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Jeffrey D. Medwin

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Everything posted by Jeffrey D. Medwin

  1. No doubt. Most likely. the passive crossovers you used were typical, and thus FAR from idealized as to wiring and parts choices and implementation. IF ( a big word ) a passive crossover is well done, and you run great electronics, a Passive will be an improvement over an Active, because the Active calls for a whole other set of gain stages, in the crossover, to do that signal dividing. That " always at least one other gain stage ", ( with passive parts inserted to get the roll offs ), gets 'ya. IMHO, IME, the extra gain stage employed, be it tube or sold state, creates a lack of transparency, in a really superbly implemented audio system. I am referring to a system that is at the edges of state-of-the-art, in the high-efficiency audio world. KISS often rules. As an example, I use a two way speaker, and absolutely NO crossover at all ...........on the 15 inch woofer. It is now directly amp - driven, ....runs full range. I almost never see a Passive crossover I really like, however. So the conceptually-inferior Actives can sneak into use. YMMV, fine, its all IMHO. Jeff Medwin
  2. You are correct. Dual plate ( bi-plate ) 2A3s are at best, mid-fi in performance. A single plate 2A3 version will outperform them, IF they have a linear "harp" filament structure , because it avoids a filament emission in a "Vee" or a " W " shape - an uneven / non-symmetrical ( non-linear ) emission source. The flaws I hear in a ST 45 DHT triode will not be determined properly in any amp such as an ordinary Yamomoto A-08. I know this from doing direct amplifier comparisons - with an friend's A-08. Our listening was done with his A-08, in 2015, versus a substantially higher-performing amplifier circuit, as described on this Forum in the KT88 thread. One can review that two-amp commentary, in the May 8th post on page 8, under the paragraph entitled " Clue Number five ". https://community.klipsch.com/index.php?/topic/182623-kt88-direct-coupled-design/page/8/ Have a great Black Friday shopping day !! Jeffrey Medwin
  3. Not to be be cheeky, but to my best knowledge, there was absolutely no problem with the DC amps, the speaker, or the room. ' Just the opposite occurred. My system performs now at a level where it can mercilessly expose the flaws of the Type 45 ST tube itself, easily, and precisely - just as it was described above ! I subsequently sold-off my entire TYPE 45 ST collection on eBay. YMMV, fine with me !! Jeff
  4. Well !! You are right. Everything matters. But I would think the materials composition / construction of a resistor might sport a ten-to-one added effect over solder or tolerance. That, is just only a guess. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Next, the BadChile poster needs to try TWO of those PRPs at double the Ohmic Value, matched to each other by 0.1% or better, on the plate ( anode) of his amp's input tube. See if that doesn't sound better, richer in the lower mids, more dynamic on pulsed piano notes and focused. Why ?? You have created two paths for the signal to travel through, tight matching precludes skewing, and the doubled-up paths have a better signal transfer efficiency. This is a technique first used commercially by the ultra rare and highly regarded MFA ( Moore Franklin Associates ) multi-chassis Luminescence preamp, of the ? 1970s?? Unaware of a "Lumi", see this URL : https://forum.audiogon.com/discussions/mfa-luminescence-mc-reference-preamp I try to use this obscure doubled-up, tightly-matched ( usually with 2 Watt ) resistor technique in almost all I DIY build for my own use, in 2019. BadChile next - needs to try it, in just that one sensitive circuit position, even with his 1/2 Watt resistors, he will likely hear it !! A partial-assembly photo , ( taken 6-23-19 ) shows both channel's Input / Driver tube - with doubled-up Ra and Rk : MFA phono preamp below : LOOK at all their paralleled 2 Watt resistors, and a 4 Watt metal film, on the plate of the input tube. Also tripled-up resistors, 2 Watt, on cathodes !! Bruce Moore and Scott Franklin knew back then - what sounded great, and they incorporated it into their commercial audio products !! I have had two people say to me " it was the best phono stage ever made. " You should see their Power Supply schematic !! Jeffrey Medwin
