jt1stcav Posted July 16, 2006 Share Posted July 16, 2006 I think one of my 300Bs is in the process of kicking the bucket![:'(] I'm a tube-noob for the most part and haven't experienced tube failure as of yet (until this morning maybe). I fired up my system just now (9AM), and as my 300B SET stereo power amp just turned on and began to warm, 10 seconds later my left TJ Full Music 300B/n output tube had a pulsating blue floresence glow (real bright blue in the morning light), along with a light popping noise (hum) through the left loudspeaker. I immediately turned my amp off and a minute later decided to switch 300Bs left to right just to see if it was indeed the tube and not the amp's circuitry (bad cap, etc...I'm not technically inclined). After switching the 300Bs, I turned my amp back on, and within a 10 second warming up period, the same exact tube (now in the right channel socket) did the very same thing! So after a few seconds, I again turned my amp off (along with the rest of the system). I'm assuming that particular 300B tube is going bad and not a component inside the amp itself that's making this tube act the way it is. Am I even remotely close with this guess?Because I'm not electrically inclined, why would this output tube be going bad in the first place? Even for the few seconds this tube was acting up, did it cause any damage to the caps, trannies, and other parts within the amp's circuitry? If I was to replace both TJ 300B mesh anode globes with another pair of matched 300Bs, would the very same thing happen again? Bottom line...is my amplifier damaged now due to this problematic tube, or is my amp the possible cause for this tube going south? I haven't a clue what to do next (except NOT to turn my system on), and I don't have the spare coin to be buying 300Bs left and right just to have another tube die on me if the amp's to blame...and I was all excited about trying out my "new" '60s vintage H.H. Scott Stereomaster 370-B tube tuner dammit![]Your thoughts and concerns would be greatly appreciated. Thanks in advance for your time. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted July 16, 2006 Share Posted July 16, 2006 After switching the 300Bs, I turned my amp back on, and within a 10 second warming up period, the same exact tube (now in the right channel socket) did the very same thing! So after a few seconds, I again turned my amp off (along with the rest of the system). I'm assuming that particular 300B tube is going bad and not a component inside the amp itself that's making this tube act the way it is. Am I even remotely close with this guess? Hi Jim Good trouble shooting Jim. I believe you are on the right track since the problem moves channels with the Tube in Question. Does the Good Tube play good in the Left Channel Now? Can't be 100% sure since I'm not there but if the Good Tube acts good in the Left Channel then thats a good indication that everything in that channel is OK. Do you have the ability to Check or Adjust the Bias of the Output Tube in your Amplifier? If so that is the next step to make sure that it is running the Tube within it's designed ranges.Because I'm not electrically inclined, why would this output tube be going bad in the first place? Like anything man makes sometimes we get failures. I'm not sure how reliable the Mesh Plate are since I haven't really looked into them but sometimes manufactures do have some reliability issues and then it could be just a case of bad luck. Good Tubes for the most part are very reliable and will give many years of service. Even for the few seconds this tube was acting up, did it cause any damage to the caps, trannies, and other parts within the amp's circuitry? My guess is everything is probably OK since you haven't really had a major failure (SHORT!) of the Tube. Again if possible Check/Adjust the Bias if possible on your Amp. If I was to replace both TJ 300B mesh anode globes with another pair of matched 300Bs, would the very same thing happen again? Anything is possible but based on your description I believe you are witnessing the early failure of this particular Tube. Bottom line...is my amplifier damaged now due to this problematic tube, or is my amp the possible cause for this tube going south? Again without being there? but I believe your amp is OK and the Tube is unfortunatly failing prematurely. If you take a 1000 Tubes for example you will have a few that might fail within a very early period while most will go the expected lifetime that they were designed for. mike[] Quote Link to comment Share on other sites More sharing options...
