Music Man 100 RD

Music Man mad more amps than we thought, many schematics out there, this one has channel switching>

problem circled in red, bombed up low v pwr supply,

power caps still good, honkin big Mallory types, pictured next to a modern equiv Nichy to show how the tech has advanced,

we moved all the heat off the board with some heavier duty resistors and raised the leads up on the zeners for more heat sinking,

after getting the pwr supply back, all the chips started getting hot one by one,  pull one chip, the next one heats up, all the way down the line, replace the chips and we get signal off pin 1 but nothing reaching the power tubes?

dang multiplex chips used for ch switching are bad,  not a problem, just order new ones, right?

wrong.  nobody has those Motorola chips except evilbay and you know how that goes,

Brown Dog makes adapters for surface mount but those are 6 and 8 bucks for 14 and 16 pin,

You know the drill. Blowtorch all that junk out, turret board, 5F6a.

well, we do that sometimes, usually with a 5E3 turrent board,

as luck would have it, they do still make those chips, dips,  chains and whips! 

have to leave off the "1" when searching,

So Motorola MC14016B and Motorola MC14053 cross to these TI and Maxim parts for a reasonable cost>

I would bet 18 cents that you can use plain old 1970s CD4053. The MAX4053 has slightly lower Ron and THD, but it's a guitar-amp!

However in a 49 second look DigiKey shows _NO_ stock of CD4053 with proper legs, only SMD fly-specs. It's the end of the world as we knew it.

Must be bundles of 4053 DIP out there, except it is one of those dirt-logic chips which get sanded-down and re-marked as a sexier chip.

CJ said:

So Motorola MC14016B and Motorola MC14053 cross to these TI and Maxim parts for a reasonable cost>

Click to expand...

As far as I know there's only one 4016 in the RD...? no 4053
CD4066 is compatible with CD4016 (lesser Ron IIRC)

took about an hour of eye strain to find the right pdf out of the 20 folders, and another hour to find the illusive chips,

serviced about 5 MM amps and this was the first one with channel switching,

schemo here>

http://www.thetubestore.com/lib/thetubestore/schematics/MusicMan/Musicman-2165-RD-2100-RD-Schematic.pdf

more folders here>

http://www.thetubestore.com/Resources/Music-Man-Schematics

semi BOM

Cimarron Brown Dog

http://cimarrontechnology.com/

Music Man amps are ok to work on but the next guy who brings in a Line 6 rack mount amp or Behringer gets one of these on the house>

CJ said:

took about an hour of eye strain to find the right pdf out of the 20 folders, and another hour to find the illusive chips,

Click to expand...

Of course! a 100RD is not the same as a RD100  :-[

MAX4053 did not exist when these amps were built. (MM founded 1974; chip-amps within a few years; Maxim Inc founded 1983.)

The "B" or A or C after the base number is military to crap temp-range. Nominally the lowest will survive even a hot tube amp, and may be same-as the "better" grades just sold on the cheap.

The chips should be the 13-cent CMOS. The way they are used, there is no advantage in a "lower Ron" chip. The control voltages poke the limits of a low-V MAX40xx chip (but may not explain the death). The design looks fine for sane levels. It may go odd on OVERdrive. If this is your retirement amp, get tubes of 4016 and 4053 for spares. If for a walk-in, replace the chip for 30 days and then snub him.

one of the zener diodes went south so the V max got hammered,

they should add 5 volt regs to allow HC logic chips,

Electronics Surplus has both chips in stock:
http://www.electronicsurplus.com/catalogsearch/result/?cat=0&q=4053

Thanks! we are bookmarking that! 

If that were my amp, I would yank that board and put a dumble OD board set in there.  Make it all tube and retire with 1 amp that can be tweaked and worked on for as long as there are tubes. 

Way more fun and very well documented.  Dumble did it with several MM amps.

Also the head cabinet design is where he got his 4th and 5th gen style from.  Almost carbon copy.