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  • #31
    Originally posted by Chuck H View Post
    The PI starts to clip just after the power tubes.

    Thats it...Enjoy

    Chuck
    Good solution; this avoids driving the power tube grids hard enough to provoke a bias shift.

    Comment


    • #32
      Originally posted by Chuck H View Post
      Ok. Just for giggles I looked at a bunch of Traynor schems. Two of them were for the yba1a mkII with over 500 volts on the plates ('69 and '70). Both of them had the supressor tied to 0V rail (ground). But this is not to say that a later model didn't use the supressor grid differently. I had a later model Bassmaster that did have the supressors wired the way you describe. For what it's worth it was a great amp. I still have it though it's circuitry no longer resembles the schematic in any way. This amp was a mod test platform for many years. But don't worry. It's not a real collectible. It's one of the later models with the over/under channel inputs seperated by the controls.

      Anyway, I also looked up a Musicman 150 schem. These are widely regarded as the most efficient tube instrument amps. They run the power tube grids from what appears to be a source follower (provides the grids with a limited current path) and run the plates of four 6L6 tubes at 700 volts. By the schem I would say these are AB2 amps. Each 6L6 is good for 37.5 watts in this amp. Musicman also made a "75" with two tubes. Let me state for the record that you would not want to overdrive one of these amps. Aside from hearing loss there would be substantial crossover distortion. These were not designed to be pushed into overdrive conditions. They ran substantially more plate voltage and a different class of operation than the yba1a and still only got a meager 75 watts from a pair of big bottles.

      Now I'm going to say what I really think. Not because I'm mean. It's because I'm an obsessive truth pounding a$$ho!e that most people eventually learn to dislike.

      Your repeated use of the "sine" indication and the wattages of 25 for the guitarmate and 90 for the Bassmaster are spot on with the vintage literature on the Yorkville website. I believe that you have no direct knowledge of the actual output of these amps and are instead just reprinting what you've read from what you believe to be a responsible source of information. It's not. Stop doing it. Or you could answer my first question on this subject. How did you measure the output of these amps? Please include details.

      Chuck

      Sure, but first let me say that I am I bit offended by your comment and assumption that I am a liar and have never actually measured the output of these amps. I have been an amp tech for many years now and do know how to measure power output from an amplifier. I do it the same way most people do into a resistive load while monitoring the output on a scope just before clipping and measuring the the true RMS AC voltage on my Fluke 87. I then use ohms law to calculate the power. The only reason I said unclipped sine wave was to insure you that I wasn't using a clipped waveform to calculate the power.

      Comment


      • #33
        Originally posted by voxrules! View Post
        Hi again ETR,

        The primary ( or each half of it ) is a current ring, the current flows from the +B to GND through the tube(s), this means whatever current flows from the PT in the OT has to flow in the tube(s), they can never be treated independently....if the PT and the OT can handle a lot of current, this doesn't mean the tubes can do the same.

        As to the schematic, I've seen other Guitarmate schematics with 7189s, though I don't have the link at hand...

        You're stating you measured many times 25 W unclipped, so, at this point, as Chuck already asked, I would like to ask you about the method you used for your measurements.

        Best regards

        Bob
        I am not treating them indepedently. What most people miss about power supplies in tube amps is the sag due to the current flow that occurs when the amp is cranking. Just because at some bias point the static idle plate voltage is somewhere tells you relatively nothing about the whole picture. So what I say to you is don't treat the voltage independently from the current.

        Comment


        • #34
          Originally posted by Chuck H View Post
          Ok. Just for giggles I looked at a bunch of Traynor schems. Two of them were for the yba1a mkII with over 500 volts on the plates ('69 and '70). Both of them had the supressor tied to 0V rail (ground). But this is not to say that a later model didn't use the supressor grid differently. I had a later model Bassmaster that did have the supressors wired the way you describe. For what it's worth it was a great amp. I still have it though it's circuitry no longer resembles the schematic in any way. This amp was a mod test platform for many years. But don't worry. It's not a real collectible. It's one of the later models with the over/under channel inputs seperated by the controls.

