1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Deuce is almost done

Discussion in 'Tube Audio' started by mjalazard, Aug 16, 2015.

  1. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
    This is a teaser. I had shown photos of my Citation II amp 3 years ago:
    http://www.audiokarma.org/forums/showthread.php?t=450402
    Many pointed out the flaws. Well, after over three patient years, the complete re-build of this amp is nearly complete. Full details and photos will come in a future thread. Here are some photos:
    2012: a hot mess
    [​IMG]

    I'll have updated photos soon

    Re-work of the back:

    [​IMG]

    More to follow :scratch2:
    Mike
     
    Last edited: Aug 19, 2015

     

    Please register to disable this ad.

  2. Westy56

    Westy56 A symphony of paradox

    Messages:
    6,612
    Location:
    Abq, NM
    Very nice.
    What pots did you go with for the bias?
    Did you change the AC balance pots too?
     
  3. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
    I'll have to defer all the detailed questions to AmpMedic. Phil is doing the complete rebuild including changes to accomodate the KT120 tubes from the original Carver "mod"
    Mike
     
  4. Dukiedook

    Dukiedook Super Member

    Messages:
    2,980
    Location:
    Mypos
    What kind of mods have to be done to accommodate KT120 tubes?
     
  5. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
  6. Westy56

    Westy56 A symphony of paradox

    Messages:
    6,612
    Location:
    Abq, NM
    Someone put an extra choke in it.
    The PS caps look much beefier size wise than the mcshane ones.
     

     

    Please register to disable this ad.

  7. vrusso123

    vrusso123 Well-Known Member

    Messages:
    588
    Location:
    Cleveland, Ohio
    Fabulous. got any specs?
     
  8. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
  9. pjfarano

    pjfarano 'AmpMedic'

    Messages:
    47
    Location:
    Henderson, NV 89014
    With the back of the Cit II facing down, there is a small Toroid trafo (McShane mod) on the right which now handles the pt bias and relieving the mains trafo of that duty.
    This amp also has the McShane Choke mod attached to the McShane Virtual Dual Mono mod.

    My hat is off to Jim McShane and Don Sachs for their generosity and guidance..

    In addition to the far right, is a filament trafo handling the voltage/current for the 6 signal tubes (Ampmedic mod). Because of the filament trafo, KT120's or KT88's can now be safely used, although you might have to change the cathode resistors on the pt's to 20 ohms for proper adjustment. These mods offload duties normally provided by the 57+ year old overheated mains trafo & help prevent failure.

    Both inputs are now on the channel 'B' side w/the original choke also moved to that side and again, the fila. trafo in place of the orig. choke location for a dead black background. The 60 cycle test output replaces the channel 'A' input position.

    All the grounds are 'star grounded' for a dead black background. Although more work, old tried-and-true habits die hard, LOL!

    I provided this Citation II with vent holes (1958's had NO VENT holes!) in the top of the chassis. I also drilled out additional holes in the bottom chassis cover. I removed the feet from the cover and installed thick-firm-felt to the circumference of the cover (see pics). The felt provides a seal to direct all powered ventilation (next paragraph) through the amp & not out the sides!...

    This amp now sits atop an adjustable speed, 4-fan Cool Components chassis cooler (Mike provided the cooler and also bought one for my Cit II.. Love you , Mike...) to provide low volume, almost noiseless at idle, power ventilation and remove the searing heat generated by the power resistors, tubes, etc.. If you have ever touched the chassis of an operating Cit II after 20 min., or have seen the scorched boards, you know what I mean.... CC fans set at 7.5 volts on the w/wart.

    I run my Cit II w/an additional almost noiseless at idle small, 2 speed fan (Wally World) placed in front (or back if you wish) to help keep the heat that accumulates in the mains trafo down to a comfortable level during a long session.

    The plate & cathode pin jacks are installed so as to remove the challenge of wrestling with this now 75 lb. monster in order to remove the cover to get the proper vdc readings for setup of this amp...

    I plan to make component changes to my boards in the future and will do the same for Mike's amp at no additional charge, as long as he continues to supply me with his to-die-for 'Banana Bread', LOL!
    (topped with ice cream, canned fruit & Reddi Whip... WOW!)

