my experience)—-IEC inlets, chokes, capacitors, connecting wires. Why would the rectifier be different? As important a function as it provides, why should it be somehow immune from impacting sound quality?

I fully realize written explanations or descriptions are not going to persuade you, so why not try a simple experiment. Just wire in a simple solid state series regulator in the B+ of a tube preamp. Allow enough headroom for a variety of incoming voltages. Then try different rectifier types or even different brands of the same rectifier type. Do you hear a difference?

We found that changing to HEXFRED rectifiers had a pretty noticeable improvement in the sound of our amps! That was 30 years ago. The reason why is simply that HEXFREDs are some of the fastest solid state rectifiers with the softest recovery. They are very easy to snub.

I don't doubt your word here- and you are being pragmatic in accepting the changes the rectifiers bring. But if they do so, there is a reason why and its very likely measurable. I suspect if not actual B+ voltage, it might be due to the capacitance of the rectifier interacting with the power transformer's inductance- this causes a high frequency resonance which can oscillate, known as a 'swept resonance'. Imagine RFI riding on the B+ that is pulsing at the line frequency. If you have a good oscilloscope you can see this sort of thing. Usually it can result in a slight buzz at the output of the amplifier (at least it can in our amps) because the RFI gets rectified due to non-linearities in the amplifier circuit.

Now I've yet to see anyone snubbing tube rectifiers like you have to do with solid state, but it strikes me that the only reason is the noise they make is lower than that of semiconductors. I've also noticed that a lot of SET users acquiesce to a certain amount of amplifier noise floor on high efficiency speakers that they say is near impossible to tune out due to the nature of DHTs. Perhaps they are barking up the wrong tree?

This swept resonance had a pretty big effect on the sound in our amps. If its not B+ voltage, could the differences in how tube rectifiers interact be what is going on? This would be easy to test by putting the amp on the bench and looking at the noise floor. When the rectifier is properly snubbed, you can see the noise floor improve. IME this has a direct effect on a kind of distortion known as 'inharmonic distortion' which is a kind of IMD. Rather than an interaction between fundamental tones, its caused by the signal interacting with a set tone inherent in the amplifier. This is one reason why getting a good noise floor is important. Aliasing of digital audio is a form of inharmonic distortion. Its pretty audible. I think this is worth looking into.

Very few amplifiers, exclusively of original manufacture, are designed to work with used tubes. Even more strange is the situation when the amplifier is designed to work better with used tubes than with new ones. Maybe your amps are designed that way?

I think you may have misread my post.

 

[Maril555]

OT

Only stamped OTK is a civilian destination. In addition to OTK, the recruitment designation has a rhombus with a number inside.

"OTK" means "quality control"

 

[SVS]

OTK" means "quality control"

literally OTK means "department of technical control" (????? ???????????? ????????).
They check finished products and allow their delivery to consumers in the case of civilian use. In the case of a military assignment, the OTK hands over the products accepted by them to military control. Further, the military is responsible for the quality of the product.

 

[SVS]

I think you may have misread my post.

Maybe you wanted to talk about elementary things.
"If there is an assumption that with higher Voltage the amp will sound better, then its time to dash it; obviously that is incorrect."
In general, this is correct, but in this particular case it turned out awkwardly.

 

[Blue58]

“Now I've yet to see anyone snubbing tube rectifiers like you have to do with solid state, but it strikes me that the only reason is the noise they make is lower than that of semiconductors. ‘

I always snub mine according to the work done by John Swenson. Cap + resistor across secondary.

‘I've also noticed that a lot of SET users acquiesce to a certain amount of amplifier noise floor on high efficiency speakers that they say is near impossible to tune out due to the nature of DHTs.”

True, I just live with it.

 

[SVS]

‘I've also noticed that a lot of SET users acquiesce to a certain amount of amplifier noise floor on high efficiency speakers that they say is near impossible to tune out due to the nature of DHTs.”

True, I just live with it.

You can hear noise in the speakers, such as crackling and gurgling, these are the thermal noises of the tubes and you cannot get rid of them. But this noise is very small, even in sensitive speakers.
But there is also hum, noise with the frequency of alternating current or double the frequency of alternating current. This hum should not be present at all in a good amplifier.

 

[Blue58]

You can hear noise in the speakers, such as crackling and gurgling, these are the thermal noises of the tubes and you cannot get rid of them. But this noise is very small, even in sensitive speakers.
But there is also hum, noise with the frequency of alternating current or double the frequency of alternating current. This hum should not be present at all in a good amplifier.

Hum I’m afraid but not noticeable from listening position (100Hz -86dB). The Duos are 107dB and I’m using small chokes in the power supply (blame Dennis and Jeff).

Maybe not a good amplifier but it sounds stunning to me.

cheers
Blue58

 

[crosswind]

Both chokes in place. Leif told med to give them 50 hours before serious listening. In the meantime the Hørning OPTs are getting prepared.

 

[bonzo75]

Both chokes in place. Leif told med to give them 50 hours before serious listening. In the meantime the Hørning OPTs are getting prepared.

View attachment 114858View attachment 114859

Try the Devores with a straight on position. How far are they from that front wall

 

[LL21]

Looks like about 2-2.5 feet? 60-75cm? I recall you like a lot of space for the Devores...1-1.2m'ish?

 

[LL21]

BTW, that closeup image is a well taken shot. Was that a phone or a camera?

 

[crosswind]

Try the Devores with a straight on position. How far are they from that front wall

Will do. They are 110 cm from the front wall and the left speaker 120 cm from the left wall. (All measured from center/front of drivers) I am planning of moving them 50 cm away from the left wall but I am unable to move them much more out from the front wall because of the listening position being stuck. The sofa can’t move further aft as you can se in the pic.

 

[crosswind]

BTW, that closeup image is a well taken shot. Was that a phone or a camera?

Thank You. iPhone 13.

 

[bonzo75]

Will do. They are 110 cm from the front wall and the left speaker 120 cm from the left wall. (All measured from center/front of drivers) I am planning of moving them 50 cm away from the left wall but I am unable to move them much more out from the front wall because of the listening position being stuck. The sofa can’t move further aft as you can se in the pic.

View attachment 114860

ok. if you straighten them you can get them slightly in towards each other as compared to when toed in.