          Anyway, I also looked up a Musicman 150 schem. These are widely regarded as the most efficient tube instrument amps. They run the power tube grids from what appears to be a source follower (provides the grids with a limited current path) and run the plates of four 6L6 tubes at 700 volts. By the schem I would say these are AB2 amps. Each 6L6 is good for 37.5 watts in this amp. Musicman also made a "75" with two tubes. Let me state for the record that you would not want to overdrive one of these amps. Aside from hearing loss there would be substantial crossover distortion. These were not designed to be pushed into overdrive conditions. They ran substantially more plate voltage and a different class of operation than the yba1a and still only got a meager 75 watts from a pair of big bottles.

          Now I'm going to say what I really think. Not because I'm mean. It's because I'm an obsessive truth pounding a$$ho!e that most people eventually learn to dislike.

          Your repeated use of the "sine" indication and the wattages of 25 for the guitarmate and 90 for the Bassmaster are spot on with the vintage literature on the Yorkville website. I believe that you have no direct knowledge of the actual output of these amps and are instead just reprinting what you've read from what you believe to be a responsible source of information. It's not. Stop doing it. Or you could answer my first question on this subject. How did you measure the output of these amps? Please include details.

          Chuck
          If it helps illustrate the point I'm making lets forget about Traynors. Bogner Shivas put out a true 80 watts RMS unclipped sinewave with 2 6L6's and yes I have measured many of them. Groove tubes Solo 75's can do 75 watts unclipped with the same power tubes and about 90 with 6550's and yes I have measured them many times as well. I have even measured better than 70 watts out of a vintage Univox 100 watt amp that was using a pair of 6L6's. If it gives you something to gauge my measurements I have rarely seen better than 72 watts out of a "85 watt" BF Fender or better than 36 watts out of a "50 watt" Bassman.

          Comment


          • #35
            Ok. White flag. I have not measured the output on nearly the number of amps you claim. Perhaps these designers know some magic trick we don't. But on the macro view it surely looks impossible.

            I apologize for comming foreward with my suspicions. What you may suspect of anyone before you have the facts is best kept to ourselves. It was slanderous and wrong. Even if the facts "I" have demonstrate that your full of bologna, it doesn't mean your facts are wrong. At the very least you clearly believe they are right. There are plenty of facts that contradict.

            I am sorry. And possibly even wrong on this. Even though I don't think so, I am willing to admit this much.

            Chuck
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "If you're not interested in opinions and the experience of others, why even start a thread?
            You can't just expect consent." Helmholtz

            Comment


            • #36
              Originally posted by ETR View Post
              I am not treating them indepedently. What most people miss about power supplies in tube amps is the sag due to the current flow that occurs when the amp is cranking. Just because at some bias point the static idle plate voltage is somewhere tells you relatively nothing about the whole picture. So what I say to you is don't treat the voltage independently from the current.
              Hi again ETR,
              If we're talking about the guitarmate YGM-1, whatever sag would come from the cathode bias arrangement, not from the power supply/rectifier, as the rectifier is a solid-state one, and its inherent differential resistance is way lower than the one a tube rectifier has....this is proved by the fact many people puts Weber "copper caps" in their amps to simulate the tube rectifier sag while keeping/getting the benefits of a solid state rectifier. As I already discussed in another thread, a homebrew solution to achieve this is to add series resistors to a solid state rectifier to get some "sag" out of it.

              This leads us to another point:

              If you want to "squeeze" the most ( in terms of power and headroom ) from an AB1 push-pull design, you need to use a fixed ( external ) bias source, because the "cathode bias" ( which I find superior tone-wise ) design is a self-regulating one to some degree: as the current through the cathode resistor increases following the signal's amplitude, so does the voltage drop across it, thus less voltage drops across the tube's plate and cathode, so it's just like the tube is being supplied with a lower B+. This results in some sag, less headroom ( and output power ). I think this is the reason why Traynor switched from cathode ( YGM-1 ) to fixed ( YGM-2-3-4 ) bias, but I still think ( together with other people way more experienced than I am ) that it's not possible to achieve 25 W RMS out of a pair of EL84 while operating them within their safe limits.

