No analog source, sorry. I have a better sound material but all from digital sources. Right now the weak point in my setup is the balanced 2x4 miniDSP which has always had a higher noise threshold than the unbalanced (probably a reason why they no longer offer it outside the 2x10Hd version). If there was no EQ on the speakers (by design) I would have made a fully passive Xover and use my dac built into the Oppo player which is quite good. But that is about as good as it gets in my audio chain.
I must say this amp is confusing me. Last night I listened to some material commonly labeled as "audiophile music". The performance after it warmed up was absolutely stunning. I did not feel the need to EQ anything. It takes the brain a while to adjust to appreciate some things. The dynamic range, the depth and the attack (not in deep bass but in mounting louder responses out from a quieter background) was extraordinary. I am guessing the intermodulation distortion is probably better than that of SS amps.
On the other hand, some other more common material (some previously mentioned), which I used to enjoy with my Pass design amps, now bothers me and I start thinking about the need to reEQ my audio chain.
So the amp is sort of growing on me. Only more time with it will tell.
The amp is keeping reasonably cool on one side where my (new) TV stand is open front to back. In the middle it runs hotter and the right side (closed on the back) also runs at a higher temp. Ideally the stand would be open front to back over the full width and the fan speeds could be reduced somewhat to further reduce their noise. The mid fan was also a different Noctua model than the other two and may merit revisiting to see if it is the most optimal choice.
As far as getting the max performance out of the amp: my friend is of the opinion that the cathode currents from the constant current source through R28 and R29 should be more important to be trimmed to balance, than the DC voltages off driver tube cathodes which I trimmed. I just followed what I measured on the other ("good") channel which worked right off the bat. Also I found that balancing the currents called for more turning of the trim pot which would probably run out of range available while those voltages could be trimmed to near identical. Not sure if the other channel had already been messed with before the amp came to me. I did not see any AR instructions as to how to trim the circuit. If someone has any info please feel free to share. Thx.
On the other hand, some other more common material (some previously mentioned), which I used to enjoy with my Pass design amps, now bothers me and I start thinking about the need to reEQ my audio chain.
So the amp is sort of growing on me. Only more time with it will tell.
The amp is keeping reasonably cool on one side where my (new) TV stand is open front to back. In the middle it runs hotter and the right side (closed on the back) also runs at a higher temp. Ideally the stand would be open front to back over the full width and the fan speeds could be reduced somewhat to further reduce their noise. The mid fan was also a different Noctua model than the other two and may merit revisiting to see if it is the most optimal choice.
As far as getting the max performance out of the amp: my friend is of the opinion that the cathode currents from the constant current source through R28 and R29 should be more important to be trimmed to balance, than the DC voltages off driver tube cathodes which I trimmed. I just followed what I measured on the other ("good") channel which worked right off the bat. Also I found that balancing the currents called for more turning of the trim pot which would probably run out of range available while those voltages could be trimmed to near identical. Not sure if the other channel had already been messed with before the amp came to me. I did not see any AR instructions as to how to trim the circuit. If someone has any info please feel free to share. Thx.
Understood. I may try then with my spectrum analyzer. My dac output is so so though, not the greatest signal to noise ratio, but I can also do true transfer function if I measure at dac output simultaneously. p.s. Some years back I considered making a super clean 1kHz source, contacted a professor, got a schematic from Harvard(or MIT?), but eventually did not want to spend the money on something I so rarely need 
Thanks again!
Thanks again!
as for the amp adjustment: I meant to load one channel at a time; would that do? to load both channels I have to see if I can borrow another dummy.
as for the socket: I did something like that when I got desperate and was just messing with it; inserting a tiny file and jiggling and pulling on the edges of the metal inserted in each pin hole. I have no idea what did it; right now it works and I am inclined not to touch it unless necessary. I hope the contact is Ok and is not impacting the sound quality. there is still a little noise left when I get ear close by the speaker but that could be anything. I wish I had more time to spend on the amp but my other projects are waiting.