SET12 Posted July 16, 2006 Share Posted July 16, 2006 I am electrically inclined and am very familiar with 300B SETs I saw your Post on Audio Review of your amps they are gorgeous and I never knew that a Graphite Plate 300B is available WOW! I love the sound of it! The fact that you swapped the tube to the other channel and saw the same thing happen says that the tube is likely toast you may or may not be able to go to a music store and have the tube tested depending on what they use to test their tubes many older testers can easily test 300B's but I'd bet it is toast! I don't know if you have a simple multi-meter you can conduct some simple tests. But you should use caution! hopefully the amp has bleeder resistors on its caps so you would give it several minutes to discharge! and carefully remove the cover off take some DC voltage readings of the caps to see they are discharged There is a good chance that it is self biasing which case you'll see a large wattage 800 ohm or so resistor that is near the filament of the 300B you can measure to see if it was damaged you may also measure two smaller resistors 25-100 ohms but you may have a hum pot that actually is attached to the 800 ohm resistor via its center wiper this is important to check this as your bias will run away if it is damaged. It gets a little more complicated to go thru adjustable bias. but depending on its design if you have it, it is likely fine if you have one adjustment but if you have two the pot could be damaged. hopefully you have the non adjustable bias Next is your Output Iron the easist thing to do is check the DC resistance of it's primary it should match the other tranny or be very close to it if the tranny is damaged it will show a lower DC resistance or even be open! Basicly you have one good channel so you can do measurements from one channel to the other I think your 6SJ7's are likely fine So compare parts and let us know what tyou find if your incline to try! SET12 Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 16, 2006 Author Share Posted July 16, 2006 Thanks for your advice, Mike. To answer your first question, yes, the good tube did operate normally (as far as I can tell) in the right channel when the left tube began its fits, and vise-versa when the good tube was placed on the left socket. I did not have any music playing at that time, but there was no audible popping of buzz coming from either channel driven by the good tube, so I assume that there was no damage done to the original left channel when I first powered up my system (and to the right channel afterwards when I switched both tubes). My BEZ Model T3B single-ended amp has no bias adjustments for the user...just plug 'n' play using matched pairs of output (300Bs) and driver (6K7Gs) tubes, along with a rectifier (GZ37). Therefor with the bad tube acting bad in both channels, the good tube appeared to operate normally in both channels each time, thus omitting that anything bad happened to the components inside the amp (I hope)! You're right about premature tube failure, obviously...like light bulbs, there's no telling when one will go bad on you, I suppose. Quote Link to comment Share on other sites More sharing options...
SET12 Posted July 16, 2006 Share Posted July 16, 2006 Yes, I think chances are everything is fine! But that Bias Resistor is a critical part I would check it! Even with a chessy meter you can measure it directly across it! One of my friends had a Cary that lost a 2A3 that took his out! SET12 Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 16, 2006 Author Share Posted July 16, 2006 SET12, thanks for your reply, and for the compliment. I had forgotten all about the gallery pics I posted on AudioREVIEW's site quite some time ago. Yes, my amp came with stock Shuguang graphite anode 300Bs (beefy lookin' suckers) that to my ears sounded pretty good. Erik Mandaville owns them now, powering his DIY 300B monoblocks, and he's quite impressed with their sound as well. Dammit, I wish I had the amplitude to work on electronics, even simple tests escape me! Plus not having a basic multimeter on hand keeps me from exploring my amp's innards, and I probably wouldn't understand what settings to use, or what the readings even meant during testing! All I do know is I do not have to adjust the bias on my SET amp, which is the reason for having to buy matched duets for both output and driver tubes(?). Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 16, 2006 Author Share Posted July 16, 2006 The Model T3B's schematic... Quote Link to comment Share on other sites More sharing options...
SET12 Posted July 16, 2006 Share Posted July 16, 2006 SET12, thanks for your reply, and for the compliment. I had forgotten all about the gallery pics I posted on AudioREVIEW's site quite some time ago. Yes, my amp came with stock Shuguang graphite anode 300Bs (beefy lookin' suckers) that to my ears sounded pretty good. Erik Mandaville owns them now, powering his DIY 300B monoblocks, and he's quite impressed with their sound as well. Dammit, I wish I had the amplitude to work on electronics, even simple tests escape me! Plus not having a basic multimeter on hand keeps me from exploring my amp's innards, and I probably wouldn't understand what settings to use, or what the readings even meant during testing! All I do know is I do not have to adjust the bias on my SET amp, which is the reason for having to buy matched duets for both output and driver tubes(?). Hey, You got to start some where! It takes time to become a wizard at this a stuff but you can learn! At www.diyaudio,com the have a mini courses on tube theory! this is one of t5he largest DIY site in the world I am a member using the same screen name SET12 Also for a few laughs and some basic safety lot of pics he can recommend some meters there is a site called www.tubelab.com this guy is an Electrical Engineer with a Masters Degree he looks like gorilla, a tuff guy with fur but he knows tubes. And is a member of DIY I got a copy of your schematic lucky it prints better than what it shows up as on my monitor you can have a ball with this amp I see 3 mods that I would do in a heart beat! but I can help you keep it running! the first thing to do is buy some 8 ohm 20 watt non inductive resistors from radio shack these you use as a load for the outputs when you have them running with out speakers and are taking live measurements I also know color code and how to look at sockets for pin outs along with alot of safety. The cathode resistors are really heavy duty for the 300B so it would be pretty hard to damage them but not impossible! they are a pair of 7.5 watt 2000 ohm resistors for a totall of 15 watts of dissapation with a proper idleing 300B they are heated to 3.6 watts a good safty margine. You might pick up a basic RCA tube manaul reprint I learned how to design my first preamp from it! For safty I'd try a set of cheap Sovtecks to have on hand for back up! SET12 feel free to contact me any time! Quote Link to comment Share on other sites More sharing options...