              I will change my mind only when I will have a positive proof that contradicts my belief. If you, as you stated, are measuring the output power on a purely resistive load ( dummy ) then you' re not running your test under "real world" conditions, a dummy load is not a speaker, as a dummy load does not change its impedance, thus offering a perfect match at all frequencies, it has only a resistive behavior with no losses, all the power is converted to heat ( not sound ) while a speaker does have some losses, both in the wire and in the coil spacing, has some inductance too, and its impedance changes along with frequency, so it does not offer a perfect match at all frequencies; besides, some of the power gets wasted along the way due to the coil resistance ( Joule effect, thus it's not useful power, as it only heats the coil and the magnet without producing sound ). Try using a real speaker instead of a dummy load for your measurements and see for yourself....I think your amp will start to clip much earlier and at a lower power.
              Best regards

              Bob
              Last edited by Robert M. Martinelli; 01-06-2009, 03:47 PM.
              Hoc unum scio: me nihil scire.

              Comment


              • #37
                Originally posted by voxrules! View Post
                ...Try using a real speaker instead of a dummy load for your measurements and see for yourself....I think your amp will start to clip much earlier and at a lower power.
                Best regards

                Bob
                If that was true, it would only be so if he can figure out how to measure the true impedance of the speaker at those frequencies which he is testing for power output. Most guys testing with a speaker make this error and end up using the wrong impedance number in their math expression.
                As there are only a few places in the bandwidth where the speaker is the actual 4, 8 or 16 ohms, using those numbers to run your math at any frequencies close to the bandwidth ends of the speaker will net you a pretty significant error in power output.
                But, if you could get the true impedance, that would be the same as doing the math with a non reactive dummy load... so I think the dummy load is still the true way to measure output power, never with a highly reactive load such as a speaker.

                And by the way, I also don't think I've ever seen a pair of EL84s in a guitar amp make anymore then about 18-20 watts as measured with a clean input signal, clean PI drive signal and a pure sine wave coming out of the OT.... as overlapped with a perfectly clean input signal using a dual trace scope... and all that driving a dummy load.
                That doesn't mean there isn't an 2xEL84 amp out there that can hit a real clean 25 watts but usually it is less then 18 to 20 watts.

                Yes, I can see where it is possible with a very good output tranny and a stiff power supply with high DC voltage on the plates, you could get more power output with a subsequent loss of life in the tube.
                If class operation or longevity is not an issue at all it is possible to get an output from a power tube of around 160% of the tube's DC rating.
                Keep in mind, those XX watt power tube ratings are DC ratings, not AC power rating and I'm afraid most all the cheaper Russian EL84s aren't even as well made as NOS ones where these ratings came from.

                So, that means a really well made, single 12 watt EL84 could make about 19 watts of some kind of power (probably not linear in class A, but maybe in peak Class C) .... maybe two in PP Class AB2 "could" make clean peaks about 30 watts.... but not continuously.
                Regardless of what class you drive the tubes into, pushing that kind of an AC output through an EL84, unless water cooled or chimney mounted with a forced air chassis, isn't going to last more the a few nights or sets playing out.
                So with realistic costs, linear and longevity expectations in tow... I'll stick to the 18-20 watt limits.
                Bruce

                Mission Amps
                Denver, CO. 80022
                www.missionamps.com
                303-955-2412

                Comment


                • #38
                  Originally posted by voxrules! View Post
                  Hi again ETR,
                  If we're talking about the guitarmate YGM-1, whatever sag would come from the cathode bias arrangement, not from the power supply/rectifier, as the rectifier is a solid-state one, and its inherent differential resistance is way lower than the one a tube rectifier has....this is proved by the fact many people puts Weber "copper caps" in their amps to simulate the tube rectifier sag while keeping/getting the benefits of a solid state rectifier. As I already discussed in another thread, a homebrew solution to achieve this is to add series resistors to a solid state rectifier to get some "sag" out of it.

