Hi,
I bought my Music Man new in 1979. I recently re-dicovered it after several years in the attic. I'm planning to re-condition - polarised caps as needed, also a kludge done by a tech - I feel I owe it to Leo to put it back the way he intended. While I'm waiting for an ESR meter to arrive I thought I would mark up some photos so I can check against the schematic. The pictures are from underneath the board, but flipped so that they match the layout of the components, and marked up with the tags from the schematic. I hope they may be useful for newbies like me. I've checked them over a couple of times, but if I made any mistakes I'm happy to update. Thanks for a great forum!
Attachment:
| Attachment | Size |
|---|---|
 GP1 preamp end | 1.67 MB |
| GP1 power amp end | 1.6 MB |
| Capacitors | 24.9 KB |
| Resistors | 24.96 KB |
Didn't have time to view the
Didn't have time to view the attachments but I would $%#&can ALL the electrolytics in the amp regardless an not even bother to ESR them. use your ESR on the signal caps and the like if you wish but just junk the rest. They are 38 years old and they DO dry out. Do them ONE section at a time and fire it up between sections to be able to isolate WHICH area is a problem is case there is an installation issue or bad cap. THEN move on to checking ESR AFTER the amp functions with new Electrolytics. Be CERTAIN to replace the Electrolytics on bias and supply board. Oh wait-don't know if RP's have separate board or not. Never worked on one. anyway, the principal still applies. Mike.
Thanks
Hi Mike, I will take your advice, thanks.
Mark tool?
Nice job on the photo markup. What software did you use the insert the symbols etc.?
If a few more members took this effort we would have a pretty cool library.,. Maybe a project for some ambitious highschool students (?) to work on. Do schools even have "olde ttyme" electronics shop classes?
Mark tool
Hi, thanks.
I imported the pics into powerpoint and overlayed the tag shapes in there. Also used flip horizontal in Mac preview.
I replaced all the electrolytic caps and the kludge. Also the resistors in the power board which I saw on another post. I soldered in the new caps from the back of the board which seemed like the right approach, the original copper traces were still robust. Finally replaced the original Silvania tubes with Hot Rox E34Ls, early breakup. The amp sounds bright and full of tone like the day I bought it. I watch a lot of amp reviews on YouTube and I've never heard another quite like it.
Thanks for a great forum, it gave me the confidence to attempt the job.
Good job for PCB drawing
Hi, i'm French user of Musicman RP112 (mine is 100w)
Good job for your PCB drawing.
they will be useful for future repairs.
Electrolitics caps replacement is very important for old amps.
However, if you can, check the SPRAGUE capacitors before changing them, they are often still in good condition despite their age.
Like kdkevindraper my PCB is GP1. For the power tube, you can use 6CA7 JJ which are a good compromise between EL34 and 6L6GC. And which are the original tubes provided.
You can change the two 100nf/100v ceramic disk cap on the AOP power rails by good Polypro Caps with same value.
And and for those looking to replace the EVM12L loudspeaker, the Swamp Thang Eminence speaker is a great compromise between weight, power, sound and tone.
Good music.
Otherwise, the 150uF on the low voltage power supply are also to change. 220uF / 63v is a good replacement.