fwphoto Posted January 28, 2012 Share Posted January 28, 2012 I have an original spec. ST-70 that blew a fuse this morning for the first time in maybe a year or two. It blew when I wasn't listening. On weekends I often fire up the stereo on Friday night & leave it on 'till Sunday night when I'm through listening for the weekend. When I found it, I turned everything off & replaced it with a spare. When I turned it back on, tubes got bright fast, there was an audible humm, and the second fuse blew right away. I thought it'd be worth a shot to post something here before I blow another fuse or two. Any thoughts where to start? Frank W. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted January 28, 2012 Share Posted January 28, 2012 you need to have the tubes tested....tubes get gasey with age and short out. next area is having the power supply caps tested. leaving a tube amp on for a whole weekend with seriously cut down on the life of power tubes. Quote Link to comment Share on other sites More sharing options...
fwphoto Posted January 29, 2012 Author Share Posted January 29, 2012 speakerfritz, That's interesting. I recall some debate about leaving tube equipment on, with some pretty much leaving it on all the time. I have no doubt there would be a "cost", but is there also a cost when powering a tube up & down? I guess I figured over the course of a weekend I might use my stereo maybe 4 - 6 time. I'm no expert so I'll take your word for it. Do you think a year or so of occassional, but regular, use like this would cause new tubes to short out? The caps were replaced a year or so ago, too. Do you think they could be bad yet? Thanks for the troubleshooting advise! I'm on it! Frank W. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted January 29, 2012 Share Posted January 29, 2012 so worse case senerio due to differences in the ST70 models and not knowing what mods or upgrades were done. In an ST70, driver tubes last about 5000hrs, power tubes about 2000 - 3000 hrs, rectifier tubes (if not converedt to solid state) about 1000 - 2000 hrs. if you power on and leave on during the weekends, on from riday 6pm to sunday 6pm, thats 48 hrs, times 52 weeks is 2400 hrs, you have been doing this for two years, so 4800 hrs. Even if your tubes were new, and you were using a slow start circut, you passed the life of two rectifier tubes and 1 set of powet tubes and your approaching the end of life of the driver tubes. Assuming of course the tubes were new to start with ( not test like NOS BS) which if you didn't buy from parts express or other large company (not one man part time tube resellers), I would dought. So yes, my bet i the tubes, rectifer def, power tubes depending if they were not russian (russina tubes last 5000 hrs, american and asian tubes last about 40% to 60% of that). Recapping does not mean new caps were added, a lot of folks use old unused caps when recalling (if new production caps were used then OK). so get your tubes tested, and replace as required. as far as leaving gear on all weekend....you should invest in a soft start circut of some type (hard wired into the amp or the black box that you plug you amp into), the black boxes are cheaper. if your tubes checkout good...you can also recheck your bias current using a ditigal meter. Quote Link to comment Share on other sites More sharing options...
fwphoto Posted January 29, 2012 Author Share Posted January 29, 2012 Well, it looks like I'm now starting my real journey into tubes! ;-) My ST-70 is about as stock as you can get. Many of the controls were bypassed when I bought the amp but the mods were all done really well. That made it easy for me to have my tech put it back to "original." New tubes (where needed) & caps (at least that's what I was billed for) & a general refurbishing was done with the ST-70 & a PAS-3. I've been extremely happy thus far. I'm glad I kept my ss amp so, at least, I'm still able to play my music. Thanks for all the info speakerfritz! Frank W. Quote Link to comment Share on other sites More sharing options...
Don Richard Posted January 30, 2012 Share Posted January 30, 2012 Check the all of the filter caps in the power supply for shorts. I have also seen transformers short to ground and do the same thing. Quote Link to comment Share on other sites More sharing options...
