Bob Latino

Just a short note here ... For those that do acquire a piece of Dynaco solid state or tube gear and would like to work on them, tubes4hifi.com has nearly all the original Dynaco assembly manuals online FREE for the downloading. See links below. Dynaco solid state manuals > http://www.tubes4hifi.com/dynaSS.htm Dynaco tube manuals > http://www.tubes4hifi.com/downloads.htm Bob Latino

Hi Jeff, Nice work ... If you follow the assembly instructions the amp should come up with no issues as your amp did. You are correct in that it will take 100 to 200 hours of play time for the amp to completely break in. Once broken in, the amp will smooth out and have a more liquid sound. I have heard this effect many times on a number of new amps that I have personally built. I am not exactly sure what happens during this break in period but it is probably something on the "molecular level". Some doubters have said to me that this break in factor is just your ears getting used to the sound of the new piece of audio gear. Personally, I don't agree with them. Maybe one day someone with the proper test gear can find out exactly what happens? Maybe do a before and after electron microscope photos of the inside of a capacitor or resistor? I had someone mention to me that he thought that the "slew rate" (voltage change per microsecond) of the amp gets faster as the parts break in? (voltage changes can occur in a shorter time period) I honestly don't know why amps smooth out after 100 to 200 hours - but my ears tell me that they do ... Bob Latino

To Fini > I am not in the witness protection program. I am alive and well in Massachusetts. In Massachusetts there are many of my family members with the (Italian) "Latino" surname ... Both the VTA ST-70 and VTA ST-120 may be had with either the standard gain 12AT7 driver board or the lower gain 12AU7/12BH7 driver board. The determining factor is usually the efficiency of your speakers. The standard gain board works well with speakers of 93 dB or lower. Above 93 dB I recommend the lower gain version of the driver circuit. Since all Klipsch speakers are fairly high efficiency speakers, the lower gain version is probably the best choice with Klipsch speakers. Another approach to deal with extra gain, is to use either the VTA ST-70 or VTA ST-120 with the stepped attenuator option. Most audiophiles use the VTA stepped attenuator kit as a volume control with a single high level input (CD player, FM tuner, mp3 player etc.) but you can also use the attenuator as a "master gain control" WITH a preamp. If you set the attenuator at about 12 o'clock and then run a signal from your preamp into the VTA amp, it will require more preamp output for a given volume level from the amp. Bob Latino

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

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

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

Disclaimer > I sell the VTA ST-70, VTA ST-120 and VTA M-125 amp kits. KHornfan, With KHorn's which are about 105 dB efficient the VTA ST-70 would have more than enough power. The VTA ST-70, although rated at 35 WPC, will actually do 45 watts over most of the audio band without clipping. See test link below. http://www.knizefamily.net/russ/electronics/electron-tube-audio/dynakit-st70/performance/ Another thing would be to specify the lower gain version of the VTA ST-70 amp. The lower gain version of the VTA driver board works better with higher efficiency speakers like Klipschorns. There is also a link below on this forum about Klipsch Grand Cinema speakers being used with a VTA ST-120. http://forums.klipsch.com/forums/t/107114.aspx Bob Latino

Above is what the inside of David's amp looked like when it got to me. One coupling capacitor had popped out completely, another was just hanging on by one connection and the other two were loose. I checked on the history of this amp and it was built with the stock coupling capacitors. The customer (who was I believe the second owner of the amp) later requested a set of Russian PIO capacitors from me and installed them himself. Unfortunately he didn't do a very good soldering job. Most of the capacitor connections appear to be cold solder connections without enough heat applied. I believe this was the problem with David's amp. Each one of those Russian PIO caps looks at +275 VDC on the inside terminal and about -55 (negative 55) VDC on the outside connection. This is a voltage swing of about 350 volts. I can't be sure but possibly after the board heated up, one (or a number of) solder connections went in and out of contact causing a 350 volt voltage spike which could take out the rectifier and/or an output tube. Just to be safe I put in a matched set of four new Russian PIO caps. The last Email that I got from you David was that the amp had been running fine since it was returned to you. Bob Latino