Tube amp question or opinions

[HTEnthusiast]

I always want a tube somewhere in the path, but I’m not a fan of full tube amplifiers. I guess if you get to the uber expensive/powerful ones, you may be ok, but the lesser ones just don’t control the speaker like solid state amplifiers.

I think a tube in the path brings back a “naturalness“, that is lost in the recording. I personally have had tube preamps in my stereo systems and solid state amps. Because there are no tube home theater processors, I have a tube phono preamp In my theater. I had a Musical Paradise tube DAC, but didn’t really like it.

The best solution I’m looking for is a hybrid amp with a tube input stage and solid state power. This is the way Paul McGowan designed his PS Audio reference amps.

 

[TLS Guy]

I always want a tube somewhere in the path, but I’m not a fan of full tube amplifiers. I guess if you get to the uber expensive/powerful ones, you may be ok, but the lesser ones just don’t control the speaker like solid state amplifiers.

I think a tube in the path brings back a “naturalness“, that is lost in the recording. I personally have had tube preamps in my stereo systems and solid state amps. Because there are no tube home theater processors, I have a tube phono preamp In my theater. I had a Musical Paradise tube DAC, but didn’t really like it.

The best solution I’m looking for is a hybrid amp with a tube input stage and solid state power. This is the way Paul McGowan designed his PS Audio reference amps.

You won't get much traction here, as we don't believe in magic. You have so show by measurements that the tube is better than an IC or transistor and you can't. If you split hairs it is worse.

You have been deluded by Audiophool BS. They look nice and pretty in some rigs, but an audible benefit NO!

I do have one tube preamp in my rig, but that is because it has the Eq for all the old 78 recordings from the various companies. They all had different curves. Does it sound better or even different from the solid state preamps on the other turntables? No.

 

[HTEnthusiast]

There's these two, anyone wanting or needs a fix for Nostalgia, feeling of days gone by of gear with VU meter's. .ASR, site tested and gave his recommendation.
View attachment 65439
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Gone are the days of following the Buffalo across the prairie.

I went through a short phase of chasing equipment based on measurements. I had a Benchmark DAC and Placette Remote Volume Control, providing an almost unmeasurably transparent path. I also bought a couple DACs recommended by ASR, but returned them.

In every case, I ended up with incredibly detailed, but (from my perspective) boring sound. I really appreciate what ASR is doing, but I use their reviews as one aspect of input verses ignoring stuff that happens to not be totally transparent from a measurement perspective.

 

[highfigh]

That Dynaco is not original. The PC board is new and different. A tube has been added which must be a dual tube shared between channels. This is probably not a good idea and likely to lead to some crosstalk.

A lot of these units have been modified. Only about 5% of these units are factory. 95% were bought as kits and built by the original owners.

I haven't seen many ST-70 in the wild, but the third tube seemed odd and as I suspected, the modification changes the two 7199 to 12Ax7 and adds the third tube as the phase inverter.

 

[highfigh]

My old stuff has been restored and works fine and I still use it occasionally. I have an Adcom GFA-5500 and and my first Pioneer amp which is an SA-8500 among others. But I won't be rebuilding them again or adding to the collection. If they had bass management, I'd still be using them full time.

But still, it's just so much easier and more efficient with class D stuff, or even the A/B stuff from the last couple decades and without those dreadful analog pots. It's been all about the speakers (provided the amps are capable) for me for the last 30 years or so anyway.

I have some other MOSFET amps from 8-25 watts that I amuse myself with occasionally, but this class D stuff is getting too good to ignore.

I bought the Kenwood KR3130 about 30 years ago (I think it cost $50) because I wanted a receiver for my basement that had pre out/power amp in and it has been through three incidents where I had water coming in from storms. It wasn't deep, but it really jacked up the humidity- no problems, ever. The Sony STR-5800SD has been in my original garage and the current one, which means I have owned it since before 2003. I saw it near the alley at the house next door to my parents and it was night, so I grabbed it. When I saw their neighbor, I asked if it was fair game and he said yes. I liked that series when they were current models at the stereo store where I worked, so I plugged it in- lights on, nobody home. I took it to the service tech at the stereo store and he replaced a bad regulator- I bought his lunch, but he didn't bother to repair the tuning indicator which is one thin red LED that's lit when the tuner is used and the second LED illuminates when the tuner locks onto the station.

 

[TLS Guy]

I haven't seen many ST-70 in the wild, but the third tube seemed odd and as I suspected, the modification changes the two 7199 to 12Ax7 and adds the third tube as the phase inverter.