Thanks guys for the notes.
as for the socket: I did something like that when I got desperate and was just messing with it; inserting a tiny file and jiggling and pulling on the edges of the metal inserted in each pin hole. I have no idea what did it; right now it works and I am inclined not to touch it unless necessary. I hope the contact is Ok and is not impacting the sound quality. there is still a little noise left when I get ear close by the speaker but that could be anything. I wish I had more time to spend on the amp but my other projects are waiting.
Thanks guys for the notes.
This weekend I got some time alone with the amp
I listened across a wide range of the material to tune my ear before I go in to reEQ my speakers. I wish I had the late Siegfried L. with me to hear his speakers with D150. He was not big on amps making a significant difference in sound, but he probably never heard his speakers with a tube amp since LX521s were always power hungry. I think with a proper EQ he would have been tempted to haul this monster to BAF and other places where he demoed his speaker designs.
As much as it pains me to say but trying to be objective, this amp is notably better than my other (classA SS) amps. E.g. there is something to be said about listening to blues on a tube amp, with the voice and the electric guitar up front and center (which probably explains why they use tubes in the Eguitar amps). I covered a range from Cuban music to French chansons, even numbers with accordion music and some music which draws on my ethnic background like Balkan Barcelona Orchestra.
The only issue I see with D150: it is THE connoisseur's amp. Some noted above that the source merited attention. I am not so sure about the analog vs. digital discussion, but the music material definitely needs to be carefully chosen for this amp. The way they record and mix sound on common material today definitely does not make for a good source for this amp.
Else, the only other thing is the industrial look which my wife noted. From a distance one would think it is a Soviet amp and not an American legend
I listened across a wide range of the material to tune my ear before I go in to reEQ my speakers. I wish I had the late Siegfried L. with me to hear his speakers with D150. He was not big on amps making a significant difference in sound, but he probably never heard his speakers with a tube amp since LX521s were always power hungry. I think with a proper EQ he would have been tempted to haul this monster to BAF and other places where he demoed his speaker designs.
As much as it pains me to say but trying to be objective, this amp is notably better than my other (classA SS) amps. E.g. there is something to be said about listening to blues on a tube amp, with the voice and the electric guitar up front and center (which probably explains why they use tubes in the Eguitar amps). I covered a range from Cuban music to French chansons, even numbers with accordion music and some music which draws on my ethnic background like Balkan Barcelona Orchestra.
The only issue I see with D150: it is THE connoisseur's amp. Some noted above that the source merited attention. I am not so sure about the analog vs. digital discussion, but the music material definitely needs to be carefully chosen for this amp. The way they record and mix sound on common material today definitely does not make for a good source for this amp.
Else, the only other thing is the industrial look which my wife noted. From a distance one would think it is a Soviet amp and not an American legend
that socket is still trouble. on turning on the buzz still comes and goes as the amp is warming up. last time I tapped lightly with hand just on top and it stopped (how ridiculous is that); so the issue is definitely a mechanical contact. After I have had a break and moved some of my other work forward I will pull the tube out again and try to clean the socket a little better, and maybe squeeze the inserted metal in the pin holes like ScottP suggested.
amp started acting up again. So I pulled it out, used deoxit on V4 base, and then poked around as suggested before. The latter backfired; now the springs are definitely shot and the tube is even looser than before. So I will have to order a new 9-pin base and replace the damn thing. The way it is going I think I will be much happier putting my SS amps back to work and tackling some other more satisfying project. This vintage monster will have to wait again.
and replace the damn thing. The way it is going I think I will be much happier putting my SS amps back to work and tackling some other more satisfying project. This vintage monster will have to wait again.finally changed the V4 base. Removing the old base was no issue since I could cut and crush it easily (I guess the material aged), so I was able to de-solder it pin by pin. What turned out to be the challenge was finding a base for the pattern. First I ordered replacements from China (before I desoldered the old one) and they came with legs on 18mm diameter whereas the holes on the board were on a 22mm circle. Then I ordered some nice Korean ones from tubestore in Canada and they came with legs on a 21mm circle but the legs at half length got really wide and could not fit the small holes , so I could not push the base all the way in. I did not feel like drilling out huge holes with such tiny traces on the back and a couple of small film caps right next to the holes.