                  This leads us to another point:

                  If you want to "squeeze" the most ( in terms of power and headroom ) from an AB1 push-pull design, you need to use a fixed ( external ) bias source, because the "cathode bias" ( which I find superior tone-wise ) design is a self-regulating one to some degree: as the current through the cathode resistor increases following the signal's amplitude, so does the voltage drop across it, thus less voltage drops across the tube's plate and cathode, so it's just like the tube is being supplied with a lower B+. This results in some sag, less headroom ( and output power ). I think this is the reason why Traynor switched from cathode ( YGM-1 ) to fixed ( YGM-2-3-4 ) bias, but I still think ( together with other people way more experienced than I am ) that it's not possible to achieve 25 W RMS out of a pair of EL84 while operating them within their safe limits.

                  I will change my mind only when I will have a positive proof that contradicts my belief. If you, as you stated, are measuring the output power on a purely resistive load ( dummy ) then you' re not running your test under "real world" conditions, a dummy load is not a speaker, as a dummy load does not change its impedance, thus offering a perfect match at all frequencies, it has only a resistive behavior with no losses, all the power is converted to heat ( not sound ) while a speaker does have some losses, both in the wire and in the coil spacing, has some inductance too, and its impedance changes along with frequency, so it does not offer a perfect match at all frequencies; besides, some of the power gets wasted along the way due to the coil resistance ( Joule effect, thus it's not useful power, as it only heats the coil and the magnet without producing sound ). Try using a real speaker instead of a dummy load for your measurements and see for yourself....I think your amp will start to clip much earlier and at a lower power.
                  Best regards

                  Bob
                  I agree that the inductive properties of speakers change the power measurements but we need a way to compare apples to apples. That's why everybody that wants a true comparison uses a resistive load. Every speaker would read differently if you tried using that method and you would never know what you had. The amp I owned was a YGM3 and it's a fixed bias amp.

                  Sag mostly comes from the transformer in fixed bias amps. Actually that's where it mostly comes from in any amp. A tube rectifier can add to it and a cathode resistor if it's not in class A but most cathode bias amps are class A or close to it.

                  Comment


                  • #39
                    Originally posted by Chuck H View Post
                    Ok. White flag. I have not measured the output on nearly the number of amps you claim. Perhaps these designers know some magic trick we don't. But on the macro view it surely looks impossible.

                    I apologize for comming foreward with my suspicions. What you may suspect of anyone before you have the facts is best kept to ourselves. It was slanderous and wrong. Even if the facts "I" have demonstrate that your full of bologna, it doesn't mean your facts are wrong. At the very least you clearly believe they are right. There are plenty of facts that contradict.

                    I am sorry. And possibly even wrong on this. Even though I don't think so, I am willing to admit this much.

                    Chuck
                    Apology accepted. Just so you know I don't make false claims. I do think there are a lot of gray areas in tube guitar amps, much more so than hifi amps. Leo Fender pushed limits many times and his amps have stood the test of time. I do want to point out that if you run an amp at a much lower idle bias you are prone to more crossover distortion which is why most amps don't run so close to class B as the ones I have mentioned here. There is really no extra strain on the tubes when doing this since a watt is still a watt (remember average dissipation) but if you don't design in ways of dealing with the crossover distortion the amp could end up sounding bad, especially when clipping. Most of the amps I mentioned do have circuitry to deal with this. That's the real trick.

                    Comment


                    • #40
                      Originally posted by Bruce / Mission Amps View Post
                      If that was true, it would only be so if he can figure out how to measure the true impedance of the speaker at those frequencies which he is testing for power output. Most guys testing with a speaker make this error and end up using the wrong impedance number in their math expression.
                      As there are only a few places in the bandwidth where the speaker is the actual 4, 8 or 16 ohms, using those numbers to run your math at any frequencies close to the bandwidth ends of the speaker will net you a pretty significant error in power output.
                      But, if you could get the true impedance, that would be the same as doing the math with a non reactive dummy load... so I think the dummy load is still the true way to measure output power, never with a highly reactive load such as a speaker.

