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Jeffrey D. Medwin

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Everything posted by Jeffrey D. Medwin

  1. When replacing the QUAD CAN with a new one, I would suggest making the FIRST section only 20 uF ( as seen by the rectifier tube ) , and not 40 uF. as shown stock. Wire it as : 6X4 / 20 uF / 1000 Ohms / 40 uf - to FINALS / etc. etc, ..................and not vice versa uF amount wise. I don't think filtering will be substantially effected, either way, ....... but it should be somewhat easier, more conservative, on the 6X4 rectifier tube. Maynard, or Backfire, what do you gentlemen think?? Jeff
  2. 06-06-2020 PROGRESS PHOTO Added six 50 Watt chassis - mount ARCOL HS series power resistors today, 06-06, mainly as part of this preamp's double - series - shunted B+ circuit. ( ARCOL is a British power resistor manufacturer, recently acquired by Ohmite. ) This involved positioning these six newest parts in the chassis, drilling holes, and hand-tapping carefully ( its tedious work " by feel " so as not to break the 6-32 tap ). All this, to be able to bolt resistors solidly to the chassis. Thermal heat-conductive paste is used between each resistor and chassis. The seven resistors you view below are continuously dissipating 50.67 Watts into the chassis, which IS well heat sinked on top. Brute force passive filtering of the B+. There will be eight more shunt power resistors in addition to these we now see.
  3. It depends upon what you mean by the preamp tubes. Some high efficiency systems today use no preamp, just a ATTENUATOR ( a passive, attenuator, either magnetic or resisitive - ie, / eg : a Slagle Autoformer, or a resistive ladder attenuator ). This passive device will also often have source switching capabilities. In this case, there are no active devices, no preamp tubes . The 2 VAC signal from a CD player, or an active Phono Preamp, gets ATTENUATED to something the amp and speakers can use, to our listening level tastes. In a power amp sir, your line of thought and question applies............ in spades. The input tube of a amplifier has THE most effect of any stage, upon the entire amp. It is a misnomer for people to say' " I have a Type 45, a 6AQ5, a 2A3 or a KT88 amp ". Look at the respective / approximate gains of those Final stages .............................which may be 4, 12, 4 and 10 times ( depending upon how used ). Question : ... What does the amp need, amplification-wise, to DRIVE those output tubes? Answer : ........... a lot higher gain . Now, if the above output tubes were used in a two -stage amp, the AVERAGE gain needed to drive these output tubes will be 50 times ( 20 to 100 times is the range ) ...... versus the Finals tube stage with a gain of 4 to 12 times, lets say an average gain of 8 times. Fifty times to eight times. The amp's front end tube has about 6.25 times the effect, upon what you ultimately hear !! 6.25 to 1. So yes, what preceeds the Finals tube stage has a SIGNIFICANT effect, on any amp's overall performance. I have often written on this Forum " If you lose or alter the music signal in ANY way in the Input tube stage, it NEVER EVER gets to be " made up " in the Final tube stage." In a two stage Single Ended audio amp, I am AMAZED at the degree of fidelity the Driver tube is capable of producing, IF executed ideally. I used the term "ideally". What IS ideal????? Here is what I have found in my DIYing : *** Ideally is having really GOOD resistors on the plate and cathode, ...HIGHLY audible. *** Ideal is having short wiring, with silver content. *** Ideal is having the MOST pristine B+ feed possible, to the tube's anode or plate resistor. Then, ( and ONLY then ), do you get to hear what is possible with a tube amplifiers. Unfortunately, 99.9% of the tube amps in existence are highly compromised in one or more, typically ALL of these above mentioned areas. They all FLUNK out. in comprehensively executing these critical areas. And tube amp owners don't even know this, nor do they like to be told this. They enjoy listening to their tube amps, which ( IME, IMHO ) are NOT really honest - to - the - music amps, but I would prefer to call them Vacuum Tube Tuners. I write all this above rather boldly, because in 2019 I designed ( with a mentor's help ) and DIY built a Direct Coupled Single Ended KT88 amp that PROVES all I have written here. And about eleven months ago, in Montana, four of us each heard this, to be totally true. The proof of the pudding. Yes, the FRONT END tube is critical in a good amp !! It is at least five or six times more important, due to its gain structure factor, relative to the amp's output tube !! Jeff Medwin