Since I already spent $50 due to minimum order requirements and shipping etc. I bent the legs on the Chinese base but the pins were short (only half a millimeter out of holes on the other side), and the holes are not plated like on modern pcbs. I however decided to solder it in by trying to get the solder to follow each leg into the hole. The problem now is that the tube is a really tight fit into the new base which does not have much mechanical support if one was trying to pull the tube out. So I guess when I sell the amp this one may have to stay in for the shipping (unless I hold the base somehow when pulling the tube out but still risky for breaking the contacts).
I listened to the amp today. There is still some slight hum in the speaker, it comes and goes while the amp is worming up and then it settles at a level audible with ear close up; so if I was to keep it I would still probably chase that detail down to make it perfect, but at this point I want to move on with my usual projects (I already ordered material for a very interesting speaker to develop and I landed a pair of unobtanium power Jfets from Papa Pass himself, so the diy itch is getting stronger.
Here is the pic of the new base:
, so I could not push the base all the way in. I did not feel like drilling out huge holes with such tiny traces on the back and a couple of small film caps right next to the holes.Since I already spent $50 due to minimum order requirements and shipping etc. I bent the legs on the Chinese base but the pins were short (only half a millimeter out of holes on the other side), and the holes are not plated like on modern pcbs. I however decided to solder it in by trying to get the solder to follow each leg into the hole. The problem now is that the tube is a really tight fit into the new base which does not have much mechanical support if one was trying to pull the tube out. So I guess when I sell the amp this one may have to stay in for the shipping (unless I hold the base somehow when pulling the tube out but still risky for breaking the contacts).
I listened to the amp today. There is still some slight hum in the speaker, it comes and goes while the amp is worming up and then it settles at a level audible with ear close up; so if I was to keep it I would still probably chase that detail down to make it perfect, but at this point I want to move on with my usual projects (I already ordered material for a very interesting speaker to develop and I landed a pair of unobtanium power Jfets from Papa Pass himself
, so the diy itch is getting stronger.Here is the pic of the new base:
I am struggling to come up with a price for this vintage amp.
It is a one of a kind piece of audio history with a massive PS which no one today would make. I know I spend close to $2k on making a really good classA SS amp and I cannot make anything like this (as far as chassis and unobtanium tubes and transformers go). I traded a nice oscilloscope for it and in hindsight, if I knew that I would invest so much more money and time into refurbishing this monster, I should have either not acquired it or should have sold it in its vintage state and let the new owner struggle with it. Having said that, this is still my hobby and I got a taste of audio history and the experience counts.
Anyways, the amp now comes with balanced inputs, quiet Noctua fans in the same (CNC remachined) bracket, all electrolytic caps changed to the best grade, 8 (+1 spare) original GE 6550s matched by Audio Research for OS, 2 new Sovteks in grid regulator positions, with new rubber feet, with ~100$s in spare fuses, with a custom made Aluminum dolly, a bunch of spare 9-pin tube sockets, cleaned out contacts and fixed/checked out circuitry. I hope I did not forget anything (anyways it is all in the thread above).
The only thing I did not do was measure (and trim for minimum) distortion: I have an FFT analyzer but I do not have a very low noise sine generator to put the signal through. I contemplated making one some years ago but never invested into it.
The amp is very heavy so shipping is a killer. The tubes would probably have to ship separately; so would the original old parts if one wanted them.
I suggest to the new owner to have the space above the amp open and then add resistors to slow down the fans to bring the noise to an absolute minimum required for cooling. Right now they are maxed out on speed and if not obstructed on top the amp runs lukewarm.
Cosmetically: this thing came in an unbelievable condition. I broke a couple of tabs between the screws on the plastic block used for speaker binding posts (interestingly I saw the same in description of another D150 which was up for sale before); so the plastic ages and if you do not watch the spade terminal when tightening the screw, the spade can just crack the plastic barrier. You can see the sticker on top peeling off a bit and paint damaged only after removing the cover screws, else it is as good as it gets after 45 years (let us say 9/10).