  5. Myself, and many many others, have found every component inside an amplifier imparts its signature on to the resultant sound,..... every part !! That is why some design amps and build by ear, not by test gear. That is one reason why we use high efficiency speaker systems, because it TELLS you right away, what a parts change has done, while operating at perhaps only 1/4 of a watt !! Its sensitive - puts it " right in your face ". But this thread is getting off track ! Jeffrey Medwin
  6. Or maybe better yet, than any MC275, or those denoted above - a pair of MC 60 monoblocks, because of their dual 5U4GB rectifiers. ( mono plus dual rectifiers, the only consumer model - built like that ). - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - The front end of all these Mac amps is FAR too complex IMHO. They need to use one less stage, they need to be modified.. I think there is probably better Push Pull tube amps today, performance - wise, than a McIntosh !! I say this mainly because modern designers typically do today's Push Pull circuit with less parts / less stages / mainly so as to less-degrade the signal. MechEng Vic reports this in his own post, his own direct listening reactions, just above this post.. This is JUST " my " opinion. You may have a different one. That - is totally fine !! Jeff Medwin
  7. You might be right about that !! But whenever I remove NFB loops from decently made triode amps, they sound more natural, have better PRAT, and do not sound like you are listening to an amp at all, (which 98% do, unfortunately, sound like) but rather, like you are hearing the music directly. ie, we can HEAR the feedback applied...as un natural. I am not the only one in this world who hears this, many many good builders and good listeners have the same exact goal, ......building and listening to - zero NFB triode amplification....phono preamps included. Only someone who builds using distortion measuring equipment, of maybe by oscilloscope, will endorse negative feedback, usually someone who is typically EE trained. I have found that the majority of these types of people get CREAMED, DESIGN WISE, by people who BUILD BY EAR, and only MEASURE afterwards. Actually, one should use both techniques, with the ear having the first and the final say-so.. What is the point - of having an amp that measures good, and sounds bad !!! In the END, all I seek is a good sounding two or three Watt amplifier - for my own over-100dB speakers. It doesn't matter to me how well it MEASURES, OR, if I understand it fully, and can adequately explain to others ..........why it does - what it does. No, not one iota !! So............ I suggest to all regarding " theory" - this : "Don't tell me about the Pregnancy, just show me the baby!" All this is authored in an honest way, and I am meaning to be respectful to you, and all others, as I express my personal opinion. It matters not to me, if you accept it or reject it. I believe, and that's what matters to me. Besides negative feedback, any high DCR Power supply, ALSO changes the timing of the amplifier, and its ability to resolve music, its PRAT. I hate high DCR supplies also, what a waste !! Jeffrey Medwin