    The best to all of you,
    Ampmedic Audio Restorations
    Henderson, NV 89014
    702-560-1043
     
    Last edited: Oct 5, 2015
  10. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
    I owe Phil a lot of banana bread.
    Mike
     
  11. BillWojo

    BillWojo AK Subscriber Subscriber

    Messages:
    2,787
    Location:
    Burlington, NJ
    I'm curious what "the Carver mod" was all about.

    BillWojo
     

     

    Please register to disable this ad.

  12. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
    This is direct from Bob C's original listing:

    HOT-RODDED CITATION II POWER AMPLIFIER WITH 115 WATTS PER CHANNEL





    Hot-Rod

    Usually the expression “hot-rodded” sounds somewhat flip. However in this case, it evidences a remarkable new output stage combining Stu Hegeman's classic design and Mike Matthews’ new Tung-Sol KT120 output tube. This amplifier will come to you with Tung-Sol KT120's and 115 watts per channel, OR with Silver Eagle KT88's and 60 watts per channel. At the close of the auction, the choice will be yours.


    Remarkable New Tube

    Several months ago the new Tung-Sol KT120 vacuum tubes became available, and I just had to try them! I found them to be remarkable......no, great tubes with distortion, bandwidth, and fidelity as good as anything I have ever experienced. In order to obtain the best from these remarkable new tubes it was necessary to modify the turns ratio of the output transformer by a factor of 1.414. This lowered the impedance and optimally matched the new tubes, and I didn’t even have to alter the transformer design or change the wires inside; all I had to do was connect the external wires up in a new way such that the effective driving point impedance was optimized for these tubes.


    Success

    I was rewarded with a new and powerful amplifier that sounded as sweet and as expansive as it did prior to the hot-rodding, yet it easily outperformed the original amplifier.




    A Hot Mid-Summer’s Night


    It was a hot mid-summer's night and I was in Chicago at the consumer electronics show.

    I was in my booth pitching my wares, a new amp and preamp, and it was hot inside. Not the amplifier, but the convention floor, and I was getting thirsty. I wanted something cold to drink, so I decided to sneak away from my booth for a moment to get a coke. As I was sneaking, a colleague happened to walk by and said, " Hey Bob, have you seen Stu Hegeman's new preamp?"

    I found myself getting excited, as Stewart Hegeman, the master designer of so many classic vacuum tube amplifiers and my very own hero, was here! Stu Hegeman was a true genius, having designed the Citation I, II, probably the III and countless other amplifiers for Sidney Harmon and for Lafayette.

    We were just entering the solid state age, and Stu had started his own company to introduce his latest creation, the solid state Hapi I preamp. I just had to see it! So instead .of getting my coke, I made a bee-line to Hegeman's booth, and there I met the master and my hero. I introduced myself and HE said "I know who you are, you're the kid who designed the Phase Linear." Kid? Anyway, I was standing there mesmerized and in awe of my hero and could hardly concentrate on what he was saying, much less COMPREHEND what he was saying.

    And so we began talking about preamps and amplifiers, ultimately leading to a quiet corner in a close-by restaurant. Very close, as it was part of the convention itself. I finally got my coke. I could not believe I was in the presence of THE Stewart Hegeman, and he was talking to ME! We talked and talked about big solid state amps, tube preamps, solid state preamps, loudspeakers, ionic tweeters, recording lathes and finally tube power amps. And what a scientific talk it was! As the hours went by, he admitted to having been caught up in the ultra-linear fad of his day, that it was the biggest blunder of his career, and he did it only once and would NEVER design an amp with an ultra-linear output stage ever again.

    And he didn't. The Citation V was pure pentode, as was the subsequent Lafayette 550 and everything else he designed from then on. I asked why. He explained that when the plate pulls the top of the output transformer winding towards ground, the ultra-linear tap pushes the screen grid so low that it renders the tube unable to drive difficult loads. In addition, he pointed out that the normal idle potential on the screen grid regularly exceeded a safe voltage, often causing output tubes to blow up. The tube manufacturers hated it, but had to go along or lose market share, and so changed the specification for screen voltage in order to allow ultra-linear output stages. I can’t help but wonder if they REALLY changed the tube design, or simply changed the screen voltage specification.