  4. 6-4-2020 ..... PROGRESS PHOTOS Started to decide parts layout for the beginning of the Power Supply. Wired in the dual 5AR4 tube sockets, careful to have EQUAL wire lengths. Positioned and drilled holes for L1/L2/and L3, and a 100 Watt SHUNT resistor ( to correct waveform of the power supply, early -on. ) I ordered several hundred flat brass washers today, in three stepped Outer Diameters, , and brass 6-32nd bolts. All the magnetics will be mounted on 6 -washer thick "brass pyramids" to the 14 gauge steel chassis for (1) magnetic reduction of fields into the chassis, and for (2) reduction of vibrations into the chassis. Today's mounting is just a test fitting. MUCH more to decide upon, on where to position and mount other parts. L1 is under 1 Ohm DCR. Swell !!. L2 is 5.12 Ohm in DCR and about 1.5 HY, - custom made about perhaps a dozen years ago. L3 is similar to L2. Detail photo on dual GZ34 / 5AR4 rectifier implementation. please note EQUAL wire lengths !!! Much more to position and do. Jeff Medwin
  5. Sorry, second attempt aborted . NOTE, equal wire path lengths to plates and filaments of these dual GZ34 rectifiers. 6-04-2020 Jeff Medwin
  6. Hello All, I want to thank Backfire and Maynard, for their contributions today to this thread. That was very nice, and apropos. I PMed the original poster, the first day of this thread, and I told him " I have large gaps in my E.E. understanding, of Negative Feedback, and of Bass and Treble controls", because in 40+ years of DIY amp building, I have never used either. There was no need for me to learn it. We DID agree, and I told him, " Within two days, we will hopefully have contributions to this thread, that will resolve the areas wherein I am deficient in my understanding." Backfire and Maynard, rather nicely, resolved those deficiencies of mine with their posts today. Thanks .......for so kindly contributing. Maynard, you realize, my lack of NFB knowledge led me to compare my ZERO NFB 2019 KT88 build, with this VoM1450, having feedback in it, which reduces gain. I did NOT get that. LOL. Its OK. And Backfire clarified the Tone Controls and RIAA EQ, questions I had, as did you Maynard today, very nicely. I do know how to eliminate the veiling, and get the unit to play substantially above stock. Its not particularly expensive to do. Several things, however, have to be done, not just one change. Why? More than one thing needs " help ", and together, all these "needing help" areas contribute to the veiling and can easily be addressed. Thanks guys, ......it is up the the O.P. now. Jeff
  7. Pete, If a 90.5dB rated speaker is your most efficient, I would say you need 5 to 15 Watts minimum. To play the low powered amp game, ( which can be built to be the best sounding tube amps ), you are best with 101 db and over. I find there is a considerable difference, between 99 db VS: 101 db and above, in general quality of playback. Of course, your room and listening source material comes into play, but I find 101 dB and above....... to be the optimal approach. YMMV, fine. Jeff
  8. Hello, I have been thinking about the Voice of Music 1450, some more. I was curious about HOW a 10 Ohm Input choke would work, so I guesstimated the stock circuit into PSUD 2 today, and compared stock VS a low DCR 10 Ohm choke amp.. Yes, with the choke I can get similar VDCs, to run the circuit. There is a deal-breaker, however, with using the ten Ohm Choke. It takes two such chokes,, and there is no room. I normally use two of them, L1/C1/l2/C2 in amps. With just one choke, the B+ wave form is not sinusoidal. So.... its a no go. There is a second concern I have been thinking about, too much gain with the second half of the 6EU7 ( mu or gain of 100 times ) driving the 6BQ5 in a pure Pentode mode. I deduce this from my 2019 KT88 SE Pentode amp build. It is using half a 12BZ7 ( similar mu - of 100 ) driving a Pentode Output tube, and it is NOT long term livable, gain-wise.. The volume pot is only operated in the bottom 5%-20% of its range, and there are other less than optimal things happening. I'm converting to a mu of 20, 