I have one of these! But it's the LK-72 version. Fully restored, all JJ tubes. It sounds amazing! Anyone that says they don't like the sound of tube amps, or that tube amps do not have enough base, or not tight enough, etc. They have never heard one of these with some good speakers. I can crank this thing up full volume, no hiss, no hum, no audible distortion. But at just over half volume, it will run you out of the room and shake the walls. Great sound. Thanks for the video.
These are real jewels like a lot of vintage vacuum tube equipment, if they have been taken care of - and used - equipment that sets up for years and then brough out and put in service, often have issues with switches and controls simply because of non-use that can likely be solved with some cleaning and TLC. If we sat in the same chair for 25 years and then was expected to run a marathon, we would have a similar problem. 🙂 Thanks for your comments.
@ElPasoTubeAmps Exactly right. The analog potentiometers must be used and turned occasionally to keep them static free. Boo hoo, haha. I think this old equipment is well worth the little TLC it needs to kick the crap out of most solid state equipment. No comparison in sound quality in my humble opinion. I am a musician, I have played professionally, and I know what real sound is. Tube amps give me that lively sound that I get from a live performance. Don't really hear that from solid state equipment. Unless it has a tube preamp... Is the tubes that make the difference in the sound stage.
David; I believe you have a 299C there. Great amplifier. I have a 299B, which is the model that uses the 6BQ5/EL84 outputs and 6BL8 phase inverter/driver tubes. Those are fun amps for sure. They get a little cramped inside, but they work. Better to run them out of the cabinets for ventilation.
The 7591 JJs or the new Tungsol should fit but the vintage ones sound oh so good. When you check power and distortion on an integrated amp,do you go thru the preamp as well? I always go thru the preamp as well as the amp but I don't know if I'm getting the most accurate measurement or not.
Mike Samra If I am just testing the power amp section I drive the AUX (any high level) input. It is interesting that a good tube amp will do 0.5% THD and a top notch SS amp will do 0.005% and we often times prefer the tube amp. FR on these old Mac amps is amazing.
ElPaso TubeAmps I hear you,they are amazing..Another thing I wanted to mention on the Mac amps that is very critical and that is this..The .047uf caps in the phase inverter to voltage amp should be changed if they are the bumblebee type.They often crack and leak and even the slightest bit of DC leakage will cause the 12BH7 to run very hot and cook the 12K 2 watt resistors along with the 12BH7..I always change those out and put in either a Vitamin Q paper in oil or a Russian K40Y-9 paper in oil..You then want to change the 12K resistors to 12K 5 watt WW or CF because those 2 watt resistors do run hot and if you measure them,they always are about 12.7k to 13.2k but they are consistent with each other.That is the one place tho its best to use a paper in oil cap because the bumblebee is a wax paper cap and paper caps are very stable..You can use a film and foil but the pio is best. I will almost bet it will fix the bandwidth and lower signal to noise.That's one of those tricky ones.
You have asked a really good question. I see you have thought about it and know what you are asking. I don't want to make it too complicated but I need to say a few things. First off, to answer your question, an 8K transformer primary, from plate to plate, will measure 2K from plate to CT with an impedance bridge. That is a fact. What the plate load sees under signal drive, I am not sure of. I am going to guess 4K ohms. We know that inductors add in series just like resistors but inductors wound on the same core have a mutual inductance coupling factor of very close to 2. So, a transformer that measures, for example, 10H plate to plate will measure 1/4 that to the CT or 2.5H and the impedance value will follow. You really got me thinking about this. How would a dynamic measurement of current and voltage to determine impedance work out if this was measured? Probably mostly academic but worth finding out. We all like to work in the simpler RMS domain but reality exists in the peak level and signal-drive domain. If I can remember to get around to these measurements, I will let you know my results.
@@ElPasoTubeAmps Thanks!!! Well, I made a measurement, I placed two 4k resistors on each plate wire, I applied a 1khz voltage and I got the same voltage drop between the 4K resistor and the wires (center plate) so I think I reached a RMS value of 4k for each valve in class "B" it made me spend two days with a headache. heheh I know you don't understand Portuguese, but here is the moment 15min where I measure tensions dividing equally. ruclips.net/video/Rp_C48Zbu0g/видео.html
I have to ask. I have a restored one of these also. Would be be abnormal for the output transformers to run fairly hot? Say about 140F? This is running stepped down the 115V through a variac. Thanks in advance.
