[Roger A. Modjeski]

Not sure about the degree but he does know his stuff.  He is kind to send me his customers that need new tubes. He respects my testing methods and I have supplied him with tubes in the past.

[Doublej]

From the Amar Bose obituary published at the MIT News Office (newsoffice.mit.edu)

"Dr. Bose received his bachelor’s degree, master’s degree and doctorate from MIT, all in electrical engineering. He was asked to join the faculty in 1956, and he accepted with the intention of teaching for no more than two years. He continued as a member of the MIT faculty until 2001."

Steve

Steve,

I don't see the letters PhD in there do you? 

[JohnR]

Ok, this is silly. A doctorate IS a PhD. Or is there some finesse to the usual definition that you know about and are not telling?

[/mp]

A doctorate IS a PhD. Or is there some finesse to the usual definition that you know about and are not telling?

PhD : Doctorate :: poodle : dog.
All PhDs are doctorates; not all doctorates are PhDs.

[kenkirk]

Not sure about the degree but he does know his stuff.  He is kind to send me his customers that need new tubes. He respects my testing methods and I have supplied him with tubes in the past.

Yes I do believe Ken has an EE degree. Not positive but we spoke about it once. But case in point. The other day I flipped on my RM 10 MK II and after about 10 secs I heard a "pop" in the left channel speaker. Music came on but the left channel was dead. Now I have heard this happen before, many times over the years, with my Convergent Audio JL-1's. And I dread it! I have to wrestle a 200 pound amp out into the room, flip it over, remove 20 or so hex screws, take the bottom off. Find the burnt resistors, replace them, then check every resistor under each of the 8 tubes, put it all back together, replace the tube that caused the short, pray the new tube matches up close enough to balance the amp, drag back into position, hook up and play music again. But with the little RM-10 MK II I just replaced the little fuse next to the left channel EL 84's, reseated the tubes, fired it up and sat back and enjoyed the music. That is why I am such a believer in your circuit designs. And of course your amps sound wonderful too.

Ken

[Roger A. Modjeski]

Yes I do believe Ken has an EE degree. Not positive but we spoke about it once. But case in point. The other day I flipped on my RM 10 MK II and after about 10 secs I heard a "pop" in the left channel speaker. Music came on but the left channel was dead. Now I have heard this happen before, many times over the years, with my Convergent Audio JL-1's. And I dread it! I have to wrestle a 200 pound amp out into the room, flip it over, remove 20 or so hex screws, take the bottom off. Find the burnt resistors, replace them, then check every resistor under each of the 8 tubes, put it all back together, replace the tube that caused the short, pray the new tube matches up close enough to balance the amp, drag back into position, hook up and play music again. But with the little RM-10 MK II I just replaced the little fuse next to the left channel EL 84's, reseated the tubes, fired it up and sat back and enjoyed the music. That is why I am such a believer in your circuit designs. And of course your amps sound wonderful too.

Ken

Thanks, I do try to make things user friendly. Having started out at a radio/TV repair guy at age 16 I have seen a wide variety in the way products are put together. Fixing something should be easy and the most likely problems should be the easiest to repair. Thus the fuses are on top and there are no resistors to get burned up when a tube fails or blows off a little steam. Tubes are prone to lint shorts and other short lived phenomenon that draw high current briefly. If the fuse is adequate it will blow, the tube will recover and may not cause another problem for a long time. If a tube keeps blowing the same fuse just replace it when you have had enough of it. In my amps you can do this. in some amps you risk the very type of repair Ken describes on his CAT amp.

Many of you are reading the Tuning Fuse post (it is wildly popular) and perhaps have read how those fuses will not protect your tubes. To re-iterate: When a tube shorts a proper slow or fast blow fuse will blow rather quickly at some 200 mA because the potential current is several amps. If the fuse element turns to plasma, as it does in the Tuning Fuse, the plasma will continue to conduct several amps until the entire energy of the power supply is dumped into the tube and any components in its path. That means cathode resistors and the output transformer. I have seen an improper tube fuse cause an open in an RM-10 output transformer. I have seen improper fuses melt the fuse holder.