                      And by the way, I also don't think I've ever seen a pair of EL84s in a guitar amp make anymore then about 18-20 watts as measured with a clean input signal, clean PI drive signal and a pure sine wave coming out of the OT.... as overlapped with a perfectly clean input signal using a dual trace scope... and all that driving a dummy load.
                      That doesn't mean there isn't an 2xEL84 amp out there that can hit a real clean 25 watts but usually it is less then 18 to 20 watts.

                      Yes, I can see where it is possible with a very good output tranny and a stiff power supply with high DC voltage on the plates, you could get more power output with a subsequent loss of life in the tube.
                      If class operation or longevity is not an issue at all it is possible to get an output from a power tube of around 160% of the tube's DC rating.
                      Keep in mind, those XX watt power tube ratings are DC ratings, not AC power rating and I'm afraid most all the cheaper Russian EL84s aren't even as well made as NOS ones where these ratings came from.

                      So, that means a really well made, single 12 watt EL84 could make about 19 watts of some kind of power (probably not linear in class A, but maybe in peak Class C) .... maybe two in PP Class AB2 "could" make clean peaks about 30 watts.... but not continuously.
                      Regardless of what class you drive the tubes into, pushing that kind of an AC output through an EL84, unless water cooled or chimney mounted with a forced air chassis, isn't going to last more the a few nights or sets playing out.
                      So with realistic costs, linear and longevity expectations in tow... I'll stick to the 18-20 watt limits.

                      Heh heh he said stiff supply......

                      Comment


                      • #41
                        It's also possible that in an effort to get more power Traynor uppped the voltage even further on later year models for the YBA1A MKII. Get over 600 volts on the plates and tie the supressor to a -V rail and you could get higher than the "max" dissapation. Perhaps these are the ones that created any reality in the reputation. I still stretch at 90 watts but I've never had one on the bench.

                        Peace

                        Chuck
                        "Take two placebos, works twice as well." Enzo

                        "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                        "If you're not interested in opinions and the experience of others, why even start a thread?
                        You can't just expect consent." Helmholtz

                        Comment


                        • #42
                          Originally posted by Chuck H View Post
                          It's also possible that in an effort to get more power Traynor uppped the voltage even further on later year models for the YBA1A MKII. Get over 600 volts on the plates and tie the supressor to a -V rail and you could get higher than the "max" dissapation. Perhaps these are the ones that created any reality in the reputation. I still stretch at 90 watts but I've never had one on the bench.

                          Peace

                          Chuck
                          What you really need to get your head around is that it's not over max average dissipation if a 25 watt tube is doing 45 watts for only brief moments.

                          Comment


                          • #43
                            Well,

                            On one hand I'm happy Bruce confirmed my thoughts about output power, tubes' life and about current production tubes, and I'm also happy ETR agreed that things are indeed different with a speaker.

                            On the other hand I think I have been misunderstood about the "dummy load" vs. "speaker" point I raised. I use dummy loads myself, and have done so also in other fields ( building transmitters and testing TXs output stages before connecting them to real antennas ), I think they're great and, if you want to compare "apples with apples" ( thanks ETR ) they're just fine, so I was absolutely not questioning their usefulness in the lab.

                            I was only trying to raise the point that, while dummy loads are a very useful thing to have on the bench, still they do not reflect "real world" situations. In the real world if you want to get sound out of an amp you definitely need a speaker, not a dummy load, and a speaker behaves quite differently because of its nature and principle of operation; and to answer Bruce, there' s no denying that a dummy load is a perfect match while a speaker isn't, also, with a speaker we do have some losses a dummy load hasn't, so when measuring, some differences in the results are to be expected.