  8. Very simple to understand, and very audible. Important also ! If you feed a small portion of the signal that has gone through the amp stages, (and is at the Finals stage ), back to the new, incoming Input stage signal, and combine them in any way, you are now amplifying both signals, the new and part of the old. Sadly, the new ( pure ) Input signal is now polluted, with a portion of a now-time-delayed Output signal. Decent circuit designers strive to use as low an amount of feedback as possible. Why? Because the amplifier plays and sounds more natural, and " in time "/ more pure. Like real music !! . Personally, ......... I suggest using no feedback in amplifiers - at all. The " circular babble " words you used are perfect, not regarding my response herein, but it aptly describes what happens - in any amp circuit with feedback !! Triode stages, well designed, often can use zero feedback. The benefit is most easily noticeable, laid bare, on our highest efficiency speakers, which do easily differentiate this to their listeners . 100dB speakers, and higher. Jeffrey Medwin
  9. Greg, It might be a LOT of fun, and it can produce much satisfaction, if a DIY build, ( with your friend's actual assembly - soldering help ) was done. There is great satisfaction when its " yer Baby" VS paying someone for a finished product !!! We would have time to settle on a design for you, between now and MAY, or find a good USA No Neagtive Feedback Push Pull amp. I would ONLY like it to be two stages ( KISS ) and if possible, eliminate the Coupling Cap, by Direct Coupling the two. Transformer coupling is second best, a capacitor for coupling is the least best, generally speaking. Been working ALL WEEK on designing a Phono Preamp - Power Supply that I'd really like to build. Many many hours, PSUD simulations up the wazoo !!! Its getting there !! Jeff
  10. I am thinking of a Japanese parallel here. In the case of Isamu Asano, who developed a SE DC 2A3 amp, of Japanese acclaim, his son Tadashi took over the design upon Isamu's demise, maybe around 2006. Tadashi did two things I detest, to his Dad's circuit !! For one, he added a negative feedback loop to the SE 2A3 amp, so it plays out of time to the music !!! Secondly, an other questionable change was to add hum pots, to the 2A3 filaments. He interjected a diode effect, between the pot and the wiper's contact, to the critical signal path of the 2A3 cathode's return to ground................... without engineering it properly. Wolfbane, I feel you are barking up the wrong tree, looking for older Shindo gear. It will not be that high in audio performance !!! There are people in the USA who build good stuff. You probably should look for a 8 to 12 watt Push Pull amp, with NO NEGATIVE FEEDBACK, and a great low DCR power supply, if you run traditional vintage Corner Horns. The vintage Klipsch speaker, with a three way crossover, and inefficient wiring, excludes the optimal use of the very best SE amps, ( which would typically be with 2A3 outputs, 2 to 3 Watts or so, that we have discussed. ) The best SE amps need to be used with a highly efficient speaker that is ideally at most, a two way speaker. I run a two way speaker at my home, and I won't use any crossover at all, on the 15 inch horn-loaded woofer. Just a roll-off on a compression tweeter driver. ( 515B, 802D, A7-8 ). Sometimes, less is more !! Surely, someone makes a decent no feedback low power Push Pull amp in the USA , with a good supply. Not 6BQ5 amps, but Push Pull 6CK4s, 6AH4s, 6AQ5s, or 2A3s could be made to really PERFORM and run rings around what is available !!! If you did DIY, I'd develop plans for you to follow !! Well, that's how I see it, my opinion. YMMV. Jeffrey Medwin JUST FOUND THIS, WILL LOOK SOME MORE. Another quick example found : https://www.diyaudio.com/forums/tubes-valves/236536-4p1l-push-pull-amp-lundahl-zero-global-feedback.html Finally: BELOW : This, is GREAT topology, only two stages, AND directly coupled, no paralleled output tubes, from 1991, could be nicely implemented and updated , use 6CK4s, in 2019.
  11. In my opinion, on most Klipsch speakers, you should not need to use a 75 WPC amp. Usually, there are better sounding tube amps, of the Push-Pull variety, in the 12 to 20 Watt range, that should readily out-play those Carvers. The task is to FIND them, and give them an audition in your own system. Ask for suggestions from Forum Members, low powered Push Pull amps, hopefully with NO negative feedback loops in them. Does QuickSilver offer such an amp? Hes pretty good at design. Single ended amps are best when they are LOW in power, 1/2 Watt to 3 Watts is ideal, and up to maybe 5 Watts generally. Such SE amps require 100dB + speakers to shine. Jeff Medwin