It is normal for the power transformer to run pretty hot - so hot you can't press and hold your hand on it after its been on a couple of hours. The output transformers should not get hot from current flowing through them but the output tubes are so close (that's why the metal shield is between the tubes and the transformers) they can get somewhat hot from the heat radiation from the output tubes.
Thank you for your reply. Do you think having the transformers at that temperature would cause any long term damage? My unit has no plate between the transformers and the tubes. But the Tung-Sol tubes I have leave a little gap.
I think it will be alright. Having your unit in a location where it can get some natural ventilation air flow is better rather than in a closed up console. If you do have it in a console where air flow is basically non-existent, as I do with my stereo equipment, I have installed a small and quite "muffin" type fan to move air around and it makes a tremendous difference. It doesn't require direct forced air cooling but just a gentle flow of air over equipment will lower the temperature significantly and especially so with vacuum tubes.
I always see the Triplett 630-pl hanging on your wall. I just bought a very clean one on ebay for 40 bucks, I am going to compare it to my Simpson meters and see which one I want to keep, I have the 260 series 6. I really like it but it wont to the 5000v like the Triplett. Your thoughts?
Hi James, Throughout my career, there were two camps concerning the Triplett and Simpson meters. Seems most preferred the Simpson maybe because it's a bit smaller and simpler (?) I used both in my work for 26 years as a tech for NASA and WSMR and both are great instruments. I still use them 45 years later from the beginning (and end) of that career. As you mentioned, the model 630-PL does 5 Kv and the 630-NA does 6 Kv. The Triplett also has a Rx100K scale... but... they use a goofy 30 volt battery that is expensive and doesn't last long nowadays. I have never personally owned a Simpson 260 but I love both instruments equally. The HV scale on the Triplett has come in handy for me on several occasions as I have built several instruments that run in the 3-4 Kv range. Keep both your Simpson and Triplett. I have seen the Rx1 scale blown out of both instruments several times from measuring AC on the ohms scale or a real inexperienced tech rotating the selector switch through its range while connected to a power supply. Same result every time. :-) One of my friends that worked at WSMR with me, employed by Lockheed, once went into the UPS room (Big UPS rooms...) and somehow got his Simpson 260 across the HV line input to the power company transformers. Don't know the exact voltage but many thousands of volts and, as he tells the story, the hair on the back of his neck stood up from the HV charge and suddenly it arced across his 260 exploding it and throwing shrapnel into his face guard (thank God he was using one) and embedding more chunks into his gloves, clothing and skin. He came out of the ordeal with not too much injury but it could have turned out much different.
I love the Simpson, and yes I think I will keep both. I just wanted a meter I could check plate voltage with and no have to use a hi voltage probe. I have read that the Triplett is a little more accurate, although my Simpson tracks identical to all three of my Flukes. Thanks for your reply and keep those videos coming. I am working on a Musicman driver board as we speak.
I received my Triplett 630 PL from a seller on ebay today. I am in love! It is a thing of beauty, not a scratch on it. Just need a 30v battery. It dwarfs my Simpson 260-5.