    The Mighty 6550

    Back to Stu. Anyway, when I asked him about his favorite output tube, he said the mighty 6550 was the one to use, and when I queried about KT88's, he held up his little pinkie finger as if to hold a tea-cup and said in a mock British accent. " Brits you know, if you want watered down tea."

    He loved to use wide-band video pentodes in his amp designs, and did so when he could. (Read that as cost-no-object.) They were expensive then. "Why would anyone want to use a triode front-end when they could use a pentode?" he mused. Stu was single handily responsible for one of the worlds great amplifier topologies, the wide-band video pentode design. Never been done before, and it added a new category of stunning topologies to our universe.


    Back to Pure Pentode

    I’ve updated and modified this amplifier to represent an expression of Stu Hegeman’s latest thinking regarding power amplifier designs; it’s a way of thinking about amplifier designs that he was unable to implement for a variety of technical and political reasons. These modifications include a return to a pure pentode output stage, allowing substantially more output drive current than possible with, in his own words, the devil-begotten ultra-linear output stage. Strong words, but they were Stu’s. I don’t think Sidney Harman would have been pleased if he heard Stu saying that.


    Greater Energy Storage

    When Stu designed this amplifier, huge amounts of energy storage were not practical. He did the best he could with the available energy storage electrolytic capacitors of his day. In the vast intervening gulf of 50 years, the technology associated with capacitor energy storage has allowed an increase of approximately ten fold. This amplifier has had its energy storage increased substantially by the addition of HUGE capacitors that Stu could only dream about. This eliminates every last vestige of “DC bounce” on musical transients. DC bounce and low-frequency stability has always been the result of compromises made by Stu in order to design an amplifier for the real world, that could be BUILT in the real world. Not any more.


    Very Hot Output Tubes and The DC Restorer

    Stu talked about the need to run the output tubes extremely hot to get the distortion low enough to satisfy his boss, Sidney Harman. (The Citation division of Harman Kardon later relented on this point when too many output tubes began failing.) Consequently I had to invent a DC restorer circuit; it eliminated the troublesome need to idle each output tube at 50 watts ( ! ). This circuit allows the output stage to idle at approximately 12 watts per tube and retains the low distortion that Sidney wanted for his amplifiers. It works by keeping the DC component on each output tube grid the exact correct value through the entire audio signal swing, allowing perfect performance up to and even beyond clipping.


    Super Long-Lasting Output Tubes

    The DC restorer allows simultaneous low distortion and low idle power, allowing extreme longevity for the output tubes.

    The final distortion level in this amplifier is so low that I am embarrassed to write it down here.

    This amplifier will arrive with vintage GE 6550’s or KT88's, your choice. There is also a one year warranty, standard. If it ever breaks and you get it to me in the first year, I’ll fix it free of charge, and additionally I will give you a great deal if it EVER needs fixing.

    Features

    Four output terminals; common ground, four, eight and sixteen ohms. A bias meter, bias control and a balance control.

    One more thing: I accept ANY form of rational payment.

    The man with the big muscles is me, holding another amp inspired by Stu Hegeman's Citation-II

    Bob Carver

    MA
     
  13. Westy56

    Westy56 A symphony of paradox

    Messages:
    6,612
    Location:
    Abq, NM
    How does the "McShane Virtual Dual Mono mod" help with performance?
    I've only used his PS mods. The 10% better sounding claims on one of his other upgrades made me skeptical.

    I will give his PS upgrades a thumbs up for the novice owner because of the schematics and instructions included..
     
  14. pjfarano

    pjfarano 'AmpMedic'

    Messages:
    47
    Location:
    Henderson, NV 89014
    FR 2 cropped .jpg cropped from the back .jpg completed #2 .jpg
    As of 8/16, Dr. Mike's Citation II, along with my own, has now been completed. We are burning KT150 power tubes.

    The board components have been changed to match the components sold by Jim McShane.