Guest davidness Posted January 31, 2012 Share Posted January 31, 2012 Post your question on the Dynaco forum. They, especially Bob Latino, are very helpful there: http://dynacotubeaudio.forumotion.com/f2-basket Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted February 1, 2012 Share Posted February 1, 2012 speakerfritz, That's interesting. I recall some debate about leaving tube equipment on, with some pretty much leaving it on all the time. I have no doubt there would be a "cost", but is there also a cost when powering a tube up & down? I guess I figured over the course of a weekend I might use my stereo maybe 4 - 6 time. I'm no expert so I'll take your word for it. Do you think a year or so of occassional, but regular, use like this would cause new tubes to short out? The caps were replaced a year or so ago, too. Do you think they could be bad yet? Thanks for the troubleshooting advise! I'm on it! Frank W. Much of the stress on tubes occurs when they are first powered up as the filaments draw the greatest amount of current when cold, same as light bulbs. If you're going to use the equipment many times over a weekend, and don't want to turn it on and off multiple times, a good solution is to get a variac and drop the voltage down to around 90 or 95 volts during the idle periods and crank it back to around 117 when you are going to listen. Alternatively, there are soft start devices which you can plug the equipment into which will ramp up the voltage slowly thereby reducing the turn-on surges. Quote Link to comment Share on other sites More sharing options...
leftwinger57 Posted February 1, 2012 Share Posted February 1, 2012 Frank, I thought it was also interesting that to a man at the Polk site they all said they leave their tubes amps on all the time. Me I own solid state which I do not leave on .I was under the impression that the you would burn out something or shorten the life .Well according to these guys, no. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted February 1, 2012 Share Posted February 1, 2012 Much of the stress on tubes occurs when they are first powered up as the filaments draw the greatest amount of current when cold, same as light bulbs. nope.....tube end of life is as a result of the atoms leaving the metals as they pass from filament, pates, grids, etc. The metal surfaces change from whats was smooth, to porous. As they become more porous, fractures occur. As the atoms are releases, gases are generated. The gases lowers the tubes internal impedance. As the impedance's lower, current draw increaes, fuses blow, resistors blow, and ultimately, the tube flames out. Getter extends the life of the tubes by absorbing gas. Getter requires an optimal heat range to work correctly. Some times exhausted gassy tubes have shiney new getter. The tubes were too cool for the getter to work correctly (I have 9 tubes like this...they all look new..tubes are below 50% ratings). So no, leaving tubes on does not extend or enhance their life, it shortens it. Have them tested and you fill find they are high in gas, low in transconductance, and in some cases, higher incidences of shorts. The issue about reducing turn on surges is a seperate issue. A new tube has less porous surfaces and less fractures so it is less likely to flame out on startup. A used tube has more porous surfaces and fractures and is more likely to flame out. The important aspect of tube performance is it's remaining life based on it's decaying Gm and Mu performance. Once the tube drops to 65% performance, keeping it alive by taking on measures to extend it's filament life is not the same thing as replacing an old used tube with a new one with the correct Gm and Mu ratings. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 1, 2012 Share Posted February 1, 2012 tubes get gasey with age Wow, I'm a tube. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted February 1, 2012 Share Posted February 1, 2012 Much of the stress on tubes occurs when they are first powered up as the filaments draw the greatest amount of current when cold, same as light bulbs. nope.....tube end of life is as a result of the atoms leaving the metals as they pass from filament, pates, grids, etc. The metal surfaces change from whats was smooth, to porous. As they become more porous, fractures occur. As the atoms are releases, gases are generated. The gases lowers the tubes internal impedance. As the impedance's lower, current draw increaes, fuses blow, resistors blow, and ultimately, the tube flames out. Getter extends the life of the tubes by absorbing gas. Getter requires an optimal heat range to work correctly. Some times exhausted gassy tubes have shiney new getter. The tubes were too cool for the getter to work correctly (I have 9 tubes like this...they all look new..tubes are below 50% ratings). So no, leaving tubes on does not extend or enhance their life, it shortens it. Have them tested and you fill find they are high in gas, low in transconductance, and in some cases, higher incidences of shorts. The issue about reducing turn on surges is a seperate issue. A new tube has less porous surfaces and less fractures so it is less