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Post by zpilot on Jun 23, 2016 16:09:10 GMT -7
I'm not at all familiar with the Monza. Having made that clear here is my rule of thumb regarding output tube drivers. I usually replace those every other time I replace the output tubes. If the output tubes were NOS I will will replace the driver every time since NOS tubes last much longer. Also, if the driver is an NOS 12AT7 it will probably last longer so allow for that. I think the Monza uses a 12AX7 so I would replace it along with the EL84's every time.
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Post by easyed on Jul 11, 2016 10:36:24 GMT -7
EL84's don't require as much current as larger bottles, so a 12AX7 PI will generally last twice as long as the EL84 power tubes (if all tubes are of comparable quality - all NOS or all current production.
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Post by easyed on Jul 26, 2016 15:35:51 GMT -7
Addendum to last post: It's true for a Monza (2 x EL84), but not for a MAZ 38 or other 4 x EL84 amplifiers, twice the tubes draw twice the current and I'd recommend replacing a 12AX7 PI every time you replace power tubes.
12AT7 and 12AU7 tubes have considerably more current passing capability (but less gain) and tend to survive longer as driver tubes and PI's.
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