Perhaps I should just stay with the Mk1 and be prepared to fix it when it breaks down.When was the last time you totally retubed the VT100 amp? Specifically the 6922 signal tubes? It’s not for the novice and can be quite expensive. The 6922 input and driver tubes must be biased. Especially the driver tubes.
Next thing to consider is the age of the amp. 21, 22, years old? The power supply electrolytic caps may need to be replaced.
It may cost more to retube the amp than it’s worth. Add new caps it will definitely drive up the cost more than the amp is worth.
VT100 Mk3
http://www.arcdb.ws/VT100/VT100.htmlInternally, the circuitry of the VT100MKIII is derived from the VTM200. Like its more powerful sibling, the MKIII’s input stage utilizes direct-coupled JFETS for ultra low noise, and is followed by a 6H30 driver/gain stage, capacitor coupled to a 6H30 follower, driving two matched pairs of 6550C output tubes per channel. The conservative 6H30 driver-follower circuit will help prolong the life of the 6550Cs, and the 6H30 is rated to handle higher currents than the previously used 6922, so it has lots of safety margin for even better reliability. (The 6H30 twin triode is a Russian military tube in current production, with an estimated service life of up to 10,000 hours.) There are now four internal bias adjustments-up from the previous two- to allow more accurate DC balance adjustments for the output tubes. The line fuse has been increased to a 7 amp in 120V units (6.3 amp in high voltage units), allowing the MKIII to handle musical dynamics with greater ease.
Simply put, the VT100MKIII is a major sonic advance. As the original VT100 was greatly improved upon by the MKII, the MKIII eclipses it again by the same margin. Resolution and dynamics are startlingly better: suddenly you can pick out each individual voice in a choir, you can hear the air gently modulated by a hundred diaphragms singing in unison in a great cathedral. Small and large details stand out in bolder relief, tightly focused, wonderfully holographic. Bass is tighter and more dynamic. It sounds as though the power has been increased, with a more effortless quality. The MKIII is easily recognized as having been borne of the VTM200. Lastly, the single-ended RCA input is almost indistinguishable sonically from the balanced-XLR input.
The signal tubes of VT100 Mklll do not require biasing when retubing them like the VT100 Mk 1 and 2 do.
Complete retube of the VT100 Mk 1 and 2.
http://www.audioresearch.com/ContentsFiles/VT100_BiasAdjust_Schem.pdf
Step by step how to bias the 6922 signal tubes.
Courtesy of Abe Collins
http://mycollins.net/audio/artube1.html.
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