I suspect you are right, but it has to be a double tube, and raises the issue of channel crosstalk. I suspect it was added by an absolute phase nutter. They don't realize you can do it simpler and cheaper by reversing the speaker terminals! A lot of older amps are phase inverting. For instance the Quad 405s are phase inverting and the 909s are not. So in my system the 405-IIs powering the ceiling Atmos speakers have the speaker cables reversed. Simple. You don't need active electronics to do that.

 

[TLS Guy]

I went through a short phase of chasing equipment based on measurements. I had a Benchmark DAC and Placette Remote Volume Control, providing an almost unmeasurably transparent path. I also bought a couple DACs recommended by ASR, but returned them.

In every case, I ended up with incredibly detailed, but (from my perspective) boring sound. I really appreciate what ASR is doing, but I use their reviews as one aspect of input verses ignoring stuff that happens to not be totally transparent from a measurement perspective.

So you put your faith in some self important know nothing guru in the audiophool mags?

 

[highfigh]

I suspect you are right, but it has to be a double tube, and raises the issue of channel crosstalk. I suspect it was added by an absolute phase nutter. They don't realize you can do it simpler and cheaper by reversing the speaker terminals! A lot of older amps are phase inverting. For instance the Quad 405s are phase inverting and the 909s are not. So in my system the 405-IIs powering the ceiling Atmos speakers have the speaker cables reversed. Simple. You don't need active electronics to do that.

Those tubes do have two halves- If it's complementary Push-pull, which it is, it needs a PI. I didn't see the number of the PI in this one, but the GE 12AU7 replace the original 7199 tubes and the photo didn't show the PI (and I'm not going to search for it) but other amps, like the Conrad Johnson MV45 that I had used 12AT78 for the PI. My '58 Fender Bassman amp originally uses a 12AX7 for the PI although the 12AT, 12AU, 12AY could be used- it's not a high current application and some people like to reduce the headroom.

The ST-70 is from 1959, when tubes were the output devices used by just about everyone- in order to make an amplifier that wouldn't cost too much, 6L6 or El34 were used in these Push-pull configurations because that's the only way they could reach the output power they wanted. 6V6 or EL84 surely wouldn't be enough power, so these were used.

Why are you comparing the 35 W/channel ST-70 to a 140W/channel solid state amplifier that became available in 1999?

 

[TLS Guy]

Those tubes do have two halves- If it's push-pull, which it is, it needs a PI. I didn't see the number of the PI in this one, but the GE 12AU7 replace the original 7199, but other amps, like the Conrad Johnson MV45 that I had used 12AT78 for the PI. My '58 Fender Bassman amp originally uses a 12AX7 for the PI although the 12AT, 12AU, 12AY could be used- it's not a high current application and some people like to reduce the headroom.

The ST-70 is from 1959, when tubes were the output devices used by just about everyone- in order to make an amplifier that wouldn't cost too much, 6L6 or El34 were used in Push-pull configurations because that's the only way they could reach the output power they wanted. 6V6 or EL84 surely wouldn't be enough power, so these were used.

Why are you comparing the 35 W/channel ST-70 to a 140W/channel solid state amplifier that became available in 1999?

I'm not comparing it. I was just making the point that you don't have to add a tube to invert phase if you believe the audiophool nonsense about absolute phase. If you have a phase inverting amp you just need to reverse the speaker wires. This is only an issue to worry about, if you have non phase inverting and phase inverting amps, in the same system, as I do. Then you need to reverse the speaker connections to the phase inverting amps.

 

[highfigh]

I'm not comparing it. I was just making the point that you don't have to add a tube to invert phase if you believe the audiophool nonsense about absolute phase. If you have a phase inverting amp you just need to reverse the speaker wires. This is only an issue to worry about, if you have non phase inverting and phase inverting amps, in the same system, as I do. Then you need to reverse the speaker connections to the phase inverting amps.

When the power outputs can be fed by far less voltage from the power supply and develop more gain, of course no PI is needed.

 

[TLS Guy]

When the power outputs can be fed by far less voltage from the power supply and develop more gain, of course no PI is needed.

I'm sorry but I don't understand your issue. Phase inversion has absolutely no relationship to amp power or gain. It is purely related to the topography of the phase splitter stage and the push pull output stage. So high and low power amps can be phase inverting or not.

 

[lovinthehd]

I went through a short phase of chasing equipment based on measurements. I had a Benchmark DAC and Placette Remote Volume Control, providing an almost unmeasurably transparent path. I also bought a couple DACs recommended by ASR, but returned them.

In every case, I ended up with incredibly detailed, but (from my perspective) boring sound. I really appreciate what ASR is doing, but I use their reviews as one aspect of input verses ignoring stuff that happens to not be totally transparent from a measurement perspective.

