Pre-Ernie Ball Music Man Amps

Can you tell me if there are any authorized service centers that will still work on the old Music Man amplifiers?

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.

Music Man HD-130. Chassis number 2475-130. It did not come with the Reverb/Vibrato RCA foot switch.

I'm looking for some MJE1692 transistors for a MusicMan RD-50 guitar amp and they seem to be very hard to find. Do you still have any of these? If not, do you have any suggestions for me?

Chassis number 2475-130, Music Man HD-130. The Vibrato Channel is getting weak and I believe it is the power tube going bad.

Can you tell me if my HD 130 amp needs a bias adjustment when the power tubes (EL34's) are replaced? I looked inside and I do see two blue dials on the pre amp board, but those are the only things that looked adjustable to me.

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