I am going to say US$6k. (and I will not sit down to calculate my true costs since I do not want to ruin it for myself).
First post is here out of respect for the forum. I do not wish to sell to a reseller (so for those: please do not contact me) but to a true enthusiast since i got attached to this thing and I can appreciate the design intent behind making something that uses super matched parts and on top of it allows the end user to trim the bias.
If you are within a day of driving I would prefer you pick it up. (or we can meet half way if in Canada since taking it across the border would take a declaration and probably some cost).
I do not expect this thing to move quickly due to Covid but I am in no rush.
Thanks for all who supported me on this thread.
It is a one of a kind piece of audio history with a massive PS which no one today would make. I know I spend close to $2k on making a really good classA SS amp and I cannot make anything like this (as far as chassis and unobtanium tubes and transformers go). I traded a nice oscilloscope for it and in hindsight, if I knew that I would invest so much more money and time into refurbishing this monster, I should have either not acquired it or should have sold it in its vintage state and let the new owner struggle with it. Having said that, this is still my hobby and I got a taste of audio history and the experience counts
. Anyways, the amp now comes with balanced inputs, quiet Noctua fans in the same (CNC remachined) bracket, all electrolytic caps changed to the best grade, 8 (+1 spare) original GE 6550s matched by Audio Research for OS, 2 new Sovteks in grid regulator positions, with new rubber feet, with ~100$s in spare fuses, with a custom made Aluminum dolly, a bunch of spare 9-pin tube sockets, cleaned out contacts and fixed/checked out circuitry. I hope I did not forget anything (anyways it is all in the thread above).
The only thing I did not do was measure (and trim for minimum) distortion: I have an FFT analyzer but I do not have a very low noise sine generator to put the signal through. I contemplated making one some years ago but never invested into it.
The amp is very heavy so shipping is a killer. The tubes would probably have to ship separately; so would the original old parts if one wanted them.
I suggest to the new owner to have the space above the amp open and then add resistors to slow down the fans to bring the noise to an absolute minimum required for cooling. Right now they are maxed out on speed and if not obstructed on top the amp runs lukewarm.
Cosmetically: this thing came in an unbelievable condition. I broke a couple of tabs between the screws on the plastic block used for speaker binding posts (interestingly I saw the same in description of another D150 which was up for sale before); so the plastic ages and if you do not watch the spade terminal when tightening the screw, the spade can just crack the plastic barrier. You can see the sticker on top peeling off a bit and paint damaged only after removing the cover screws, else it is as good as it gets after 45 years (let us say 9/10).
I am going to say US$6k. (and I will not sit down to calculate my true costs since I do not want to ruin it for myself).
First post is here out of respect for the forum. I do not wish to sell to a reseller (so for those: please do not contact me) but to a true enthusiast since i got attached to this thing and I can appreciate the design intent behind making something that uses super matched parts and on top of it allows the end user to trim the bias.
If you are within a day of driving I would prefer you pick it up. (or we can meet half way if in Canada since taking it across the border would take a declaration and probably some cost).
I do not expect this thing to move quickly due to Covid but I am in no rush.
Thanks for all who supported me on this thread.
Last edited:
I will stay true to this post and keep everything regarding this amp out here:
Over the past months I have received most interest from people who strike me as resellers. They all start with no questions about the amp but are all about "willing to negotiate" etc.
As for the price comeback: they can order a matched pair of 300Bs (new WE production) at $1,499 and build an 8W/chan or something amp around it.
So my personal take on this: the fact that only 200 of these were made tells you that no one is meant to have an amp like that. I mean this is probably as much off the beaten path as it gets. Tube amps are not supposed to have transformers which can deliver 300W at peaks without saturation. It only happened that someone in the commercial realm at some point in time seems to have shared the passion for engineering for ultimate audio, hard to drive planar speakers of the time etc.
And only few of these are still around. This is one which came in a super shape. The worst thing about it was probably that it was not used enough and I had no previous tube experience (or patience) to work the tubes back in gradually so one arced when I initially just turned it on, you could see in the thread what all followed.