Hello David! How are you doing? I see you're using the AA501. Interesting piece of test equipment! Might be worth my while to try & hunt one down. One question...How accurate is it? I'm asking because I'd like to beef up my test gear a little more. I have an excellent HP audio oscillator, but this is something that would be valuable and a time saver for me. I see quite a few of those tall & husky 7591's around. One of the things that I don't like about the Sovteks is the shallow base. I picture the cement drying up from the heat and the bases becoming loose eventually. Most of the re-issues have the 6L6 style glass envelopes. Hope you're doing well. I keep in touch with Uncle Doug on Facebook. He's a good egg! :) Stay well & keep in touch. Frank--Audio Craft Electronics. :)
Hi Frank - all is well here - I hope you and your loved ones are doing well. From my opinion, the AA501 is the last word in audio analysis that I can afford. It is microprocessor controlled but still a bit like a high precision one shot bolt action rifle. The HP 8903 is a fantastic instrument and can do so many things that the AA501 cannot. I have had an in depth discussion (which is mostly experience and opinion) about the accuracy and direct comparison of the THD readings on the AA501 and the 8903 with another gentleman that owns and uses both that lives in Ohio. In my experience and his, we agree that if you use the signal source from the 8903, then both the 8903 and the AA501 will eventually agree on THD (after 30 seconds or so) but if you use an external source like the SG505, they sometimes have a much harder time agreeing precisely. I hold the SG505 as the “top dog” of audio oscillator at 0.0008 (8 ppm) THD - and under the best of conditions, the AA501 and SG505 will meet these Tektronix specs. With all that said, how good can we expect life to be? We are not an NIST lab but unbelievable, we can own instruments of this class - I still find it hard to believe. So… I would fight to keep both the AA501 and 8903 but (back to the bolt action rifle) if I could only have one, I think I would take the AA501. I have also been told that the design of the AA501 is a bit simpler (less stages) than the 8903 which (seemingly) makes it less susceptible to distortion and anomalies. I can’t get through a day without both of these instruments I hear you with your concern about the base on the Sovteks. Doug and I went to Las Cruces last week together and had a good long time for discussions. I always enjoy his company and conversation. Another subject on my mind are SET amps. Do you have any experience with them?
I've recently (a month ago) repaired an SET power amp that was a push-pull design using 2 EL84/6BQ5's. Puts out about 2-1/2 watts (I no longer use the acronym RMS--as you know, that's a whole other story). The one I worked on used a 5U4G for a rectifier, It requires a 2 volt input signal for it to give it's all. The biasing circuit is of the self- bias design, which I'm not fond of. It's supposed to be designed that if you put a set of unbalanced tubes, they're supposed to balance out. Well, it's a lot of horse poop. I had problems with one of the 6BQ5's red-plating a good amount. I had to swap around a few tubes to get 2 that were matched...all turned out well after that. One of the things that is great about them is, they're made in the good 'ol USA!!! A miracle these days of out-sourcing. Another interesting thing that I found out (unfortunately after the customer paid me for the repair was, they have a life-time warranty. This was the first SET I've ever worked on. Nicely made amp. I'm going to try & get a library of schematics for some of their popular models to keep on hand. If I score them, I'll gladly send you the PDF's to keep in your library. :)
If you test the THD at just 8Watts, what you expect...? Anything above 1% will be indicate a faulty amp or some wrong bias settings, as this unit is intended for HiFi use. ;) Anyway, very good video, thanx for sharing your test results!!!
TubiCal I agree with you that I "went easy" on the amp and did not stress it to its max power but it actually performs better than the Dynaco Mark III at the same 8-10 watt level - better at 20 Hz and especially better at the higher frequencies - considerably flatter.
It´s based on its design center values. I don´t know may of the great american tube days Amps, but i know some from germany, and they do have the same "characteristica" sometimes. Take the "braun CSV-60" it has 2 times PL-504 (or PL-500) output tubes PP/ch and delivers just 30Watts per channel. On the other hand take a 2 times EL84 Amp some rated 15Watts. To deliver this with two EL84 PP/ch you have to push them and you got no margins for a feedback loop. So THD would be (and is) much worse. Next is the overall quality of the output tranny(s). You need a lot of knowledge to wind some good ones. YOu need a lot of primary inductance to have good performance at low frequencies, or the core will go into saturation even at low SPL. That´s where we need to divide the HiFi and the intromentation world again. Look at a 100W marshall head, and take a close look to its OPT just nearly half the mass of the power tranny. It just can´t deliver much undistorted SPL, but this is *intended*. On the other hand, look at the OPT of a laney 100W head. That OPT uses the same iron size as its power tranny. Resulting in a way more cleaner, precise sound with very low distortion undless you push it really hard. Next if you ever seen some good HiFi OTPs rated for 100W, you know that´s a complete different buisness. They use an EI-130a cores and for 50W usual M102 cores. Here is a table where you can see diferent cores vs. power handling capa. (ok it´s german, but the figures/readings should be international anyway;) www.roehrenkramladen.de/Trafowickelmaschine/Twm3.html
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I have one of these! But it's the LK-72 version. Fully restored, all JJ tubes. It sounds amazing! Anyone that says they don't like the sound of tube amps, or that tube amps do not have enough base, or not tight enough, etc. They have never heard one of these with some good speakers. I can crank this thing up full volume, no hiss, no hum, no audible distortion. But at just over half volume, it will run you out of the room and shake the walls. Great sound. Thanks for the video.