  12. The input tube. Pin 6 is the tube's plate resistor connection, and the resistor is denoted as R16 on the schematic, 270K Ohms, or 270,000 Ohms. Closest double-the-value stocked MK8 would be 549K. Two in parallel, will become 274,500 Ohms computed. That is about a 1.6% difference in theoretical R values .......surely CLOSE enough IMHO. The original part was likely a 2% or 5% 1/2 Watt part, especially when we compare that part's lack of designation on the schematic to the complete designation of R21 and R20 - of the tube's triode-section / phase splitter, (Pins 1,9,8 ). The second-most significant R -treatment possibility, would be to do something to the four 47K phase splitter Rs ( R21, R22). Alas, no MK8s exist close enough to parallel, and the fabulous Mills from Percy ( MR-200, 200K ) are 2 inches long, and well beyond this amp's need, from what I see. I was thinking about how to meaningfully make up your $25.00 minimum order. I would appreciate it if you did JUST R16 and listened, and share it with others on this Forum. I am sure, for example, that ALL the Dennis Had budget-priced "Inspire" amps would be excellent candidates. You get to be the known-to-all guinea pig, as I am new here, and not fully understood. This is so much better, than just " tube rolling " alone. Tube rolling alone, is like adding using a lovely Rolls Royce, along with a FIAT 500. Lets have ourselves a Rolls and a Ferrari ! If you have additional Qs, you can always PM me. Jeff Medwin
  13. Hey, good post. Go the next step !! Measure and determine what the Ohmic value is of the plate resistor in your first stage. Write that down. Look in Michael Percy's 2-2018 catalog, and find the closest DOUBLE the value Roderstein MK8 ( 2 Watt ) German film resistor. Order four, for both channels. Have Mr. Percy match them into two pairs, NOT to the rated value, but to their respective measured values, to each other ( get 'em at 0.01% or closer). These Rs are only $1.95 each, and the matching is a dollar more. Carefully, neatly, replace the existing stock plate resistor ( of your INPUT TUBE ) with these matched doubled up MK-8s, and LISTEN to what that does for your music enjoyment. You use a modded ST-70. You will hear it. You see folks, when we hear any tube amp, we are not just hearing the tube, but the tube in conjunction with its plate resistor. The INPUT tube is the most sensitive spot in the whole amp. The end result, will probably be far better sonics, than tube rolling alone, which is playing cards with half a deck, my analogy !! Michael is superb to deal with, $25.00 minimum order, easy to fill with all HIS goodies. Please report back to all. Doubled up / very tightly matched MK8s are unbeatable, price VS resultant audio performance, from what I experience. Tell us ALL what you hear !! No substitutions on R s, only use MK8s please !! Jeff Medwin
  14. Interesting learning experience, last few weeks and days. A vacuum tube Passive RIAA EQ circuit, that is feed forward, ( and not using negative feedback ), typically has many thousands of Ohms of series resistances added to its plate-driven circuit. This is done by almost everyone, as " conventional EE wisdom " because the added resistance assists as tubes age, and, in primarily - getting the circuit to very closely follow the RIAA EQ. Here are some passive RIAA circuits that come to my mind, with their added series resistances : Thomas Meyer ( 6SF5-6J5) 200,000 Ohms added Original RCA phono EQ ( 12AX7-12AX7) 470,000 Ohms added Eli Duttman's modified RCA ( 12AX7-12AX7) 255,000 to 265,000 Ohms added Jeremy Epstein's ( 6C45Pi-6C45Pi) phono stage, 28,670 Ohms added. Bruce Rozenblit's ( 6C45Pi, 12AX7 ) phono stage 91,000 Ohms added. Andrae Ciuffoli ( D3A-D3A) 220,000 Ohms added. Salectric ( D3A-5687) 21,500 Ohms added Whenever you take the audio signal in a passive phono EQ, and pass it through a any such series