Marshall MA100H

[themusic]

Looking for a schematic for Marshall MA100H that has voltages on it.
The only one I've found seems to be more like a layout...Thanks

[g1]

Not sure if this is the one you have, it's the only one:
http://music-electronics-forum.com/a...it_diagram.zip
Seems voltages are appearing less and less on schematics.

[Enzo]

I dunno. A couple of thoughts. If you put voltages on there like "350v" on a B+ node, then people expect 350v there. They always ignore that note that used to be on the drawing and if not is implied there: voltages are approximate and may vary 20%. So we get someone posting, "my amp only puts out half as loud as it used to, my B+ only reads 348v, should I replace all my filter caps?"


Sometimes an amp maker will take a good amp and just measure the voltages in it as typical. Same 20% still applies, but now we see schematics with voltage on them like "328v". With a number like that, looks oh so precise, people assume it MUST be precise and so are especially unravelled when it is not exactly that.


Same thing at like triode plates. Not only does the B+ fed to them vary all over the place, but between resistor variations and tube variations, the sample plate voltage can be a wide range and still be perfectly good. But if they print 260v on there, they can count on lots of calls telling them that some amp in the field has 248v on it and maybe "all the filter caps need replacing?"


Wait, my manners are slipping. Hey, themusic, welcome to the forum. My remarks are not made at you, though it could look that way. One of my ongoing themes is that guitar amps are not precision circuits and there is a lot of variation within them. I like to point out that in an amp with typical 480v B+, if it runs on 120v mains power, then every 1 volt of change in the mains coming out your wall socket will result in 4 volts of change in your B+. A 5v spread in mains voltage then is a 20v range of B+ in that amp. And mains voltage changes all the time.

[g1]

So we get someone posting, "my amp only puts out half as loud as it used to, my B+ only reads 348v, should I replace all my filter caps?"

C'mon now, you know without the voltage info they'll still ask if it's the filter caps, right after "is it the transformer?"

[The Dude]

According to "internet wisdom", voltage is not relevant. Don't you just automatically replace ALL of the caps anyway?

[Enzo]

No, first you replace the transformer only to be baffled that "that wasn't it."

Hey, themusic, we are just having some fun, seriously. Can we do anything beyond the schematic g-one posted? I don;t have any other drawings myself.

[The Dude]

Oh yes, hadn't thought of that. Please do not take my comment above as being directed at you themusic. As Enzo said, "just having some fun". Not directed at anyone in particular.