HD 130 Filter Board Out of Spec

jordanjohnpk

Hello, I recently purchased a fully functional HD-130 amp and accompanying 4x12 cab. The person I bought it from is the third owner after the original purchaser and the purchaser’s son. I opened it up to see if the capacitors were original and check for obvious heat damage and everything in the chassis looks great, including newer electrolytic caps. I opened the doghouse to make sure those had been updated too and to my surprise the only components in there are the two original 100 MFD at 450v (pictures below). Based on everything I’m seeing for this chassis (2275-130) there should also be two 20 MFD at 450V as well as some resistors. Since it’s functioning normally I wasn’t planning on doing much in this amp besides replacing caps if they were original, but I’m wondering if anybody has ever seen this and/or if it’s a problem?

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Fri, 08/08/2025 - 15:27

Does the amp use a 12AX7 phase inverter tube?  Is there a 3H filter choke?  The components mentioned are used in the earlier versions of the amp. If there is no 12AX7, the amp uses a solid state phase inverter and the 20uFd 450V caps and 3H choke are not needed.  See the top schematic for info and compare to lower schematic. https://musicmanamps.net/sites/default/files/docs/2475-130_and_2275-130.pdf  Hope this is not too confusing.  Good luck and congratulations.  -mgriffin

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Full Name
Jordan Petersen-Kamp
Music Man Equipment
Sixty Five 112

Member for

1 year 2 months

jordanjohnpk Sat, 08/09/2025 - 21:20

Oh awesome I see that now. Thanks, that makes sense. I’ll swap the filter caps out as they are original and call it good.