                            When I tested the TXs I had on the bench, the results with a dummy load were invariably better than the ones with a real antenna, still, if I wanted to broadcast something, I needed an antenna, not a dummy load. The same applies to amps, only the load nature changes, and the results I got using dummy loads always outclassed the ones I got using real speakers.

                            Think about testing an engine on the bench.....car manufacturers state power/torque and mileage with motors running on their labs' benches....how come the values we get out of our cars after buying them are invariably worse than the declared ones? Because we live ( and drive our cars ) in the real world and their testing is done outside of it.

                            Peace

                            Bob
                            Last edited by Robert M. Martinelli; 01-07-2009, 08:38 AM.
                            Hoc unum scio: me nihil scire.

                            Comment


                            • #44
                              I agree with everything you said Bob... my dummy loads, meters, scopes, books, charts and even AMPAGE ... all that crap... doesn't make one single useful sound! It's all about, "what sounds good... is good".
                              When vacuum tubes were still very common, right up to the very early 80's .... I was still working in the 2 way comm biz and did repairs, installations and certs on commercial TX, trunks, repeaters, police/fire/FBI and IRS mobiles, police radar junk, handhelds, pagers, etc... plus when I first started and just got my 1st Class Radio Telephone... the only job I could find was being the tower monkey installing arrays for the first year .... so how could I disagree?
                              Bruce

                              Mission Amps
                              Denver, CO. 80022
                              www.missionamps.com
                              303-955-2412

                              Comment


                              • #45
                                Originally posted by voxrules! View Post
                                Well,

                                On one hand I'm happy Bruce confirmed my thoughts about output power, tubes' life and about current production tubes, and I'm also happy ETR agreed that things are indeed different with a speaker.

                                On the other hand I think I have been misunderstood about the "dummy load" vs. "speaker" point I raised. I use dummy loads myself, and have done so also in other fields ( building transmitters and testing TXs output stages before connecting them to real antennas ), I think they're great and, if you want to compare "apples with apples" ( thanks ETR ) they're just fine, so I was absolutely not questioning their usefulness in the lab.

                                I was only trying to raise the point that, while dummy loads are a very useful thing to have on the bench, still they do not reflect "real world" situations. In the real world if you want to get sound out of an amp you definitely need a speaker, not a dummy load, and a speaker behaves quite differently because of its nature and principle of operation; and to answer Bruce, there' s no denying that a dummy load is a perfect match while a speaker isn't, also, with a speaker we do have some losses a dummy load hasn't, so when measuring, some differences in the results are to be expected.

                                When I tested the TXs I had on the bench, the results with a dummy load were invariably better than the ones with a real antenna, still, if I wanted to broadcast something, I needed an antenna, not a dummy load. The same applies to amps, only the load nature changes, and the results I got using dummy loads always outclassed the ones I got using real speakers.

                                Think about testing an engine on the bench.....car manufacturers state power/torque and mileage with motors running on their labs' benches....how come the values we get out of our cars after buying them are invariably worse than the declared ones? Because we live ( and drive our cars ) in the real world and their testing is done outside of it.

                                Peace

                                Bob
                                Using a dummy load is the only way that makes sense to do a direct comparison and is the industry standard. The back EMF a speaker's coil produces doesn't necessarily reduce power in a tube amp either, in fact I would say theres usually an overall increase in power especially on the rise of the waveform which can be seen quite easily on a scope. It's possible to measure the difference but it would be very difficult and you would have to figure in the impedance curve of the speaker and a bunch of other factors in the frequency/time domain. It would be meaningful only if everybody used the same speaker which of course we all don't so we all use resistive loads when measuring power. What would probably be more meaningful is to say what an amps average db output was with a given speaker/cab. But that still wouldn't tell you how much louder it would be in certain rooms or certain places within the room etc. So you have to eliminate variables if you want to do a direct comparison of a certain part of the picture such as the power section of a tube amp. That's why resistive loads are used.

                                Comment

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