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In Reply to: Message for Mark Gilmore-Re-review of the M60 posted by Jerry Mann on August 10, 2001 at 16:55:38:
"We went with a different power transformer, which is a slightly larger unit in the version II.2. We boosted the power-supply capacity in the output section by 50%. We added the quick-bias feature, where you have the two switches on the front panel for using the bias meter. And finally, we boosted the filter capacitance in the driver supply by 50%. What we did in the driver supply when we boosted the capacity was, basically, we made the power supply a bit more stable. We found that at high power levels we were getting a little bit of noise. The driver circuit was modulating the power supply a bit. So we stabilized the power supply and cut the noise down by an order of magnitude. The result was a measurable drop in distortion in the neighborhood of 40%. We added resistors to the output section to help the tubes work better together, and the effect of that was to reduce distortion by about 90%."Ralph's quote is provided above for reference.
In the latest version of the M-60, the drive stage power supply has two extra 100 uF caps, which are isolated from the existing pi-filter with a pair of 600 ohm resistors in each phase. These two new caps feed the input stage, while the original pi-filter output still feeds the driver stage.
The new resistors in the output stage are simply a reference to the one ohm plate resistors.
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