Over the past months I have received most interest from people who strike me as resellers. They all start with no questions about the amp but are all about "willing to negotiate" etc.
As for the price comeback: they can order a matched pair of 300Bs (new WE production) at $1,499 and build an 8W/chan or something amp around it.
So my personal take on this: the fact that only 200 of these were made tells you that no one is meant to have an amp like that. I mean this is probably as much off the beaten path as it gets. Tube amps are not supposed to have transformers which can deliver 300W at peaks without saturation. It only happened that someone in the commercial realm at some point in time seems to have shared the passion for engineering for ultimate audio, hard to drive planar speakers of the time etc.
And only few of these are still around. This is one which came in a super shape. The worst thing about it was probably that it was not used enough and I had no previous tube experience (or patience) to work the tubes back in gradually so one arced when I initially just turned it on, you could see in the thread what all followed.
40W/chan is sufficient on a lot of speakers. Though for me this usually means rms power in classA with peak power at twice as much. But say with Elsinores speakers that is exactly what I used. Later I made 100W/chan monoblocks for LX521s which have overdamped curvilinear cones and are not efficient being in an open baffle. Again, horses for races .
.In re: to the D150 amp:
the problem with this amp is that it is for THE audiophile but one who can afford it. I mean I saw one battered unit posted for parts for $2.4k. A new fully balanced successor amp from Audio Research is what? the cost is murderous. And D150 was what? $2.7k 45 years ago? then again, just start making amps and see what it all adds up to.
Another issue is that with vintage equipment like D150 one needs to be a tinkerer. A few asked me about how much it would still cost to bring the amp to a perfect shape: well you can tell me after you have done it.
At this point, all I know is that in my setup the amp is still making a very audible buzz which comes and goes while warming up. I kind of noticed that the buzz changes with those pingy noises the tubes sometimes make while warming up. Eventually it settles at a faint buzz audible with ear by the speakers and it is definitely noisier than my other amps. I will start turning it on more frequently to see if it improves with tubes getting worked in. Eventually one may need to check a few more things though. If I was a guy hooked on making one ideal setup in a dedicated listening room (which I do not have) and I wanted to turn my hobby into babysitting THE amp, I would probably keep this unit. But I already explained above my take on this hobby.
the problem with this amp is that it is for THE audiophile but one who can afford it. I mean I saw one battered unit posted for parts for $2.4k
. A new fully balanced successor amp from Audio Research is what? the cost is murderous. And D150 was what? $2.7k 45 years ago? then again, just start making amps and see what it all adds up to.Another issue is that with vintage equipment like D150 one needs to be a tinkerer. A few asked me about how much it would still cost to bring the amp to a perfect shape: well you can tell me after you have done it
.At this point, all I know is that in my setup the amp is still making a very audible buzz which comes and goes while warming up. I kind of noticed that the buzz changes with those pingy noises the tubes sometimes make while warming up. Eventually it settles at a faint buzz audible with ear by the speakers and it is definitely noisier than my other amps. I will start turning it on more frequently to see if it improves with tubes getting worked in. Eventually one may need to check a few more things though. If I was a guy hooked on making one ideal setup in a dedicated listening room (which I do not have) and I wanted to turn my hobby into babysitting THE amp, I would probably keep this unit. But I already explained above my take on this hobby.
Last edited:
for those who asked for pictures:
I thought there were enough in this thread but I can try to take more next time I pull it out of the TV stand. In the meantime this is the same unit when it was posted by my friend (with whom I traded later on). You can see it here in its original (untested) condition with a ton of dust (and some of his dog's hair too):
Audio Research D150 Photo #1469899 - Canuck Audio Mart
I thought there were enough in this thread but I can try to take more next time I pull it out of the TV stand. In the meantime this is the same unit when it was posted by my friend (with whom I traded later on). You can see it here in its original (untested) condition with a ton of dust (and some of his dog's hair too):
Audio Research D150 Photo #1469899 - Canuck Audio Mart
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.