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This is a 125 watt monoblock amp IN KIT FORM that uses four output tubes in a parallel push pull output circuit. The amp is built on a 10 inch by 12 inch 16 gauge brushed stainless steel chassis and uses a modified VTA Mark III driver circuit. The recommended tube complement is 4 X 6650 output tubes, 2 X 12AU7. A Weber WZ68 or equivilent is now included in the amplifier price. Any of these tubes can be used . . . 6550, KT88, KT90, KT100 or KT120. 12BH7 can be substituted for 12AU7. NOTE - A tube set is not included with this amp KIT. On the front face is an on/off switch and three bias test pins. One test pin is used in biasing the two left output tubes and one test pin is used in biasing the two right output tubes. The bottom center test pin is a ground pin. The rear face contains one RCA input jack, a fuse holder, an IEC AC connector, and a pair of output binding posts. The output binding posts may be set up for 4, 8 or 16 ohm speakers. The amp has a switch which allows operation in pentode/ultralinear mode (125 watts) or triode mode (65 watts). The triode/ultralinear switch may be used while the amp is running. Note - Pricing $1860 for a PAIR, not including tubes. Taking deposits now for November shipments. See below. You will need a PAIR of M-125 monoblock amps for a two channel stereo system. PA -125M power transformer 4.50" W X 3.75" D X 3.875" H Weight 13.5 pounds 415-0-415 secondaries @ 450 milliamps Two 6.3 VAC @ 5 amp heater lines One 5 VAC @ 5 amp rectifier line One 55 VAC bias line A-125M output transformer 4.625" H X 3.875" W X 4.25" D Weight 11.5 pounds Primary impedance 2200 ohms Secondary impedance 4, 8 and 16 ohms List of parts. 1 - 16 gauge heavy duty brushed stainless steel chassis 1 - VTA driver board and parts set with upgraded power supply and Russian PIO main coupling caps included 1 - PA-125M power transformer 1 - A-125M output transformer 5 - Celanex octal tube sockets 4 - ground lugs 1 - 550 volt rated quad cap 2 - C24-X chokes 1 - SCM (supplementary cap module) 1 - set of ESL bypass capacitors 1 - fuse post and 5 amp fuse 1 - 15 amp rated SPST on/off switch 1 - 15 amp rated DPDT triode/ultralinear switch 3 - bias test pins 1 - Bulgin IEC connector 1 - 14 gauge 15 amp rated 6 foot IEC AC power cord 1 - 3 lug terminal strip 1 - 2 lug terminal strip 2 - 10 ohm 5 watt bias resistors 4 - 1000 ohm 1 watt resistors 4 - 100 ohm 1 watt resistors 1 - 20 foot coil of 20 gauge tinned solid core copper wire 1 - gold plated RCA input connector 1 - pair of gold plated output binding posts 1 - amp hardware set with all stainless steel screws NOTE - The amp may also be operated with just TWO OUTPUT TUBES - one left side output tube and one right side output tube. The amp just needs to be rebiased when switching to two output tube mode. With just two output tubes, the amp will have about 65 watts available in pentode ultralinear mode and about 35 watts in triode mode. Specifications for the VTA M-125 amp KIT ... Power output (4 X KT88) 125 watts from 17 Hz to 32 KHz at less than 1% THD in ultralinear - 65 watts in triode Power output (2 X KT88) 65 watts from 17 Hz to 34 KHz at less than 1% THD in ultralinear - 35 watts in triode IMD .................................. < .38% (19 Khz and 20 Khz) at rated power Frequency response ....... 10 Hz to 35 KHz +/- .1 dB at 1 watt Power bandwidth ............ 17 Hz to 37 KHz +/- .3 dB at 125 watts Sensitivity ....................... 1 volt in for 125 watts out Feedback .........................10 dB Damping factor ................14 Input impedance .............. 270,000 ohms Hum and noise ................ > 95 dB below 125 watt output The M-125 does not invert phase Dimensions - 10.0" wide X 12.0" deep X 7.10" high Weight (each) - 34 pounds > shipping weight 38 pounds
|pair of M-125 KITs with NO TUBES
$1860 + shipping
|WIRED PAIR OF M-125 amps with NO TUBES
$2700 + shipping
TUBE SETS - you can buy your tubes from any vendor you want. Jim McShane is our recommended vendor, this link will make payment direct to McShane Tubes
for four Sovtek 6550WE tubes and two Tungsol 6189/12AU7,
both types highly recommended by Jim over similar tubes
$200 total for EACH amp.
CLICK on the "add to cart" button TWICE
for a PAIR of M125 tube sets
|to place a deposit to HOLD your place in line for the M125 amps available in November, click on the button below
( $200 hold deposit )
2. How does the VTA M-125 compare in sound quality to your other two kits - the ST-70 and ST-120?
The M-125 uses the same basic circuit as the ST-70 and ST-120 and sounds very similar to my other amp kits at lower volume levels.
The M-125 will, however, play about 3 dB louder than the ST-120 and about 6 dB louder than the ST-70.
Slight differences are that the M-125 has a somewhat wider bandwidth and a little less gain.
3. What is this 4 output tube or 2 output tube option?
The circuit is arranged so that the amp may be operated with either two left side and two right side output tubes OR just one left side and one right side output tube.
For two output tube operation it doesn't matter which left side tube socket or which right side tube socket is used as long as one of each are used.
The amp must be rebiased when you switch from 4 output tube operation to 2 output tube operation.
The recommended bias setting with four output tubes is 1.00 volts DC FOR EACH SIDE which provides a bias current (using a 10 ohm bias resistor)
of 50 milliamps for each of the four output tubes. For two tube operation the recommended bias setting is .500 volts DC per each side
which also provides a bias current of 50 milliamps for each of the two output tubes.
4. Could a single VTA M-125 be used as a guitar amp?
The amp has a standard RCA input and is designed to be used for home audio. The input jack could be easily modified by any kit builder to accept an electric guitar input.
5. Is the VTA M-125 as easy to assemble as your ST-70 and ST-120 amp kits ?
Actually the M-125 is even EASIER to assemble than either the ST-70 or ST-120 amp kits. The chassis is about the same size as the ST-70/ST-120
but there is only the wiring for ONE channel instead of two channels. As with the ST-70 and ST-120 amp kits, the assembly manual is written in detail for the beginner.
The color pictorial photograph included with the amp kit shows the location and termination point of every wire.
6. Are there any options for the M-125 amp kit ?
No - The amp comes with both power supply upgrade caps and Russian K40-Y PIO main coupling capacitors as standard equipment.
7. Is the VTA M-125 amp available in a 220/240 volt version for 240 volt countries and can you ship one to me in (any country with 240 volt AC line voltage)?
The M-125 amps in kit or wired form are now available in 220/240 volt. We normally have the 220/240 volt transformers in stock. Email me for more details
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