Tube fuses must always be high breaking. Amplifier makers know that, unfortunately the maker of Tuning Fuses gives no warning and reviewers in online magazines actually recommend them for tube fuses. It turns out that Tuning Fuses have even lower breaking ability than standard RadioShack fuses.

[kenkirk]

Thanks, I do try to make things user friendly. Having started out at a radio/TV repair guy at age 16 I have seen a wide variety in the way products are put together. Fixing something should be easy and the most likely problems should be the easiest to repair. Thus the fuses are on top and there are no resistors to get burned up when a tube fails or blows off a little steam. Tubes are prone to lint shorts and other short lived phenomenon that draw high current briefly. If the fuse is adequate it will blow, the tube will recover and may not cause another problem for a long time. If a tube keeps blowing the same fuse just replace it when you have had enough of it. In my amps you can do this. in some amps you risk the very type of repair Ken describes on his CAT amp.

You really can't over emphasize the value to the customer of a user friendly design in a tube product. I truly feel for the audiophile who graduates to his first tube amp but within a year is shipping a 100 plus pound beast across the country to have some resistors replaced. I grew up in the 60's and I played with tube amps and built tube kits. I have a decent test bench and I enjoy soldering and repairing tube gear. But I am not the norm for the hobby. Many guys just want to flip on the amp and enjoy the beautiful sound that tubes can make. Many spend over 10K on a high end tube amp. But tubes fail. That is what every one of them will do eventually. And if the design does not take that fact into consideration, the bottom panel will need to be removed exposing the customer to extremely high voltages. He needs to know a few things before he starts poking around in a high powered tube amp. If he does not know what he is doing, and is smart, he will find help. But the tube amp repair guys of the 60's are pretty much gone. So he goes back to his dealer, who promptly ships the amp off for repair of 20 cents worth of resistors and 100 bucks or more of shipping. And the poor guys has no stereo for a month or so. Its not hard to understand why these guys switch back to solid state after a few years. Roger is one of the few out there that gets this. Guys who have owned Music Reference tube amps for years have no idea what grief they have avoided. And others like me that have discovered these amps truly appreciate the designs for more than just the wonderful sound. Oh and another thing that irks me is the number of very expensive tube amps with the power tubes mounted to PC boards. Yuk. I guess the designers don't mind their 20K amps hitting the trash bin in 20 years, or less.

Ken

[Roger A. Modjeski]

Thanks Kenkirk,

A marketing guy once told me that I place too much emphasis on reliability and serviceability when speaking about how my products differ from others. His contention is that the purchaser is not thinking of what is going to happen down the road while he is enjoying that warm fuzzy feeling of having something new. For me part of the enjoyment of my music system is not having to fool with it. I just want to turn it on and enjoy it. If I buy an appliance, power tool, automobile I want something reliable. I don't want to waste my time fixing someone else's mistakes.

For a few clients I still do repairs on a variety of equipment that interest me. I see how things are being made these days. I charge not based on time alone but also difficulty. If something is easy to repair it is a joy to get it working again. If the maker has made it difficult I have to fight through his lack of consideration. Sometimes after fixing a difficult piece I have no energy left do to anything. There are several designers that, if I meet them at a show I will ask "Hey why did you make your equipment so hard to work on? Don't you have any consideration for the technician and owner that will have to pay for you not thinking of what happens down the road?"

I have had my hands on amplifiers from about every maker out there. After fixing them I take the opportunity to measure and listen to them. Oh, the stories I could tell.

I made the mistake of buying a used Maserati Bi-Turbo. Didn't cost much to buy but cost a lot to maintain. Had someone told me before I bought it what I was getting into I would have passed even if it was free. Just an oil change is a major event because you have to drop the sway bar to replace the filter. Adjusting the idle speed takes an hour. It was a pretty car, nice interior, good bodywork but a mechanical nightmare. I feared going on long trips and breaking down outside the reach of my mechanic. I traded it in for a Ford Mustang which has given me no trouble.

[/mp]

I don't want to waste my time fixing someone else's mistakes.
....
I [bought] a used Maserati Bi-Turbo.