These are real jewels like a lot of vintage vacuum tube equipment, if they have been taken care of - and used - equipment that sets up for years and then brough out and put in service, often have issues with switches and controls simply because of non-use that can likely be solved with some cleaning and TLC. If we sat in the same chair for 25 years and then was expected to run a marathon, we would have a similar problem. 🙂 Thanks for your comments.
@ElPasoTubeAmps Exactly right. The analog potentiometers must be used and turned occasionally to keep them static free. Boo hoo, haha. I think this old equipment is well worth the little TLC it needs to kick the crap out of most solid state equipment. No comparison in sound quality in my humble opinion. I am a musician, I have played professionally, and I know what real sound is. Tube amps give me that lively sound that I get from a live performance. Don't really hear that from solid state equipment. Unless it has a tube preamp... Is the tubes that make the difference in the sound stage.
David; I believe you have a 299C there. Great amplifier. I have a 299B, which is the model that uses the 6BQ5/EL84 outputs and 6BL8 phase inverter/driver tubes. Those are fun amps for sure. They get a little cramped inside, but they work. Better to run them out of the cabinets for ventilation.
The 7591 JJs or the new Tungsol should fit but the vintage ones sound oh so good. When you check power and distortion on an integrated amp,do you go thru the preamp as well? I always go thru the preamp as well as the amp but I don't know if I'm getting the most accurate measurement or not.
Mike Samra If I am just testing the power amp section I drive the AUX (any high level) input. It is interesting that a good tube amp will do 0.5% THD and a top notch SS amp will do 0.005% and we often times prefer the tube amp. FR on these old Mac amps is amazing.
ElPaso TubeAmps
I hear you,they are amazing..Another thing I wanted to mention on the Mac amps that is very critical and that is this..The .047uf caps in the phase inverter to voltage amp should be changed if they are the bumblebee type.They often crack and leak and even the slightest bit of DC leakage will cause the 12BH7 to run very hot and cook the 12K 2 watt resistors along with the 12BH7..I always change those out and put in either a Vitamin Q paper in oil or a Russian K40Y-9 paper in oil..You then want to change the 12K resistors to 12K 5 watt WW or CF because those 2 watt resistors do run hot and if you measure them,they always are about 12.7k to 13.2k but they are consistent with each other.That is the one place tho its best to use a paper in oil cap because the bumblebee is a wax paper cap and paper caps are very stable..You can use a film and foil but the pio is best. I will almost bet it will fix the bandwidth and lower signal to noise.That's one of those tricky ones.
Thanks for the videos! ELPasso asks a question: an el84 push pull on an 8kohms PP transformer, what load does each valve face 2k or 4kohms?
You have asked a really good question. I see you have thought about it and know what you are asking. I don't want to make it too complicated but I need to say a few things. First off, to answer your question, an 8K transformer primary, from plate to plate, will measure 2K from plate to CT with an impedance bridge. That is a fact. What the plate load sees under signal drive, I am not sure of. I am going to guess 4K ohms.
We know that inductors add in series just like resistors but inductors wound on the same core have a mutual inductance coupling factor of very close to 2. So, a transformer that measures, for example, 10H plate to plate will measure 1/4 that to the CT or 2.5H and the impedance value will follow.
You really got me thinking about this. How would a dynamic measurement of current and voltage to determine impedance work out if this was measured? Probably mostly academic but worth finding out. We all like to work in the simpler RMS domain but reality exists in the peak level and signal-drive domain. If I can remember to get around to these measurements, I will let you know my results.
@@ElPasoTubeAmps
Thanks!!! Well, I made a measurement, I placed two 4k resistors on each plate wire, I applied a 1khz voltage and I got the same voltage drop between the 4K resistor and the wires (center plate) so I think I reached a RMS value of 4k for each valve in class "B" it made me spend two days with a headache. heheh
I know you don't understand Portuguese, but here is the moment 15min where I measure tensions dividing equally. ruclips.net/video/Rp_C48Zbu0g/видео.html
I have to ask. I have a restored one of these also. Would be be abnormal for the output transformers to run fairly hot? Say about 140F? This is running stepped down the 115V through a variac. Thanks in advance.