    The Cit II now uses my improved power supply to safely wring the very best from KT120's or KT150's
    Yes, you can still use KT88's if you wish
    Installed are 2-105 degr. 10,000 hour caps/400 vdc doublers
    2-550 vdc 105 degr. 10,000 hr. caps, one for each output trafo (don't be fooled - these are proper 550vdc electrolytics and NOT 2-smaller caps in a larger shell. I opened the case for proof & have the pics)
    2-10,000 hr. 500 vdc caps, one for each board
    In addition, several new upgrades and modifications have been installed to facilitate using KT150's and to improve the original Cit II mains transformer shortcomings and to help it run cooler than stock.
    A new filament trafo has been installed to supply the 12BY7A signal & input tubes.
    The old bias supply has been disconnected. Installed are two high output individual toroid trafos, one for each channel w/improved electronics
    The B+ vdc has been increased by 26 volts
    A 20 second delay has been installed.
    Switches installed for triode/ultra-linear operation
    Last but not least, is the McShane/Sachs CCS circuit for each channel, complete with balancing pot for the signal tubes.
    After matching, adjustment & balancing of the signal tubes, the AC balance for each channel is set utilizing an oscilloscope...
    The grounding scheme has been improved.
    The amp is actually quieter now than the first build and dead quiet at idle and emits only a slight hiss (your ear needs to be within 3" or less of the speaker) when a preamp is attached

    This amp is not your daddy's or any body else's Citation II amp and will not disappoint.
    While still a very good power tube, the KT88 is no match for this KT150 Cit II.
    The proper build of this Cit II and using KT150's or KT120's will leave every other build in it's wake.
    It's that good...
     
    Last edited: Sep 29, 2016
  15. 70'sAudio

    70'sAudio Where it All Started for Me

    Messages:
    884
    Location:
    On The Golf Course
    WOW!! That's One Amazing Tube Amp On Steroids :yikes:

    Congrats to The AmpMedic for the Amazing Mods and Countless Hours of Work.

    Thanks For Sharing, Mike.
     
  16. mjalazard

    mjalazard Well-Known Member

    Messages:
    552
    Location:
    Las Vegas, baby!
    AmpMedic, Phil came by my house to listen to the upgraded Citation II in my system: Citation 1 upgraded by Sam Kim (http://www.samsaudiolabs.com); VPI HMW IV TT with JMW 10" tonearm and Ortofon Windfeld; Nakamichi mb 1000 transport; Oppo BPD 105 with the full ModWright mods used as the DAC (the Nak Transport is THAT GOOD);
    PS Audio NuWave Phono converter (while Phil upgrades my Sonic Frontiers SFP1 Sig); Magnepan 3.6R's with full Magnestand mods; a whole variety of Signal Cable wires.
    We spent a few hours listening to a variety of tunes in both triode and ultralinear modes. This damn amp drives the power-hungry maggies with ease. Everything is balanced and right. Dead quiet as well. Plenty of volume as well.
    I know there has been a lot of controversy regarding this amp re-build, but Phil really knows what he is doing. I'm happy and my Maggies are happy as well
    Mike
     

     

    Please register to disable this ad.

  17. pjfarano

    pjfarano 'AmpMedic'

    Messages:
    47
    Location:
    Henderson, NV 89014
    It should be noted that Mike's Citation II KT150 build was not the first of it's kind.

    The original Citation II KT150 prototype was completed for myself.

    All the mods were properly tested and run in for audio supremacy and reliability and auditioned by Michael in my own system so he could hear the improvements for himself before anything was done to his Cit II..!!!

    What's that, you say???


    That's Right:
    There was no road map for this restoration other than mods completed in other amplifiers and my own Cit II.

    So, it was completed in stages to improve the restoration to the client's satisfaction and provide value for Mike's investment so there would be NO BUYER'S REMORSE, as is sometimes the case for projects such as these, with the client being told "you need to break it in before you can hear the difference" (LOL!)...

    The only things that "break in" are your ears, as they become accustomed to your poor sounding components to justify the $$$'s you've thrown away..!!

    Absolute nonsense and never tolerated at AAR, Ampmedic Audio Restorations......


    Ciao bene,
    Ampmedic
    702-560-1043
     
    Last edited: May 6, 2017

Share This Page