Why not just use a tubey plugin or eq ? Clean electronics do not make audio boring....that's your brain most likely.

 

[highfigh]

I'm sorry but I don't understand your issue. Phase inversion has absolutely no relationship to amp power or gain. It is purely related to the topography of the phase splitter stage and the push pull output stage. So high and low power amps can be phase inverting or not.

The inverter isn't used in Single Ended amplifiers, right? The inverted phase creates a voltage differential between the phases going to the output transformer and then, to the speaker(s)- are you thinking in terms of inverted stereo channels or the signal in a Push-Pull channel?

 

[TLS Guy]

The inverter isn't used in Single Ended amplifiers, right? The inverted phase creates a voltage differential between the phases going to the output transformer and then, to the speaker(s)- are you thinking in terms of inverted stereo channels or the signal in a Push-Pull channel?

You are still a little confused, but getting there.

In the single ended amplifier there is no phase shift between input and output generally.

In the push pull tube and solid state push pull era, the speaker output was generally 180 degrees out of phase with the input. This was of no consequence, and no one cared until the Audiophool era. Then the concept of absolute phase became a mantra of the audiophilia crowd. This was particularly popularized by Sam Tellig a real nut job guru on Stereophile. He was eloquent about the issue of if a trumpet say, had a positive wave at a given moment, but the speaker wave was negative, that it was a massive audio transgression. So the bogus concept of absolute phase was popularized. So any amp with the speaker output 180 degrees out of phase with the input was declared junk, notwithstanding the fact that if you connected your speakers +ve to -ve at the amp speaker terminals you solved the problem. At that time almost all power amps had the speakers 180 degrees out of phase with the input.

Now in the days of stereo this was of no consequence. This changed in the HT era and multiple speakers, if people were mixing power amps. They were confused about Audyssey etc, reported out of phase conditions, when the users thought they had their amps connected to their speakers correctly. Whether an amp was phase inverting or not was not generally included on the spec, so a consumer was not aware that the first deflection of the positive speaker terminal was negative and not positive.

So if a user like myself who uses an amp combination, you need to be aware of the phase relationship between amp input and output. We probably don't mention this enough.

My case is classic. The Quad 909s were introduced in 1999 in the 'absolute pase' era. The 405 series in 1973 before this nonsense started of phase inverting between input and output.

So my speakers connected to the 909s are connected positive to positive, but my ceiling speakers connected to the 405-II amps are connected positive to negative. That is correct and Audyssey is happy.

These are the phase angles if you connected two signals of varying phase to the X and Y plates of an O-Scope.

I hope this clears it up for you.

 

[highfigh]

You are still a little confused, but getting there.

In the single ended amplifier there is no phase shift between input and output generally.

In the push pull tube and solid state push pull era, the speaker output was generally 180 degrees out of phase with the input. This was of no consequence, and no one cared until the Audiophool era. Then the concept of absolute phase became a mantra of the audiophilia crowd. This was particularly popularized by Sam Tellig a real nut job guru on Stereophile. He was eloquent about the issue of if a trumpet say, had a positive wave at a given moment, but the speaker wave was negative, that it was a massive audio transgression. So the bogus concept of absolute phase was popularized. So any amp with the speaker output 180 degrees out of phase with the input was declared junk, notwithstanding the fact that if you connected your speakers +ve to -ve at the amp speaker terminals you solved the problem. At that time almost all power amps had the speakers 180 degrees out of phase with the input.

Now in the days of stereo this was of no consequence. This changed in the HT era and multiple speakers, if people were mixing power amps. They were confused about Audyssey etc, reported out of phase conditions, when the users thought they had their amps connected to their speakers correctly. Whether an amp was phase inverting or not was not generally included on the spec, so a consumer was not aware that the first deflection of the positive speaker terminal was negative and not positive.

So if a user like myself who uses an amp combination, you need to be aware of the phase relationship between amp input and output. We probably don't mention this enough.

My case is classic. The Quad 909s were introduced in 1999 in the 'absolute pase' era. The 405 series in 1973 before this nonsense started of phase inverting between input and output.

So my speakers connected to the 909s are connected positive to positive, but my ceiling speakers connected to the 405-II amps are connected positive to negative. That is correct and Audyssey is happy.

These are the phase angles if you connected two signals of varying phase to the X and Y plates of an O-Scope.

I hope this clears it up for you.

The only thing that's clear is that we're not referring to phase shift as the same concept. You're looking at the relative phase WRT in/out, I'm referring to the two halves of the sine wave at the output, where they're mixed after leaving the PI where one half remains as it entered and the other is inverted, to create a larger voltage differential. The Dynaco, which is the item in the OP's topic, uses a PI for the complementary P-P output, not for absolute or relative phase.