6FQ7 driver tube, later this year. The first half of the 6EU7 ( a dual triode) is similar to them second, in gain. When the first half is used for all that added circuitry, Phono EQ, bass and treble controls, perhaps it cuts gain down to less than the input signal !! Whatever !! .....In any case, using the second 6EU7 triode section only will pass a signal fine, but be unlivable, long term. Two solutions : 1) Add some series resistance to the music signal, with only the highest quality resistor one can source ( Texas Instruments TF-020 as an example ). This is the EASY way to solve it, but even the best resistor, is a degrade of SOME sort !! I will NOT do that in my 2019 KT88 amp. Why here, other than ease?? 2) Find another 9 pin miniature vacuum tube, that will fit in the tube socket, and have the right characteristics. It must be linear, maybe a mu of 30 to 70, draw about 1 mA. of plate current and have a similar filament consumption as the existing 6EU7.. Pin out similarity is not a factor. Anyone have any driver tube ideas to suggest? If so, please do !! Rome was not built in a day . Thanks. Jeff
  9. Upgrading VOM 1450 for use with Owner's Cornwall IIs. Note: The 10 Ohm Choke ( Stancor C-2708 or Triad C-40X ) is just a passing idea. It reduces the DCR to the Finals stage dramatically, which is wonderful, BUT, such lowered resistance increases the operating VDC to the Finals stage an unacceptable amount. To properly employ such a low DCR choke, would require PSUD simulating the supply, to see what the VDCs to Finals stage would become, if the FIRST THING the 6X4 rectifier " saw" was this non critical low DCR / 10 Ohm choke - and not a 40 uF cap.. I would use a C-2708, not a C-40X. Hammond's 159ZB choke, at only 8 Ohms, is the third possible inductor candidate here. It takes additional information, a few simple voltage measurements, to simulate this unit's supply in PSUD,. There is also the question of " room on the chassis ". The basic goal is to minimize the 1,000 Ohms of series resistance to the Output stage, circled in red. The original design used a 5 Watt Power resistor, 1,000 Ohms, on a " cost and room " basis. The EE was likely unaware of the DCR's penalty. WOW, 1,000 Ohms to 10 Ohms is a 100-fold decrease !! Reducing series DCR to the Output stage is THE best audio design thing to do. ( See Dr. Charles A. Halijak, prior Dean of E.E., University of Alabama, , " Figure of Merit of the Power Supply ". ) Here : http://db.audioasylum.com/cgi/m.mpl...figure+of+merit+of+a+power+supply&r=&session= Jeff Medwin
  10. Hi Maynard, Two more questions please : Would the NFB loop consist of the R= 560 Ohm, R = 6,800 Ohm, C = 0.001 uf, attached to PIN 9, the cathode?? Could I eliminate the first tube section and its associated parts, and simply keep the circuitry mentioned above.??? Thanks, have a lovely day . Jeff
  11. Hi Travis, I never met or knew of Art before. Seems like an A1 great guy !!! I was a stockbroker with Prudential Securities, in their Beverly Hills office, until 1984, when I moved to Kansas City, MO. to trade the Value Line ( stock index) at the Kansas City Board of Trade. Did so, 1984-1988, and sold my KCBT seat in 1988. Could you take a minute and edit the next to last sentence of your post above.?? Thanks. Jeff
  12. Hello Art, You are posting the obvious. When I suggested TVIX, (which I can not and will no longer do ), it was on January or was it February 27th as I recall, in the mid 40s. It went to 54, 38, and then in March, went to $1,000 a share. My suggestion on my initial stock market post was VERY clear, unambiguous..........immediately go 95% into cash, and 5% into TVIX. This would have allowed someone to possibly double their money during the March 2020 decline, while being 95% in cash. You have to hold it, to get that to happen. Can you think of a better suggestion, portfolio allocation, as of January or February 27th, 2020? I certainly can not. In honest retrospect, it was possibly the single simplest, best thought-out thing to do. Jeff Medwin PS. ART: As you and I would expect, no one on the Klipsch Forum followed me then, as I had advised. Since then, I have been told, no more specific advice allowed, for legal reasons. I agree, understand, and will only occasionally express my market thoughts. I am willing to take more heat, cooly, have bigger equity draw-downs, take more risk, than an average person.