Perhaps primed by your writing "automobile", the instant I read the first quoted sentence I imagined Ferrari. When I reached the latter, I thought same difference. 
As you're demoing a plasma speaker today, I'd like to take the opportunity to ask how it compares with electrostatic speakers? Fascinated by/Fantasize about plasmas since first learning of Dr. Hill's plasmatronics way back in high school; have a pair of electrostatics.

[Roger A. Modjeski]

Perhaps primed by your writing "automobile", the instant I read the first quoted sentence I imagined Ferrari. When I reached the latter, I thought same difference. 
As you're demoing a plasma speaker today, I'd like to take the opportunity to ask how it compares with electrostatic speakers? Fascinated by/Fantasize about plasmas since first learning of Dr. Hill's plasmatronics way back in high school; have a pair of electrostatics.

Currently my plasma speaker is suitable for parlor tricks. The demo went well. They really liked when I lit up a mercury vapor street lamp, got some nice plasma inside a clear incandescent lamp coming off the support points.

I had never driven it by an audio oscillator before. I was rather amazed at the SPL above 2 KHZ. Some were holding their ears. Right not its a rather impractical and dangerous thing to put into someones hands. However the signal to noise ratio is good, its pretty and certainly would impress people visually. Perhaps I will take it to a show for fun, if I ever go to one.

Dr Hill's plasma speaker required a 4 ft tall industrial cylinder of helium that had to be refilled rather often. My speaker just uses air, which is free.

[corndog71]

This is probably not related but I was reminded of this video which I thought you might enjoy.

http://youtu.be/2awbKQ2DLRE

[bdp24]

Before boutique "High End" (damn the day that term replaced the perfectly acceptable High Performance, because it references the price of a piece of gear, above and before all else. And it reeks of snobbery.) stores, Hi-Fi shops had an owner, if not an entire staff, who were technicians as well as sales persons. They came into the Hi-Fi business from the larger world of general electronics (many having learned the trade in WWII or Korea). When my ARC SP3 made a funny sound (and then no more sound) upon it's initial turn-on surge (why is did so is a topic for another day), the dealer I bought it from new took the pre-amp back to his work bench, found the problem, and replaced a blown resistor, all in about 5 minutes. If I were to buy a new piece of tube gear today, I would absolutely not do so from a store that would have to send a pre-amp or power amp back to the manufacturer to replace a resistor. That would be like sending a car back to the factory to replace a burned out light bulb because the dealer had no service department. Absolutely ridiculous!

[Roger A. Modjeski]

Before boutique "High End" (damn the day that term replaced the perfectly acceptable High Performance, because it references the price of a piece of gear, above and before all else. And it reeks of snobbery.) stores, Hi-Fi shops had an owner, if not an entire staff, who were technicians as well as sales persons. They came into the Hi-Fi business from the larger world of general electronics (many having learned the trade in WWII or Korea). When my ARC SP3 made a funny sound (and then no more sound) upon it's initial turn-on surge (why is did so is a topic for another day), the dealer I bought it from new took the pre-amp back to his work bench, found the problem, and replaced a blown resistor, all in about 5 minutes. If I were to buy a new piece of tube gear today, I would absolutely not do so from a store that would have to send a pre-amp or power amp back to the manufacturer to replace a resistor. That would be like sending a car back to the factory to replace a burned out light bulb because the dealer had no service department. Absolutely ridiculous!

Oh so true. Where have the in-store techs gone. Where are the techs at all? I recently rebuilt a Dynavector DV-8250and DV-3000 Gold preamp for a client of mine.These are rare pieces from the mid 1970s. Perhaps there was just one production run of 300-500 units as we have been told. My client likes to buy gear that is not working, have me fix it and keep (if he loves it) or resell it. These units had no tubes and had been stored in the closet for years. I could see that an attempt to repair them had been made previously without success. The previous owner had given up on them telling us that he could find no-one to work on them. Of course I considered it a great opportunity to fix and then get to play with them. It was an expensive, time consuming repair. If you know anyone who has these units or can get them at a good price, buy them and send them to me for repair. They are very good sounding pieces and pretty to look at. Really nice meters that light up too!