resistor, ( as above ) you have a sonic degradation, VS a resistor not being there at all. People who design and listen, will all tell you " the less resistance in series there is, for the signal to drive through, the better the preamp sounds. " I discovered, over the last three weeks, that perhaps three high end phono Manufacturers, ( or more - perhaps some that I am unaware of ), might be using NO added series resistances at all, for the signal to pass through. They all believe an L.P. music-source, played back through such a phono stage, SOUNDS BETTER to them !! How VERY interesting. The decades-long conventional strict adherence to the RIAA curve, is possibly totally trumped by play back, sounding better, with zero series resistances used !!!! Well, as part of this thread, and as part of my tube phono preamp's design, I have decided to have NO added series resistances in my upcoming phono build. I also decided to not use the lovely 6C45Pi ( highly variable, and it can oscillate ). Rather, I'll design with the 12AX7, or one of its variants, as a more conservative possibility, including perhaps even the use of a 12BZ7. I have several really good thoughts on how to precisely implement a 12AX7, it takes extra care. B+ supplies in the new design will ( uniquely / heavily ) be double-series-shunt fed, for each B+ use-point. If the entire audio circuit draws 70 milliamperes, this planned double-series-shunted supply may draw an additional 110 milliampreres, so it becomes a 180 milliampere Phono stage ..... like a small power amp, will be the current requirement. Two tube rectifiers, not one, and three series B+ chokes, all three chokes, each under 7 Ohms in DCR. Henry Pasternak's "Flywheel" input filter. 15 Ohms total - for all three, is the series choke DCR. Phono preamp will use a 10 AWG m22759/11 Mil Spec ( stranded copper-silver plated ) ground buss . Am PSUD-optimizing this supply, doing many iterations of simulations these days. Truly much work, but fun stuff. ADDED 11-26-2019 : No wheres in audio, has anyone ever built a supply with the topology as seen above. Most people seriously underestimate the need for a truly great preamp ( and amp ) power supply. Ever see a phono stage that starts with a 525 mA. Power Transformer, dual directly-heated tube rectifiers, and uses a below 1 Ohm low DCR Input choke ?? And has a separated brute force double-series-shunted B+....... for each and every triode section? What is this design going to sound like??? I think I know already, from my 2019 KT88 DC amp build, which I had designed to be double-shunted, ( for the amp's Input/Driver stage B+. ) This new phono preamp, funds permitting, is to be built and its performance determined - hopefully in 2020. Jeffrey Medwin
  15. Did everyone notice the Specimen web site ? Refreshingly honest : Terms : 50% deposit, non refundable. Delivery : 6 months to 2 years.
  16. Nice looking 2A3 amp. I've been working with SE 2A3 amps powering efficient speakers for the last 13 years, and with wire for audio for the last 41 years. My best conservative no-risk advice in 2019 is to use three parallel runs of Mil Spec cable, specifically, M22759/11, for each amp-speaker polarity. Two of the three should be 12 AWG, and the third 14 AWG. Minimum lengths should be precisely 9.52 feet, which is 57.125 inches times two. If you need longer cables than that, go to some multiple of 57.125 inches, usually times three ( 14.28 feet ) will do. Keep the descriptive lettering, on the wire's outside, going in the same direction, for all three wires in any trio. Connect them, descriptive lettering - amp to speaker, uniformly also. Terminate both ends into spade lugs sold by Michael Percy, budget priced gold plated and, I believe, capable of accepting 8 AWG wire. Use a Weller D-650 or D-550 - 300 Watt or 325 Watt soldering gun, to solder the spades and wire. Do not allow the two wire polarities to touch each other, on its way from the amplifier to the speaker terminals, nor touch the floor's carpeting, etc. This above, will insure the best possible