It is normal for the power transformer to run pretty hot - so hot you can't press and hold your hand on it after its been on a couple of hours. The output transformers should not get hot from current flowing through them but the output tubes are so close (that's why the metal shield is between the tubes and the transformers) they can get somewhat hot from the heat radiation from the output tubes.
Thank you for your reply. Do you think having the transformers at that temperature would cause any long term damage? My unit has no plate between the transformers and the tubes. But the Tung-Sol tubes I have leave a little gap.
I think it will be alright. Having your unit in a location where it can get some natural ventilation air flow is better rather than in a closed up console. If you do have it in a console where air flow is basically non-existent, as I do with my stereo equipment, I have installed a small and quite "muffin" type fan to move air around and it makes a tremendous difference. It doesn't require direct forced air cooling but just a gentle flow of air over equipment will lower the temperature significantly and especially so with vacuum tubes.
Mine gets pretty warm also, but it does not affect performance.
I always see the Triplett 630-pl hanging on your wall. I just bought a very clean one on ebay for 40 bucks, I am going to compare it to my Simpson meters and see which one I want to keep, I have the 260 series 6. I really like it but it wont to the 5000v like the Triplett. Your thoughts?
Hi James, Throughout my career, there were two camps concerning the Triplett and Simpson meters. Seems most preferred the Simpson maybe because it's a bit smaller and simpler (?) I used both in my work for 26 years as a tech for NASA and WSMR and both are great instruments. I still use them 45 years later from the beginning (and end) of that career. As you mentioned, the model 630-PL does 5 Kv and the 630-NA does 6 Kv. The Triplett also has a Rx100K scale... but... they use a goofy 30 volt battery that is expensive and doesn't last long nowadays. I have never personally owned a Simpson 260 but I love both instruments equally. The HV scale on the Triplett has come in handy for me on several occasions as I have built several instruments that run in the 3-4 Kv range. Keep both your Simpson and Triplett. I have seen the Rx1 scale blown out of both instruments several times from measuring AC on the ohms scale or a real inexperienced tech rotating the selector switch through its range while connected to a power supply. Same result every time. :-)
One of my friends that worked at WSMR with me, employed by Lockheed, once went into the UPS room (Big UPS rooms...) and somehow got his Simpson 260 across the HV line input to the power company transformers. Don't know the exact voltage but many thousands of volts and, as he tells the story, the hair on the back of his neck stood up from the HV charge and suddenly it arced across his 260 exploding it and throwing shrapnel into his face guard (thank God he was using one) and embedding more chunks into his gloves, clothing and skin. He came out of the ordeal with not too much injury but it could have turned out much different.
I love the Simpson, and yes I think I will keep both. I just wanted a meter I could check plate voltage with and no have to use a hi voltage probe. I have read that the Triplett is a little more accurate, although my Simpson tracks identical to all three of my Flukes. Thanks for your reply and keep those videos coming. I am working on a Musicman driver board as we speak.
I received my Triplett 630 PL from a seller on ebay today. I am in love! It is a thing of beauty, not a scratch on it. Just need a 30v battery. It dwarfs my Simpson 260-5.
Hello David! How are you doing? I see you're using the AA501. Interesting piece of test equipment! Might be worth my while to try & hunt one down. One question...How accurate is it? I'm asking because I'd like to beef up my test gear a little more. I have an excellent HP audio oscillator, but this is something that would be valuable and a time saver for me. I see quite a few of those tall & husky 7591's around. One of the things that I don't like about the Sovteks is the shallow base. I picture the cement drying up from the heat and the bases becoming loose eventually. Most of the re-issues have the 6L6 style glass envelopes. Hope you're doing well. I keep in touch with Uncle Doug on Facebook. He's a good egg! :) Stay well & keep in touch. Frank--Audio Craft Electronics. :)
Hi Frank - all is well here - I hope you and your loved ones are doing well.
