st. patrick Posted August 23, 2009 Share Posted August 23, 2009 I am sitting here listening to a MC 240, and noticed that 2 of the small tubes are not glowing . . . . but hot to the touch. It is daylight, but i can see the orange glow in all the others. So, if a tube in an amp goes bad, will it stop playing or will there just be a degradation in the sound?? If it matters, the 2 are a 12BH7 and a 12 AU7. Okay, maybe it is the questioner rather than the question that is dumb . . . . . . but either way I'd like a little guidance. Thanks again, you tube dude gurus, Patrick Quote Link to comment Share on other sites More sharing options...
Audible Nectar Posted August 23, 2009 Share Posted August 23, 2009 Not a tech here, but I have two pairs of MC30s and can tell you that no rod glow on the smalls is unusual. Something doesn't seem right. Have you done any rolling on those tubes, or maybe one of them got bumped a bit? It could be that one of the pins has a poor contact with the socket. If you have used the amp for some time and this is a recent "change" in condition (tubes no longer glowing), they might just be worn out. If you have known good spares or can test your tubes that might tell us something, too. But if those rods aren't glowing, something's amiss. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted August 23, 2009 Share Posted August 23, 2009 The orange glow is the heater in the tubes in your amp and sometimes in the smaller tubes the view of it can be obscured by the getter flash residue deposited on the glass of the tube when it was produced. This is normal and nothing to worry about. When a tube is manufactured the manufacturer will fire the getter (usually round or square shaped element in the tube) which causes a black,greyish or silver deposit on the glass envelope of the tube. If you look at the tube in the dark you can sometimes still see a little of the heater glow from at the bottom of the tube's internal structure were the pin wires reach up to the tube elements. mike tn Quote Link to comment Share on other sites More sharing options...
st. patrick Posted August 24, 2009 Author Share Posted August 24, 2009 I looked at it again last evening (ie, in the dark) and there is an orange glow, but certainly on the faint end of the spectrum . . . . Quote Link to comment Share on other sites More sharing options...
mark1101 Posted August 24, 2009 Share Posted August 24, 2009 To answer your other question..........tubes can fail instananeously and sometimes do (in grand fashion even). However, the larger power tubes and rectifier tubes tend to do this more often than the small signal driver tubes you are concerned with. But......the majority of the time most tubes just wear out gradually and degradate over time. This is why it is handy to have a tube tester available. McIntosh tube amps have traditionally been designed to be very easy on the tubes. In other words tubes last a very long time in Mac amps. Quote Link to comment Share on other sites More sharing options...
st. patrick Posted August 24, 2009 Author Share Posted August 24, 2009 Mark, thank you. The 2 in question are still branded McIntosh . . . but I have no idea how long it has been in there, as I only acquired it within the past 5 years . . . . . I appreciate the help. Patrick Quote Link to comment Share on other sites More sharing options...
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