I am the proud owner of a 70s Music Man HD-130, chassis # 2475-130. I'd like to replace the tubes and bias the amp myself, but I don't know much about the amp except it has 4 x EL-34s.

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It is an early version. It has a completely solid state pre amp and a Tube power amp design which has one 12AX7A used as a phase inverter / driver tube for the output section of four EL34 output tubes.

The bias is adjustable on early versions only. You can not adjust the bias on later versions.

Last modified on Monday, 28 September 2015 10:27