  13. Hi Maynard, I liked the power cord and fuse suggestion a lot. But how do you justify running a CD signal ( needing a flat LINE stage circuit ) through an EQed VoM Phono Input? Please tell me, what am I missing, not understanding here?? Jeff Medwin
  14. Wait a minute. You can get stereo sound with two mono integrated amplifiers ( V o Ms) !! Plug the Left channel output of your CD player into one VoM, and the Right channel CD player's output into the other VoM. Yes, you do NOT need tone controls, if you have a GOOD hi fi system !!! You do not necessarily need to buy a Line level Preamp, if you are only using a CD player as a source. It has a couple of Volts AC, output, all you need to do is turn it DOWN, no gain usually needed. You can build a Passive System Attenuator, for several hundred dollars, using QUALITY parts, that can sonically out perform MANY and maybe most of the tube preamps out there. First, you still need to resolve HOW to use these VoMs with a LINE ( CD player ) input !! If Maynard doesn't see this thread, or if Alex Kittic doesn't, reach out to either of them via a FORUM P.M. Michael Percy is Michael Percy Audio, a class act, for decades, a GREAT source for some of the best sounding parts in AUDIO. Lovely person too. Download his catalog. from 2-2018. Yes, I will try to assist...... any time you ask. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX As I look at this schematic some more,..................... I THINK you could remove the 0.005 uF series input cap's connection, from the wiper of the 1 Meg Input / Volume POT, and JUMPER a wire from the 1 MEG POT's wiper to PIN 8 , the second half of the Input tube. Carefully REMOVE the wire connected to PIN 8, before soldering in the jumper. This KEEPS the Volume control functional, but eliminates the first 1/2 of the 6EU6, with all the PHONO EQ /Bass/TREBLE control circuitry !!! How wonderful THAT would be !! You get to TOTALLY ELIMINATE many cheap and degrading stock VoM parts from the signal path. Superbly, you stop sending the incoming audio signal through TWO series coupling caps, ( before and after the first triode section ). Ugh. A film cap is one of the most degrading parts in audio, to a music signal. You get to eliminate an entirely UN-needed tube stage. Additionally, you get to eliminate ALL the parts associated with the Bass and Treble control potentiometers. Do you think you can willy-nilly thoughtlessly send a music signal through ANY stock cheap VoM potentiomer, one, or in this case, two, and not have it degraded ?? Of course not !! In my first post, the use of 25 cents each German MK3 resistors, will be a huge improvement over the stock murky, narrow-band carbon composition resistors. Do it AS I suggested please, listening yourself to each resistor change individually, and be sure you LIKE it, before modding the second unit. In its day, Audio Research Corporation used to use these same resistor types in their upscale gear. They are no longer made, but Percy has some. You must also eliminate the connection of the 6,800 Ohm resistor at PIN 9 of the second half of the triode, while retaining the 3,300 Rk resistor's connection / use there. The JUMPER wire ( from the wiper of the 1Meg POT, to PIN 8 ) MUST be high quality. I would suggest Wonder Wire, at only $1.75 a foot, from Percy. Order the wire, resistors, and POSSIBLY, some caps, all at ONE time from Percy. TALK to me, using Forum P.M., about possible cap choices !! Always with your budget in mind, .....best bang for the dollar. While you are at it, ELIMINATE that very poor unsoldered / pressure - contact - only connection between the "HOT" phono input wire and the Microphone switch. Run a short piece of Wonder Wire from the HOT center of what was the " Phono " INPUT RCA jack ( now a LINE input RCA jack ) to the TOP of the 1 MEG Volume control. Nice neat soldered connections please, unlike the stock input path, a low-fi / high-loss Microphone Jack connection !! A new Neutrik / REAN RCA jack, direct gold plating over brass, at under $3.00 is a very effective sonic upgrade here. Please someone, CONFIRM or critique my ideas. Yes, will some other tube-savvy readers please review and critique these suggestions please. We will upgrade the 0.047 coupling cap, EZ to make a couple great film cap suggestions in 0.047 uF !!!!! This could be VERY nice sounding, IF I am suggesting the best way to do it !! I need help here. Alex, Maynard, somebody??? Ohh, and do NOT butcher and remove stock parts !!! Just please do tell us if this eventually TROMPS all over your Latino tube amp !! Jeff Mr. Medwin , Louis, ......................was my Father.
