joessportster Posted June 25, 2005 Share Posted June 25, 2005 hello guys i was just setting here listening to some deep purple, and the sound just faded and then stopped looked over the equipment and noticed all the tubes on the amp had went out, everything else is hooked into the same strip and all stayed on so its not the outlet any ideas???????? Joe Quote Link to comment Share on other sites More sharing options...
r.cherry Posted June 25, 2005 Share Posted June 25, 2005 never listen to deep purple before noon again! it's way too much on that old equipment sorry i havn't a clue really, except it sounds like something broke. Quote Link to comment Share on other sites More sharing options...
dubai2000 Posted June 25, 2005 Share Posted June 25, 2005 Have you checked the fuse of your amp? It might be as simple as that. Good luck. Wolfram Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted June 25, 2005 Share Posted June 25, 2005 what Wolfram said. if the fuse is good plug something else into the outlet, see if it is live. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted June 25, 2005 Share Posted June 25, 2005 Yes. Check the fuse. Make sure it is the proper value. If it is blown, replace with one of the proper value. If it continues to blow, reset the bias to specs. If it continues to blow, have the tubes tested --especially for shorts and gas. If it still blows the fuse, you'll need to take it to a good technician. Since it just faded away without a pop or smoke, I doubt if it is a major repair. Hope this helps. DR BILL Quote Link to comment Share on other sites More sharing options...
joessportster Posted June 25, 2005 Author Share Posted June 25, 2005 ok so the fuse is blown, (i didnt realize the dynaco even had a fuse)guess i should pay a little more attention. Anyway i bought this as a total rebuilt amp from craig at nos valves anyone have any ideas as to why a fuse would blow? I set the amp up according to craigs reccomendations and have used it for a couple months now. Seems weird that it would now blow the fuse unless something happened inside the amp or a tube developed a problem. Any ideas??? Joe Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted June 25, 2005 Share Posted June 25, 2005 I wouldn't get too excited about single fuse blowing. Note the date, put in a new one of the correct value and run it. If it blows again contact Craig, see what he sez. He's very responsive about issues with gear he's rebuilt. you might want to re-check bias and observe tubes visually for odd stuff. If one of a group is visibly glowing brighter than the others that's a cause for further investigation. Meanwhile, forget about it and enjoy your music. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted June 25, 2005 Share Posted June 25, 2005 See my previous post. Sometimes tubes "run away" with no warning. I'm betting that you need to re-bias. That's a good idea every six months or so. If the amp lights up after the replaced fuse, look at the tubes in a dark room. If a plate on a power tube has a red glow, you have solved your problem. You are going to have to do a little detective work before anybody can be of much help. DR BILL Quote Link to comment Share on other sites More sharing options...
mike stehr Posted June 25, 2005 Share Posted June 25, 2005 If one side happened to have a tube or both output tubes in thermal runaway, wouldn't that side start to sound pinched and real bad? I guess it may depend on how bad the runaway is....dunno... I've had power fuses blow from a lousy loose connection in a wall socket. Quote Link to comment Share on other sites More sharing options...
Southern Posted June 25, 2005 Share Posted June 25, 2005 Make sure you match the output of the Dynaco for the correct impedance of your speakers. (8 ohm speakers should be connected to the 8 ohm output on the Dynaco.) Quote Link to comment Share on other sites More sharing options...
pauln Posted June 26, 2005 Share Posted June 26, 2005 What Deep Purple were you listening to? Machine Head? Quote Link to comment Share on other sites More sharing options...
scott0527 Posted June 26, 2005 Share Posted June 26, 2005 Could also be a bad rectifier tube. My st70 was blowing fuses after the rectifier tube finally bit the dust. I replaced it with a new 5AR4(GZ34) and it's been running fine ever since. The rectifiers don't go bad often but it does happen. Quote Link to comment Share on other sites More sharing options...
joessportster Posted June 26, 2005 Author Share Posted June 26, 2005 i replaced the fuse and all seems well the bias was a little off not enough to cause a problem i wouldnt think, i havent heard any distortion at all no matter the level, i have the amp hooked to my scalas, and they are hooked to the 8 ohm leads, i was listening to smoke on the water, off machine head (awsome album i must say)thanks for all the info nice to have a place to get advice Joe Quote Link to comment Share on other sites More sharing options...
Southern Posted June 26, 2005 Share Posted June 26, 2005 Glad to hear that you are back in business. My Dynaco 70 amp blew the 3 amp fuse when I had them hooked to my Forte's. I had the amp turned up and it played fine for about 1 1/2 hours then the fuse blew. I thought it was due to having my speakers hooked up to the 4 ohm output instead of the 8 ohm output, but I think that the amp got a little too hot. Quote Link to comment Share on other sites More sharing options...
archangele Posted July 2, 2005 Share Posted July 2, 2005 Hi, A tube amp should not blow fuses just because it is a bit warm, or it is being played loud. Has this amp been rebuilt or does it still have all it's original coupling capacitors and bias power supply components? Any vintage tube amp must be completely gone through by a competent tube amp technician before it will be reliable. Things like the weakening over time of the selenium bias rectifier or the slight DC leakage through an old coupling capacitor can cause an over current condition which will blow the fuse. The number one reason for blowing fuses in amps like the Dynaco ST70 is the 5AR4 rectifier arcing. Chinese 5AR4's are notorious for this. Having your amp biased too hot (too much plate current) can cause the fuse to fail. A shorted output tube will certainly cause a fuse to blow. Do NOT use a larger fuse then the amp specifies!!!If it says to use a 3 amp fuse and it will not run long with a 3 amp fuse in the fuse holder, something is wrong with the amp. Installing a 4 amp fuse will only mask the problem and will most probably lead to a major problem. The next most common problem with a vintage tube amp is the main B+ power supply. Again, in the Dynaco ST70, the 'quad cap", that big 3" x 1.5" silver cylinder next to the 5AR4 rectifier tube can develop a mild short. It will still work, but it will get worse and worse till it loads the power transformer enough to cause the fuse to blow. It generally starts out by blowing a fuse every so often. Then as it gets worse, you find that you are replacing a fuse almost every time you use the amp. Anyway, these are a few of the problems you may have. But fear not, all this stuff can be repaired and is generally not fatal if taken care of before you see smoke. Bill B. Vacuum tube Hifi and Guitar amp repair, design and building at: http://home.alltel.net/wbittle1 Quote Link to comment Share on other sites More sharing options...
joessportster Posted July 4, 2005 Author Share Posted July 4, 2005 the amp was completely rebuilt and upgraded (moded) by a very competant member of this forum (craig at NOS Valves) it is under a warranty as well thanks for the info Joe Quote Link to comment Share on other sites More sharing options...
joessportster Posted July 4, 2005 Author Share Posted July 4, 2005 the amp was completely rebuilt and upgraded (moded) by a very competant member of this forum (craig at NOS Valves) it is under a warranty as well thanks for the info Joe Quote Link to comment Share on other sites More sharing options...
archangele Posted July 4, 2005 Share Posted July 4, 2005 the amp was completely rebuilt and upgraded (moded) by a very competant member of this forum (craig at NOS Valves) it is under a warranty as well thanks for the info Joe ---------------- If it keeps giving you problems you may want to let Craig have a look at it again. What mods were made to it? There is always the chance that one of the new components failed. This happens. Craig is a good tech. He will be able to figure it out. Bill B. Quote Link to comment Share on other sites More sharing options...
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