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#22
One look at the schematic will show that on this amp, the leg bone is connected to the thigh bone, the thigh bone is connected to the knee bone, and the knee bone is connected to the ankle bone, (which looks like where the problem occurred). Maybe one of the real amp gurus on this forum will be able to tell us if it is just a sprain or a clean break.
 
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#30
I hate bifocals. I was working on a Fender Blues Jr. The B+ lug is right next to one of the heater lugs. I fouled up and accidentally switched them. Not even the tubes were salvageable.
 
#35
ReidK said:
GK MB150 series, yes?

50V caps in an amp that's rated at 100W into 8 ohms? That's cutting it a little close, isn't it?

Reid
Click to expand...

Looks like a rail voltage of +/-45V, at high line of +10% that would be +/-50V which is just about right. I might choose 63V caps but there's nothing inherently wrong with 50V caps. There are a lot of those amps still working just fine.
 
#38
BioWeapon said:
What's wrong with having 50v caps? Their voltage rating is unrelated to power output, and these amps are designed by professionals.
Click to expand...

Actually, voltage rating is very closely related to power output. For a typical class AB amp (and this is not a particularly exotic design as far as I can tell), power output into 8 ohms is determined mainly by the rail voltages (current-carrying capacity of the output devices typically limits power into lower impedances). Rail voltages determine the required voltage rating of the filter caps, and a 100W amp using typical output devices (such as the TIP 36C seen here) will have rail voltages around +/-45V, as agedhorse notes above. I'll reply to his message separetely.

As for being designed by professionals, well, yeah, no kidding, but compromises get made in any product. We aren't talking about a cost-is-no-object, bulletproof mil-spec design here. You can look at almost any mainstream audio product - designed by professionals - and point to areas that aren't very tolerant of over-voltage.

Reid
 
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#39
First, let me make it clear that I'm not blaming the caps for what happened here. It doesn't look like they blew.

agedhorse said:
Looks like a rail voltage of +/-45V, at high line of +10% that would be +/-50V which is just about right. I might choose 63V caps but there's nothing inherently wrong with 50V caps. There are a lot of those amps still working just fine.
Click to expand...

OK, I'm just a little surprised to hear that (though I'm not surprised that you might prefer 63V caps - if you were going to put your name on this amp, would that "might" become more definite?). I've always read that 10% over nominal operating voltage was an absolute minimum, and I'd expect GK to do more than that. Most higher-end amps that I've seen have more like 20-25% headroom in the voltage spec for the first stage filter caps, some have more.

Of course there are a lot of those amps still working fine. I didn't say it was too low, I said "cutting it close", which I still think it is.

Reid
 

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