  15. Well, in front of V1 ( first 1./2) is the Volume Control, and prior to V1 ( second half ), we have the unit's Bass and Treble controls, and some sort of EQ I suppose to comply with the RIAA, as I casually see it. I would gently PM Maynard, or let him post here. He is a wonderful whiz at this kinda' stuff. Does your CD player have a volume control? If not, and if you use no Preamp or Passive System Attenuator, you will need to control the Volume feed into the VoM amp. These are cute SE units, simple. I would be VERY careful, conservative about recapping, because you can easily ruin the unit's musicality, unless you are a gifted expert in how parts sound. If these were my units, I might modify ONE as follows, putting in GREATLY improved resistors in key spots, and compare amps . ( Save the old resistors , if you don't like the new ones !! ) As follows, all parts from Michael Percy: 1) Both 220K plate resistors .... Parallel two Roderstein Resista MK3s at 443K, for each 220K ( its within 2% value-wise, and stock Rs were likely 5% ). LISTEN to that first change alone !! 2) The 3,300 Ohm Rk, ..........Parallel two Roderstein Resista MK3s at 6.65K . LISTEN. 3) The 150 Ohm Rk on 6BQ5, .........Parallel two PRP 301 Ohm 1/2 Watt resistors from Percy. LISTEN. 4) The 1,000 Ohm Grid stopper on 6BQ5, ..............get RID of it ASAP. Use a 965 Ohm Roderstein Resista MK3. LISTEN. .............. LEARN !!! Assuming you can resolve your circuit changes for the Line Stage function, before making ANY R changes, listen to both units, FIRST, test their tubes, and be sure they play approximately similar. Have fun. PM me sometimes later and we can discuss caps The two 220K Ra or Plate Resistors are in DIRE need !!!!!!!!!!!!!!!!!! - to be buffered........ from interacting with each other. ALL this, IMHO. . Jeff Medwin
  16. 6-01-2020 PARTS arrived today...... more tomorrow. Waiting for the Filament Transformer, which hopefully arrives tomorrow - to power these - two at a time ( 6 Amperes continuous filament draw ). Hammond''s 157Q5. Made in Russia. Jeff
  17. Mike, I re read this thread, and want to say that your sense of neatness in wiring and general layout is nice to view !! A 716P is easily preferable, to a 715 orange drop. The 716P has copper leads, and is designed for PULSE duties, which is what music has a LOT of !! Also, I don't think there would be much difference if you subbed a 0.22 for a 0.27 as called for in the schematic. Do ASK Maynard !! A great 0.22 is the 0.22 uF DynamiCap, its one of the finest 0.22s available today. Superior to the less expensive REL RT. The only other one I'd consider in 0.22uF is a Mundorf Supreme Silver / Oil, and that is quite a bit more expensive than any we have mentioned. The Mundorf Supreme Silver / Oils misses some extreme top end. It just needs a really GOOD, well chosen 0.01 across it. The S/O is voluptuous sounding. Ferguson in Germany makes those caps for Mundorf. The 6AQ5/6005 is one of the BEST audio output tubes one can use !!! A Firecracker !!! I have built three 6005 amps, two stage, but without coupling caps, and negative feedback. ALL three DC 6005 amps rocked, the TUBE is great, better than any 6BQ5 IMHO !!! The 6SF5 is a great tube also, mu of 100, and its like a 7B4, except its Octal, not Loctal. Take it apart, its GREAT because the filament, cathode sleeve, and plate are all round and symmetrically distanced !!!!! It can sound LOVELY !!! Don Garber used the same driver tube in FI amps, and the 1947 Robin - Lippman D.C 6B4G circuit did likewise. Jeff
  18. So you wished you had bought TVIX below 50, ...........you have, I think, more than once stated. I just discussed the action in TZA, a inverse ETF, which made its all time HISTORIC low on Thursday, and closed UP for the day Thursday, on huge volume. ( A classic one-day reversal ). You posted a one day Dow Jones chart of Friday, shows a big sharp rally, on news, when Trump spoke at 3 PM, and went easy on China,. Did anyone, or everyone, or did YOU Jeff Matthews, notice............. what TZA did in that UP day, Friday ? TZA traded on Friday, and closed UP for the day, ( and its an INVERSE ETF )....................... on the biggest volume it has ever had. One of my trading group's threesome, the one I identify with the most, tells me " If the market has a 60 percent sharp correction (sharp as in taking only 30 days, not 18 months ) , TZA could possibly trade at 300 to 400 dollars a share in his opinion. It is now one trading day off of its all-time low. What I may do, or other members of my trio may discuss between us, is NOT meant to be taken as stock advise for others Jeff, when I was a stockbroker in the late 1960s, I liked to tell my clients, " Why don't we buy some PRD, Poloroid, Corp., and see what develops". Have fun, we shall all see, in the months ahead, what happens. Jeff Medwin