The link is for a guitar/bass amp and it's similar enough for the purpose of the concept I'm referring to. And BTW- that amp's output is the inverse of the input but by being only one channel, it's not important. If it were a stereo amp, it would be important and reversing the speaker wires would be needed if they hadn't dealt with it internally.

Fender Bassman 5F6-A Circuit Analysis

www.ampbooks.com

 

[TLS Guy]

The only thing that's clear is that we're not referring to phase shift as the same concept. You're looking at the relative phase WRT in/out, I'm referring to the two halves of the sine wave at the output, where they're mixed after leaving the PI where one half remains as it entered and the other is inverted, to create a larger voltage differential. The Dynaco, which is the item in the OP's topic, uses a PI for the complementary P-P output, not for absolute or relative phase.

The link is for a guitar/bass amp and it's similar enough for the purpose of the concept I'm referring to. And BTW- that amp's output is the inverse of the input but by being only one channel, it's not important. If it were a stereo amp, it would be important and reversing the speaker wires would be needed if they hadn't dealt with it internally.

Fender Bassman 5F6-A Circuit Analysis

www.ampbooks.com

Well, I think we agree. The original Dynaco ST70 did have the input and output 180 degrees out of phase. I know that certain as I owned one. This was the usual arrangement and only became an issue because of Audiophools banging on about absolute phase. Which if you think about it is absolute nonsense as is typical of those idiots. Anyhow it led to power amps being set up so that the first deflection of a wave was up and positive, as it would be negative on the original ST 70s. So I think that added tube in the amp at the start of this thread was added to reverse the situation so the +ve terminal has an upward deflection.

So it now means that you have to know whether the output is in or out of phase with the input when mixing amps in an HT system. That really is all there is to it.

 

[highfigh]

Well, I think we agree. The original Dynaco ST70 did have the input and output 180 degrees out of phase. I know that certain as I owned one. This was the usual arrangement and only became an issue because of Audiophools banging on about absolute phase. Which if you think about it is absolute nonsense as is typical of those idiots. Anyhow it led to power amps being set up so that the first deflection of a wave was up and positive, as it would be negative on the original ST 70s. So I think that added tube in the amp at the start of this thread was added to reverse the situation so the +ve terminal has an upward deflection.

So it now means that you have to know whether the output is in or out of phase with the input when mixing amps in an HT system. That really is all there is to it.

I don't care about the input and output being reversed! The PI is used for inverting half of the signal in order to increase the output voltage.

 

[TLS Guy]

I don't care about the input and output being reversed! The PI is used for inverting half of the signal in order to increase the output voltage.

Well we are both wrong.

After doing some investigation the extra tube was just to separate the voltage amplification from the phase splitter.

This is the circuit for the VTA board modification which is the board with the three tubes.

So the board has three 12AT7 tubes. The two halves of one provide voltage amplification for each chanel, then the other two tubes provide the complementary phase splitting as the drivers for the EL84 output tubes.

This is the original circuit.

Voltage amplification is from one half of the 7199 tube. The other half of each tube is the phase splitter to drive the output tubes.

Of course claims were made of improved performance, but I suspect the reason is the 7199s are hard to source, and 12AT7s are plentiful. This mod did provide performance below 20 Hz for what that is worth. Both circuits would have the output 180 degrees out of phase with the input. The output stage with complimentary EL-34s is the same in both versions.

 

[highfigh]

Well we are both wrong.

After doing some investigation the extra tube was just to separate the voltage amplification from the phase splitter.

This is the circuit for the VTA board modification which is the board with the three tubes.

So the board has three 12AT7 tubes. The two halves of one provide voltage amplification for each chanel, then the other two tubes provide the complementary phase splitting as the drivers for the EL84 output tubes.

This is the original circuit.

Voltage amplification is from one half of the 7199 tube. The other half of each tube is the phase splitter to drive the output tubes.

Of course claims were made of improved performance, but I suspect the reason is the 7199s are hard to source, and 12AT7s are plentiful. This mod did provide performance below 20 Hz for what that is worth. Both circuits would have the output 180 degrees out of phase with the input. The output stage with complimentary EL-34s is the same in both versions.

Ugh- that's what I get for thinking it was similar to the Conrad-Johnson amp I mentioned.........

Did this help in the higher frequencies as well as <20Hz?

 

[TLS Guy]

Ugh- that's what I get for thinking it was similar to the Conrad-Johnson amp I mentioned.........

Did this help in the higher frequencies as well as <20Hz?

I don't think so, as the limit to that would be the output transformer, but the Dynaco easily makes 20K. As usual there was a lot of folderal about this. I would bet the real reason was actually sourcing the tubes.