From my opinion, the AA501 is the last word in audio analysis that I can afford. It is microprocessor controlled but still a bit like a high precision one shot bolt action rifle. The HP 8903 is a fantastic instrument and can do so many things that the AA501 cannot. I have had an in depth discussion (which is mostly experience and opinion) about the accuracy and direct comparison of the THD readings on the AA501 and the 8903 with another gentleman that owns and uses both that lives in Ohio. In my experience and his, we agree that if you use the signal source from the 8903, then both the 8903 and the AA501 will eventually agree on THD (after 30 seconds or so) but if you use an external source like the SG505, they sometimes have a much harder time agreeing precisely. I hold the SG505 as the “top dog” of audio oscillator at 0.0008 (8 ppm) THD - and under the best of conditions, the AA501 and SG505 will meet these Tektronix specs. With all that said, how good can we expect life to be? We are not an NIST lab but unbelievable, we can own instruments of this class - I still find it hard to believe. So… I would fight to keep both the AA501 and 8903 but (back to the bolt action rifle) if I could only have one, I think I would take the AA501. I have also been told that the design of the AA501 is a bit simpler (less stages) than the 8903 which (seemingly) makes it less susceptible to distortion and anomalies. I can’t get through a day without both of these instruments I hear you with your concern about the base on the Sovteks. Doug and I went to Las Cruces last week together and had a good long time for discussions. I always enjoy his company and conversation.
Another subject on my mind are SET amps. Do you have any experience with them?
I've recently (a month ago) repaired an SET power amp that was a push-pull design using 2 EL84/6BQ5's. Puts out about 2-1/2 watts (I no longer use the acronym RMS--as you know, that's a whole other story). The one I worked on used a 5U4G for a rectifier, It requires a 2 volt input signal for it to give it's all. The biasing circuit is of the self- bias design, which I'm not fond of. It's supposed to be designed that if you put a set of unbalanced tubes, they're supposed to balance out. Well, it's a lot of horse poop. I had problems with one of the 6BQ5's red-plating a good amount. I had to swap around a few tubes to get 2 that were matched...all turned out well after that. One of the things that is great about them is, they're made in the good 'ol USA!!! A miracle these days of out-sourcing. Another interesting thing that I found out (unfortunately after the customer paid me for the repair was, they have a life-time warranty. This was the first SET I've ever worked on. Nicely made amp. I'm going to try & get a library of schematics for some of their popular models to keep on hand. If I score them, I'll gladly send you the PDF's to keep in your library. :)
If you test the THD at just 8Watts, what you expect...? Anything above 1% will be indicate a faulty amp or some wrong bias settings, as this unit is intended for HiFi use. ;)
Anyway, very good video, thanx for sharing your test results!!!
TubiCal I agree with you that I "went easy" on the amp and did not stress it to its max power but it actually performs better than the Dynaco Mark III at the same 8-10 watt level - better at 20 Hz and especially better at the higher frequencies - considerably flatter.
It´s based on its design center values. I don´t know may of the great american tube days Amps, but i know some from germany, and they do have the same "characteristica" sometimes. Take the "braun CSV-60" it has 2 times PL-504 (or PL-500) output tubes PP/ch and delivers just 30Watts per channel.
On the other hand take a 2 times EL84 Amp some rated 15Watts. To deliver this with two EL84 PP/ch you have to push them and you got no margins for a feedback loop. So THD would be (and is) much worse.
Next is the overall quality of the output tranny(s). You need a lot of knowledge to wind some good ones. YOu need a lot of primary inductance to have good performance at low frequencies, or the core will go into saturation even at low SPL.
That´s where we need to divide the HiFi and the intromentation world again.
Look at a 100W marshall head, and take a close look to its OPT just nearly half the mass of the power tranny. It just can´t deliver much undistorted SPL, but this is *intended*.
On the other hand, look at the OPT of a laney 100W head. That OPT uses the same iron size as its power tranny. Resulting in a way more cleaner, precise sound with very low distortion undless you push it really hard.
Next if you ever seen some good HiFi OTPs rated for 100W, you know that´s a complete different buisness. They use an EI-130a cores and for 50W usual M102 cores.
Here is a table where you can see diferent cores vs. power handling capa. (ok it´s german, but the figures/readings should be international anyway;)
www.roehrenkramladen.de/Trafowickelmaschine/Twm3.html
Fantastic'