Gregg357 Posted April 26, 2011 Share Posted April 26, 2011 Anyone had any experiences (building or listening) to the M-125 tube amp by Bob Latino? I'm a virgin kit builder, bought the kit, and have yet to complete the build. Just curious what the word on the street is. I'm expecting it to be and excellent performer, based on Bob's reputation with the ST-70 and ST-120. Gregg Quote Link to comment Share on other sites More sharing options...
Bob Latino Posted April 26, 2011 Share Posted April 26, 2011 The VTA M-125 125 watt monoblock kit uses a modified VTA Mark III low gain parallel push pull circuit. It sounds very similar to the VTA ST-120 but will play 3 to 4 dB louder than the 60 WPC VTA ST-120. The M-125's have a slightly wider bandwidth, a 5 dB lower residual noise level and somewhat lower gain than the ST-120. 12BH7 driver tubes are recommended to give the higher voltage swings that this amp needs for full power output. 12AU7 driver tubes will also work. Either a tube or solid state rectifier may be used in this amp. The amp can use either 6550, KT88, KT90, KT100 or the new Tung-Sol KT120 for output tubes. Like the VTA ST-70 and VTA ST-120, the M-125's have a switch that allows the amp to be operated in ultralinear mode or triode mode. Bob Latino Quote Link to comment Share on other sites More sharing options...
Guest " " Posted April 26, 2011 Share Posted April 26, 2011 Bob, this is your Mark VI class amp? Quote Link to comment Share on other sites More sharing options...
Bob Latino Posted April 27, 2011 Share Posted April 27, 2011 The Dynaco Mark VI was a 120 watt monoblock amp from the mid '70's. The only thing about the M-125 that was similar to the Mark VI was the fact that both amps used a parallel push pull output circuit with 4 output tubes. There are many differences between the two amps. 1. The M-125 can use 6550, KT88, KT90, KT100 and KT120 output tubes whereas the Dynaco Mark VI driver circuit was designed for an 8417 output tube. Dynaco mentions in the Mark VI manual that there is no substitute for the 8417 tube. 2. The driver circuit on the Mark VI used a single 7199 driver tube for both the voltage amplifier/inverter sections. This is similar to the drive circuit on the ST-70. The M-125 uses two 12BH7 tubes. The front 12BH7 is the initial voltage amplifier and the rear 12BH7 is the phase splitter/phase inverter tube. 3. The Mark VI had only 75 uF of DC power storage to power the output transformer. (25 uF before the choke and 50 uF after the choke) The M-125 has 336 uF of DC power storage for just the output transformer which is about 4 1/2 times what the Mark VI had. The M-125 also has another 167 uF for just the driver board. This is not said as an indictment of the Mark VI. Back in the mid '70's the state of tube amplifier development was such that it was difficult to get a lot of DC power storage at a reasonable price. Today's electrolytic caps are smaller in relation to how much DC storage they have and are also less expensive than what was available back then. 4. The M-125's may be operated in either ultralinear mode or triode mode at the flick of a switch. The Mark VI only operated in ultralinear mode. 5. The Mark VI had a hard wired solid state rectifier. The M-125's may use either a GZ34 tube or a solid state rectifier (Weber WZ68 recommended). The solid state rectifier plugs right into the rectifier tube socket. 6. AFAIK the Mark VI was intended to be operated with 4 output tubes only. The M-125's have "two output tube" option. If you don't need the full 125 watts per monoblock, instead of using four output tubes, you can also use just TWO output tubes - one left side tube and one right side tube. The power drops to 65 watts in ultralinear mode and 35 watts in triode mode and the amp must be rebiased. Bob Latino Quote Link to comment Share on other sites More sharing options...
Guest " " Posted April 27, 2011 Share Posted April 27, 2011 Bob, super...how is the assembly manual looking? Quote Link to comment Share on other sites More sharing options...
Bob Latino Posted April 28, 2011 Share Posted April 28, 2011 Just like the VTA ST-70 and ST-120 amp kits, the assembly manual is written for the beginner. The M-125's are even easier to assemble than the ST-70 or ST-120 amp kits. Reason > Although the chassis for the M-125 (10 X 12 inches) is about the same size as the ST-70/ST-120 amp kits (9 1/2 X 13 inches), there is only the wiring for ONE channel. There are no cramped spaces or tight spots. You just do the step and check what you did against the full color pictorial photograph (smaller version above). If you made a wiring error, you will see it immediately .. Bob Quote Link to comment Share on other sites More sharing options...
kevinmi Posted April 30, 2011 Share Posted April 30, 2011 I bought and built the ST-120 kit from Bob a couple of years ago, and it was my first build project. The instructions were very easy to follow, and the support that Bob gives is second to none! Not to mention the amp sounds fantastic! I have tried to justify buying the new monoblock amps from Bob, but I don't even use all the power the ST-120 puts out. Let us know how it sounds when you complete it and take plenty of pics of the build! -Kevin Quote Link to comment Share on other sites More sharing options...
Gregg357 Posted May 4, 2011 Author Share Posted May 4, 2011 I didn't have the awareness to chronicle this build from A to Z. But here are some grainy shots from my dirty lensed cellphone, in no particular order. Quote Link to comment Share on other sites More sharing options...
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Gregg357 Posted May 4, 2011 Author Share Posted May 4, 2011 9 - Bob Latino Stock Photo Quote Link to comment Share on other sites More sharing options...
Guest " " Posted May 4, 2011 Share Posted May 4, 2011 the powder coating looks great Quote Link to comment Share on other sites More sharing options...
Fjd Posted May 10, 2011 Share Posted May 10, 2011 Nice looking project. Are the amplifiers complete yet? If so, any thoughts on the sound? Quote Link to comment Share on other sites More sharing options...
bcinnamon Posted June 20, 2011 Share Posted June 20, 2011 I just completed my pair of M-125 amps. I figured that even if my project worked OK it would sound better to me than anything else I could buy. But I was blown away; I felt like that guy in the Memorex ad. Ive been listening continuously to my collection of Jazz and rock especially tracks with sax, trumpets and guitar. Even when I crank it up to 11 the sound remains pure. My teenage kids definitely preferred the tube amp sound -- and that is from the mp3-earbud crowd! Imaging is uncanny, the tone reminds me of a perfectly tuned bell, and I hear every nuance of brush strokes and guitar slides and audience coughs in the background (apologies to Keith Jarret in advance). The saxophone on Jungleland is especially haunting tonight ;( Quote Link to comment Share on other sites More sharing options...
Cornman Posted June 23, 2011 Share Posted June 23, 2011 Welcome to the forum bcinnamon, & thanks for your review of the M-125. Please tells us what other amps you have used to compare with the M-125 & what speakers are you using. Cornman Quote Link to comment Share on other sites More sharing options...
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