linear and wide-band transfer efficiency, 2A3 amps to speakers, on a cost versus performance basis. Look up what M22759/11 wire is !! It is multi-stranded copper , with each copper strand silver plated, in a teflon outer jacket. The silver content is important ! Readily available, surplus and Steve at Apex Jr, on line, is a trouble-free great source. If you have any additional questions, feel free to ask. Happy Listening. " An inch of bad wire can ruin the musical experience ". Its wonderful that you inquire - on how to do it optimally. Nothing is perfect, but this is easily the best "I" am aware of in 2019, and what I use. Jeffrey Medwin
  17. Nice post Maynard !! I'd like to add, always remember this folks : the transfer efficiency of the wire used, between the amp and all-the-way to the drivers' voice coils, is also a factor in how much amplifier power is needed. Irrespective of the speaker's " dB " at-one-watt rating . Jeff
  18. Something new : 'Am thinking of doing a phono stage using Russian 6C45Pi tubes, and a 12B4A Finals stage, in lieu of 12AX7s for the EQ. Any of you tube listeners have experience with the 6C45pI? How does it strike you ? Comments welcomed. ( Bruce Rosenblit's Phono stage uses a 6C45Pi in the first stage, and a 12AX7 in the second ). I've never heard it. Have you ?? I think, use of a 6C45Pi in both EQ stages, is commercially unavailable, and limited to a DIY build effort, I am talking to Jeremy presently. http://home.earthlink.net/~jeremyepstein/6c45riaa.html IF I do this, I designed a brute-force power supply, tube rectified, ' got it all PSUD simulated - for it. Jeff Medwin
  19. Thats easy. When both choices ( anode-drive, cathode-drive ) are properly executed, and generally speaking, a cathode follower does not sound quite as good - as the music's signal being anode-driven. In more familiar-to-audiophiles' terms : this is perhaps why some prefer the sonics of a simple, modest two tube DYNA PAS-3 RIAA EQ, when it is well modified, over the three tube ARC SP3A-1 RIAA EQ, having a cathode follower. In my home system, I purposely use no line stage preamp, to avoid the extra circuitry. I just have a DIY 10K System Attenuator, Ladder type, with source-switching ( selection ) , to feed my SE amp(s). A solid state Blu-Ray player (Pioneer Elite BDP-09FD ) in use, can easily drive 10K. But a tube RIAA stage, normally can not. Jim Dowdy ( " The Dowdy Lama " ) came up with the idea this year of using a high current triode, to DRIVE 10K from the anode, to avoid a cathode follower. This takes over 33 mA. of idle current, a whopping amount - to do this !! So, I eliminated the Coronet's 12AU7 Cathode Follower third stage. I figured out how to directly couple the 12B4A to the preceding two Coronet RIAA EQ stages. The direct couple, avoids a cap in the circuit path, between the two stages. Good !! Its hilarious in a way, the stock Coronet's four 12AX7 RIAA EQ sections draw 3/4s of a mA. each, ( right " on the money " ) or 3 mA. total, but the two 12B4A tubes will use a total current draw of 66.66 mA, ....to drive 10K from the plate. The 12B4A triode is a linear tube, decent sounding. Jeff Medwin 12B4A.pdf ------------------------------------------Click on this to see the interesting G.E. datasheet on a 12B4A. Next is a comment "The Dowdy Lama" just made to me in a email this morning, on 11-7, re Cathode Follower avoidance :
  20. What are your thoughts of it? How does it compare to other tube phono stages ? I have been thinking of using the 12AX7 stages' circuit, my power supply, and adding an anode-driven 12B4 output stage, instead of Jim Hagerman's Cathode Follower. Jeff
  21. These Mono 60s, have two NICE advantages : besides being MONOBLOCKS, they also use DUAL 5U4GB rectifiers. Because of this , a pair of 60s out-performs the other McIntosh amps of this era, I've been told, and in particular, all McIntosh 275s of that era . If you need power, this should be long-term-excellent to own. 'Just my understanding , just expressing an opinion, subjective and technical reasons stated.
