nickhuge Posted March 22, 2019 Share Posted March 22, 2019 This has been an issue for 4 years since i bought it second hand and i just don't know what to do I tried to get it fixed by John Kelly but he couldn't find what was wrong Basically, after about 90 minutes in a gig scenario, ie hot venue at decent stage volume, it cuts out. If i turn it back on straight away it won't have any power. if i leave it 20 minutes and turn it back on i might get another 5 minutes out of it. John put a signal generator on with a high load for a couple of days when I tried to get it fixed last but it didn’t cut out at all. It just seems to be in a gigging environment, hot and sweaty. It does it every time which makes it unusable and unsellable. Is this something anyone has heard of and might know what it could be? I have no experience but im wondering if it's a moisture/heat issue and if so whether other people have had this problem. Quote Link to comment Share on other sites More sharing options...
skidder652003 Posted March 22, 2019 Share Posted March 22, 2019 is it one of the vietnam models? Quote Link to comment Share on other sites More sharing options...
nickhuge Posted March 22, 2019 Author Share Posted March 22, 2019 I'm not actually sure this second. I can look when I'm home. Quote Link to comment Share on other sites More sharing options...
itu Posted March 22, 2019 Share Posted March 22, 2019 So a heat related issue, there is a broken connection or soldering somewhere. How about send/return (use a cable)? May be pretty hard to find: if you have an access to a temp camera like FLIR, it may help to try to find the problematic place. Is the speaker in top order? Try a different amp and another cab to exclude the problem. And cables, of course. Quote Link to comment Share on other sites More sharing options...
stevel Posted March 23, 2019 Share Posted March 23, 2019 For a generic overheating problem - is the fan working properly? More specific things to check - when were the valves last replaced? Have you tried other valves to rule out a bad one? Quote Link to comment Share on other sites More sharing options...
tommorichards Posted March 26, 2019 Share Posted March 26, 2019 i'd also check the Fan that Stevel mentioned, as i've had a fan cooled amp in the past that cut out once it got warm, and the amp tech that fixed it said it was the fan being clogged. Being on so long and then causing an issue does point to a temperature issue. Quote Link to comment Share on other sites More sharing options...
Ricky 4000 Posted March 26, 2019 Share Posted March 26, 2019 My B-15(T) used to die out... once or twice during a song it would fade to nothing, then come back after a second or two. No wonder the scumbag who traded it with me was so keen for the deal. 🙁 It probably doesn't help the OP, but our (at the time) studio engineer (bless him) managed to fix it by de-soldering and re-soldering all the connections behind the front panel. It was a guess, as he knew that most faults develop closest to the control knobs and switches. He was right, because it's not done it again in 20-odd years. 👍 Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted March 26, 2019 Share Posted March 26, 2019 When it switches itself off what is the standby fault led doing? The amp has a feature which switches off the high voltage power if there are any faults with the power output valves. With any valve amp you have to suspect the valves first, they aren't components that last forever and they may need replacing. It's also possible that there are problems with the pin connections, you can pull them out and look for signs of corrosion and maybe try a bit of switch cleaner in the sockets. Don't poke around unless you are confident though and only do so with the amp unplugged and rested for a while, there are some nasty voltages in there. Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted March 26, 2019 Share Posted March 26, 2019 Sounds like a flaky joint. I fixed a noisy valve amp just by removing each valve then working it in and out of its socket for a while 🙂 At the weekend I fixed a mixing desk that had developed a mains 'buzz' - I just resoldered every suspect-looking joint in the power supply and it magically went away. The main suspect looked like it had been bad from new. Made me look like an electronics god, but to be honest all I had to do was identify where the regulator circuitry was. 2 Quote Link to comment Share on other sites More sharing options...
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