The power amp is an excellent 50 w/ch SEPP design. The preamp has inputs for three turntables, bass and treble and meters that read from milivolts to volts output in linear dB. That is a tricky thing to do. The meter lenses are beautiful beveled edge fine lead crystal glass. Knobs are gold plated.

https://www.google.com/search?q=dynavector+dv+3000+gold&rlz=1C1CHFX_enUS544US544&espv=2&tbm=isch&imgil=paH-njzqZzsB7M%253A%253Bhttps%253A%252F%252Fencrypted-tbn2.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcTpOsuIcAmrfCbGjcGKFMfWFYr9K7kaGFhVCbsqg4y3Nbuag13AJQ%253B684%253B496%253BAABSuUxEVSJK3M%253Bhttp%25253A%25252F%25252Faudio-heritage.jp%25252FDYNAVECTOR%25252Famp%25252Fdv-3000gold.html&source=iu&usg=__KA7wmcozXmX81RTBv-BF3RuD4T4%3D&sa=X&ei=LL3CU9WaDYnn8AHcrYGQDA&ved=0CCMQ9QEwAg&biw=1366&bih=600#facrc=_&imgdii=_&imgrc=-anWEY8SPZmcMM%253A%3BWkFpP61BHuOB3M%3Bhttp%253A%252F%252Fwww.tubeaudioproducts.com%252FEBAY%252Fdv3000gold%252Fdv1.jpg%3Bhttp%253A%252F%252Fwww.canuckaudiomart.com%252Fforum%252Fviewtopic.php%253Ff%253D4%2526t%253D12200%2526start%253D30%3B800%3B521

https://www.google.com/search?q=dynavector+dv+3000+gold&rlz=1C1CHFX_enUS544US544&espv=2&tbm=isch&imgil=paH-njzqZzsB7M%253A%253Bhttps%253A%252F%252Fencrypted-tbn2.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcTpOsuIcAmrfCbGjcGKFMfWFYr9K7kaGFhVCbsqg4y3Nbuag13AJQ%253B684%253B496%253BAABSuUxEVSJK3M%253Bhttp%25253A%25252F%25252Faudio-heritage.jp%25252FDYNAVECTOR%25252Famp%25252Fdv-3000gold.html&source=iu&usg=__KA7wmcozXmX81RTBv-BF3RuD4T4%3D&sa=X&ei=LL3CU9WaDYnn8AHcrYGQDA&ved=0CCMQ9QEwAg&biw=1366&bih=600#q=dynavector+dv+8250&tbm=isch&imgdii=_

[bdp24]

I don't know how a serious music lover can have a pre/integrated amp without at least a STEREO/MONO switch (if not the even better MODE switch). You HAVE to have a mono switch to play mono records, period. Unless you enjoy listening to the distortion produced from a Stereo cartridge playing the L-R modulations (I think they're called) in a mono groove. I don't, and I have a lot of Mono records. If you want a pure, no-switch signal path for your Audiophile records (how often do you listen to one of THOSE?), you can add on a Mode switch (Roger won't have to do any R & D before building you one ) to your system using a set of Tape In/Out jacks. There is a Scott Mode Switch box on eBay right now, but the guy wants $225 for it or I would have bought it. I offered him $50 (far more than it contains in parts. Plus, it's gotta be 50 years old.) for it when it was at $250, which he ignored. Or, do what I did: Have a second Pre with a Mode or Mono switch plugged into the Tape Out jacks on your main Pre, and for Mono records send the Tape Out signal from the main Pre into one of the high level inputs on the Mode switch Pre. Take the signal from the Main Output jacks of that Pre (the Mode switch is always after the tape out jacks in the circuit) and send it back to a high level input on your main Pre. The BEST way to play mono records, though, is to do as Art Dudley does-----a Mono only cartridge on a separate arm. That's a couple thousand bucks though. I'm working on it!

[Roger A. Modjeski]

A mono switch is pretty easy to make without using a second preamp. There need to be resistors on the L and R output so the channels will not fight each other and cause distortion. Usually 10K ohms is enough, use more if you like to the point that you loose some signal which might be good anyway.

We can easily make you a mono switch in our attenuator box and attenuate or not attenuate at the same time for $90. No research required.