likely to flame out on startup. A used tube has more porous surfaces and fractures and is more likely to flame out. The important aspect of tube performance is it's remaining life based on it's decaying Gm and Mu performance. Once the tube drops to 65% performance, keeping it alive by taking on measures to extend it's filament life is not the same thing as replacing an old used tube with a new one with the correct Gm and Mu ratings. We're not exactly talking about the same thing (and, yes, controlling the filament inrush surge absolutely affects the tube's life span!) The lifetime of a tube is largely dependent on the lifetime of its cathode emission which, in the case of indirectly heated types, is dependent on the filament's operating temperature. By using a variac to drop the filament voltage (as well as the other electrode voltages/currents) to around 20% below its designated value, tube life can be greatly extended. Of course, you don't want to make it too low as that can shorten life depending on the material from which the filament is constructed. The other issue which may be at play in this gentleman's amp is the powerline voltage which often results in the 6.3 volt tubes seeing 7+ volts (and higher than rated plate/screen voltages) which can greatly decrease life. There are homes in my area which have line voltages of 125. Also, the temperature of the tube bulb is another area of concern for longevity as it affects the tube's ability to dissipate the generated heat. In any amplifier, keeping the output tubes extremely well ventilated either by having them out in the open, or using a fan can make a huge difference. Try comparing the life of say 6L6s under the conditions I've outlined and you will find enormous differences in life span. Quote Link to comment Share on other sites More sharing options...
fwphoto Posted February 3, 2012 Author Share Posted February 3, 2012 Thanks for all the replies! Lots to think about over the weekend while I move the Marantz into play as, at least, a replacement amp for the ST-70. Haven't done that in awhile so it should make for some interesting listening! Unless I happen to find a short or something else directly repairable, I'll start my search for somewhere to test the tubes. I live out in the country so I might be lookin' for a little while. Anyone have a suggestion in northcental/northeast Ohio? I'll be in Cincinnati in a couple weeks, too, so, anything around there? Thanks again! Frank W. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted February 3, 2012 Share Posted February 3, 2012 To find a place that will test tubes...check with music supply stores that cater to musical guitar tube amps. Craigslist will often list folks who can trouble shoot gear. You can also post a new thread to see if there is a forum member in your area with a tube tester. I have one, but I am in NYC. Quote Link to comment Share on other sites More sharing options...
Southern Posted February 9, 2012 Share Posted February 9, 2012 I also have a stock ST-70 and my experience is that the rectifier tube has the shortest life. My experience is that a bad rectifier tube will also blow fuses. As suggested, test your tubes. Quote Link to comment Share on other sites More sharing options...
fwphoto Posted February 12, 2012 Author Share Posted February 12, 2012 Thanks Southern, Still haven't found the time/place to test my tubes yet. I'll make sure to take them all, not just power tubes. Its been fun listening to my old Marantz in the meantime, though. Very different, of course, but better than I remembered. ;-) Take care, Frank W. Quote Link to comment Share on other sites More sharing options...
davis419b Posted February 12, 2012 Share Posted February 12, 2012 It might be snake oil but I have read somewhere that it is not good for to amps to be on without a signal going through them. Quote Link to comment Share on other sites More sharing options...
fwphoto Posted February 12, 2012 Author Share Posted February 12, 2012 It might be snake oil but I have read somewhere that it is not good for to amps to be on without a signal going through them. Thats interesting. I've not heard that before. Once I get the ST-70 back online I think I'll change my habits regarding power up & down. I suppose I can just listen more, too. :-) Frank W. Quote Link to comment Share on other sites More sharing options...
davis419b Posted February 12, 2012 Share Posted February 12, 2012 I always turn my tube preamp on and let it warm and then turn my amps on for about 5 minutes before listening to them. One time with my pCats I went through this procedure and then got a phone call and forgot about the amps. When I came back the amps had shut down, I simply turned them off for a few minutes and then turned them back on and waited the 5 minutes and no problems as they fired right back up Quote Link to comment Share on other sites More sharing options...
fwphoto Posted February 13, 2012 Author Share Posted February 13, 2012 Never heard pCats, but if I had the dough . . . :-) Frank W. Quote Link to comment Share on other sites More sharing options...
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