  22. Yes, I think the O'Netics are worth their original price, today, as are any Magnequest MQ DS-025s or MQ ES -025s.
  23. Wolfbane, Your referenced article deals with DC heating of tube filaments, typically done with DHTs ( directly heated triodes ). I TRY to totally avoid DHT Finals ( output ) tubes that require DC heating, because AC heating sounds better to me. This means, in DHT tube amps, use of a lower voltage rated AC filament - 2.5 V-rated filament Finals tubes, rather than use of 5 V-rated (or higher ) filament Finals tubes. This means starting a DHT design with a 2A3 as the Finals tube choice, or maybe a 45 if you like them, not a 300B, or a 6B4G, etc etc. This above, is not a concern with INdirectly heated 6.3 VAC Finals tubes ( 6BQ5, 6AQ5, KT88, etc. ) The 2A3 DHT's lower rated voltage, applied to the filament, allows one to get away with AC heating, on 100+ dB speakers, with very acceptable hum levels. AC heating ( VS: DC ) of a 2A3 amp will sound better to most experienced builders, who experiment with good equipment, sources, speakers, wire, etc. For a tube power amplifier's front end tubes, typically indirectly heated, most will use AC heating. - - - - - - - - - - - - - - -- - - - - In 2019, I have changed my designs to use totally separate Filament Transformers, for the front end - and ALSO for the rectifier tube's filament supply. When you use a single power transformer in a power amp, that is doing duty for the High Voltage B+ / Plate supply to the Finals. This INTERMODULATES all the amp's other powered filament supplies. The intermodulation, or "buckling" on transients, of PULSED musical information is very audible to me. This occurs, even when the front end tubes are (usually) INDIRECTLY heated ( have a cathode). Amazingly to me, we hear the filament's intermodulation "through" the cathode. Tube preamps have different filament heating requirements ! Of course. Lower signal levels prevail. People have found, the use of a separate Filament transformer for amplifier's rectifier tube ( only ) always plays music better, more dynamic , more FUN to hear - than if it was powered by the same Transformer that powers the B+/Plates of the Finals. The rectifier is the first tube that demands a separate Filament Transformer, IMHO. Hammond makes em, 3 A. rated ( 167M5 ) and 6 A. rated ( 167Q5 ). Small, reasonably priced. Next in line for a " separate" treatment is the Input/ Front end, the very FIRST tube in the circuit. Hammond again - for those Filament Transformers. - - - - - - - - - - - - - - - - - Another important design pointer: It is VERY important, when ever one adds separate transformers to an amp, that ALL leads, on the transformers' Primaries, and the Secondaries be PHASE ALIGNED, to each other,........ and uniformly connected to the tube socket positions, and...... also, channel to channel. Very important !! A dual trace scope and two probes is the simplest way to commence, and determine relative phases. All these things discussed are audible, to me, and to others. In my opinion, separating the two Filament Transformers from each other, and both from the main B+/ Plate Transformer, produces the difference between any good tube amp...... and a great tube amp !! Jeffrey Medwin
  24. This belongs to a friend of mine, and I have it listed for him. Its got a week to go, on eBay, and its only at a dollar bid as I type this !!! Very high quality pair, simply read the ad and do some research. https://www.ebay.com/itm/293289849327 Thanks for looking. Jeff Medwin
  25. The highly revered Malantz Model Nine monoblock !! Here is an interesting and true tidbit on its design. In the 1980s, I had befriended an avid audiophile, who was also the DEAN of E.E. at the University of Alabama His name was Charles A. Halijak, PhD. During his career, he published 20 papers at the University, and received 27 different Citations ( not for speeding, gents !! ). His published paper record can be seen on-line here : https://www.researchgate.net/scientific-contributions/2017834553_Charles_A_Halijak Here is what I want to tell you all. Dr. Halijak's worst-liked amplifier, from a E.E. design point of view, was the Marantz Number Nine. He felt it had so many design errors, that yearly he would have the students in his class, critique the design, and offer improvements to submit to Dr. Halijak. This was his own requirement, before they would be able to pass his E.E. course !!!!!! If any E.E. schooled by Dr. Halijak at the University of Alabama in the 1980s is reading this, I would enjoy your confirmation, of what I am reporting herein, and believe to be true. Dr. Halijak was also a big believer of low as possible / practical DCR ( Direct Current Resistance ) power supplies. I wrote about that on page 8 of a KT88 build thread, earlier this year. His favorite value power supply choke, for his own personal tube amp builds, had to be custom made back then. He had Stancor build for him to his spec : 1 HY at 8 Ohm DCR power supply chokes. Isn't that interesting, because it does not necessarily meet critical inductance, as is always taught the last maybe 100 years in all the conventional EE courses. Dr. Halijak was brilliant, look at his papers. Today, Hammond has a off-the-shelf 159ZA choke, six ohms, and it requires 75 hours of music - playing to break in. One would always use at least two of these, in each tube amp's supply, as a L1/C1/L2/C2 B+ filter to feed the Finals. Two 159ZAs, connected in series, is only 12 Ohms total DCR feeding the Finals tube, from inductors . Jeffrey Medwin
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