  19. I don't know. Depends totally upon who you find to do the work. And how it is built below deck. Maybe 2 to 3 hours, maximum labor for both sockets, hard to tell without seeing HOW its built. Jeff Medwin
  20. Its in years of practice, just using a single tube socket. I would NEVER EVER consider the use two male-female connections in series, especially with a PC board trace connecting the runs. I would rewire the socket, NEATLY, If I needed to. Jeff Medwin
  21. 5-31-2020........................................ DESIGN PROGRESS TODAY Developed a bracket attachment, of a B+ SHUNT RESISTOR, to the new BUILD MODULE, with the least amount of wasted space. It employs the male 6-32 stud, at the top of the 3 inch HEX STANDOFFS I decided to use this week, for Build Module-to-Chassis attachment. I am pleased with this, so far. "Ra" above stands for the tube's PLATE or ANODE RESISTOR. Economical mechanical design, vertical, little wasted chassis space. 50 Watt 1% Power Resistor will dissipate 4.5 Watts, and should operate, with these tiny heatsinks, trouble-free. This resistor is rated 14 Watts, with no heatsink at all. Yes, I used thermal grease. Four of these 50 Watt type of R-SHUNT assemblies are to be used, on the second and third tube stages, as final B+ SHUNTING, of a multiple series SHUNTING circuit arrangement. Fastidious attention to the B+ supply easily gives the best possible results, in terms of both dynamics and definition. Jeff Medwin
  22. Hi Dave, Am not sure about the label maker, but I am thinking of using bigger lettering, so as to have even better energy transfer efficiency. Jeff
  23. It is technically better to get someone experienced, to re wire the driver tube sockets, soldered connections, rather than adding a second set of plug-in connections. You will find there are MANY excellent 12AX7 types , and each has a different character. I suggest you permanently have someone carefully and neatly rewire the tube sockets. " Double" tube socket connections, whenever using adapters, is a trade-off between convenience and it trades off sonics...it is sonic degrade. What sort of analogy can I give, that is readily understandable - on a gut level ??? I got it ! Adapters is like a guy using two condoms. Jeff
  24. Maynard, I stand on the shoulders of my Audio mentor, Dennis Fraker who has over half a century of direct tube-design experience, and who owns Serious Stereo. Look up his web site, he KNOWS !! Dennis is THE expert in audio, on multiple bypassing. He finds, and reliably clues me in on various caps, over the last 15 years or so, employed in his present and past designs, which get applied inside this new preamp prototype. This preamp has a ( newly-designed ) anode vertical " Building Module ", for each tube. The 3 inch long HEX STANDOFF can allow me to easily unbolt the building module from the main chassis. I can remove the module, and replace a cap type ( or, more likely ADD a cap value, IF I detect a drop - out between cap values ). I am excited about having developed this vertical Building Module. It was needed !! In the 2019 build project, that KT88 amp, it became totally IMPOSSIBLE to work on this stereo amp, once all the needed bypass caps were installed. ( We drove that amp 3,400 miles to Montana and back, 7-2019, on my annual vacation from work, to get that final bypassing done by the maestro - Dennis ). I plan, in late 2020, after this preamp is working, to re-do the 2019 KT88 / KT150 DC SE amp, ......and " Building Module" convert it. The 2019 stereo amp has EIGHT cap bundles requiring building modules : for each channel's Driver Ra, both input and finals tubes' Rks, and each of the KT88 / KT150's G2 Final Filters. At the same time, I will be changing the amp's Driver tube from its present 1/2 12BZ7, to 1/2 6FQ7. Why? Because the KT88 / KT150 as I operate it ( ideally - from a SHUNTED B+ separate G2 supply ), has too much gain, VS when this same output tube is more commonly Triode or UL connected. A lot of re-work to do that amp !! This winter. Preamp build first, lotsa L.P.s a waitin '. I am hoping Maynard, that this new tube Phono / Line Premap will easily out-perform and sonically wipe out, all the top-of-the-line current and existing preamps ever available, priced at $20,000 and higher. We actually now think....... that it will ! Jeff Medwin Dennis, a Montana Trip, 7-29-2019
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