mike stehr Posted July 16, 2006 Share Posted July 16, 2006 I still question the reliability of the cathode/filament structures for the TJ tubes...... Jim, your brother has to have a multimeter of some sort. If you look at the schematic you posted, the spot between the two 39 ohm resistors off the 300B filaments, and the 2K bias resistor with the caps bypassed to ground, indicates 60 volts. The 2k bias resistor shows a 220 uF electrolytic with a 2.2 uF bi-polar of some sort bypassed across it. Flip the amp over, and chase that spot out. Shouldn't be difficult at all. Put the positive lead of the multimeter on that spot to check for that voltage, with the negative lead to ground. Make sure the amp is drained of voltage, hook up the leads and power it up. And watch the bias voltage. I'm bettin' that TJ tube's emission is low and not even close to 60 volts, probably in the lower 50 volt range. I mounted some test point jacks to the chassis for testing bias voltage on the fly. I got sick of flipping the amp over.....might be a thought. One of my solid plate TJ 2.5 volt 300B's did the same thing pretty much. No fancy blue light show, just a pop now and then that became more frequent. Checked the bias voltage, and the tube was around 47 volts, where the usual bias was 57 volts. I've been using Sovtek 2A3's for well over a year, and the bias on these hasn't budged. The TJ's I have are nice sounding tubes, too bad..... Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 16, 2006 Share Posted July 16, 2006 Jim: First: You have to be extremely careful doing anything inside that amp. Even though it's off and hopefully unplugged, the filter capacitors can still hold a very strong charge unless they've been bled-off. Working around that tube socket can be a hazard, too. I'm sorry to hear about that tube! Please let me return the tubes you sent me so you can have them as a backup if needed, okay? Honestly, I've enjoyed them very much, and they inspired the design of a very nice sounding pair of 300B amps using the Moondogs, but I have another pair of amps here (Wright 2A3 SETs) that I finished woring on last week. I have permission to use them a little longer, which is nice because they are GREAT little amps. I really doubt you did anything at all to that channel of the amp or any part of the circuit. But it might be a good idea to have some basic things checked on it. Your dad could also test that tube for you, including for internal shorts and noise. I'd be also be happy to help with your amp, and can send you another very nice (and small) 4 watt single-ended stereo amp to use in the meantime. I will need your address so I can send the others back. If you can PM or email that to me, I can try to get them out tomorrow. I'm beginning a week long seminar, but can stop to ship them in the afternoon, hopefully. Erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 16, 2006 Share Posted July 16, 2006 Mike: "and the 2K bias resistor " I think that might actually be 1K, since it appears there are two (X2) in parallel. Erik Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 16, 2006 Author Share Posted July 16, 2006 SET12 and Mike, I want you both to know how pleased I am that you'd offer your assistance to help me troubleshoot the amp. Believe me, all through my childhood and teen years my dad has tried to teach me basic electronics to no avail...I just couldn't grasp it no matter how simplistic he'd make it. Once I realized I wasn't going to learn the essence of electronic circuitry no matter how hard I tried, I pretty much gave up on it altogether. And when my bro sold his Consonance integrated tube amp, he also threw in his multimeter as part of the package IIRC. If not, then I haven't seen it anywhere for quite some time. Erik, thank you for your offer of sending me back my old Shuguang 300Bs to use, but they're for your monoblocks now...plus I just won an eBay auction on a new pair of Electro Harmonix 300Bs on the cheap, so I can use those for the time being when the amp is back up and running. And as far as a spare amp to use I have my other brother's original digital Sonic Impact T-amp that I can hook up to my system...I still want to try out the H.H. Scott 370-B stereo FM tube tuner I just aquired, but it'll have to be next weekend now.[] Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 16, 2006 Share Posted July 16, 2006 Jim: Please check for a PM when you can. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 16, 2006 Share Posted July 16, 2006 Well, that didn't work. Let me try again later or email. E Quote Link to comment Share on other sites More sharing options...
3dzapper Posted July 16, 2006 Share Posted July 16, 2006 Jim, The chance that the tube going bad did any damage to your amp in so short a time is remote. When you get your new tubes, just put them in, sit back and enjoy the music. One caveat I have found with the EH300bs, they take a hundred hours to break in and sound their best. Rick Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 16, 2006 Author Share Posted July 16, 2006 Well then, Rick...sounds like I have alot of music to listen to then, don't I?[] I do hope you're right though...each time the defective tube began to flicker that blue florescence glow and pulsate/pop/click, it was for about 2 seconds at the very most each time before I killed the power, and hopefully not long enough to affect the drivers, the good 300B, and/or the circuitry inside. Erik, I'll be looking for your e-mail later on...[:|] Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 17, 2006 Share Posted July 17, 2006 Jim: It's not a big deal, just trying to help work out something with those tubes you sent me. ....PMs aren't working here for some reason. They keep hanging up. Erik Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 17, 2006 Author Share Posted July 17, 2006 Erik, forget the tubes, really. I appreciate the thought. But I will e-mail you later this evening after work. Later.[] Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 17, 2006 Author Share Posted July 17, 2006 E-mail's been sent, Erik. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 22, 2006 Author Share Posted July 22, 2006 Just wanted to thank everyone for their help and expertise on this matter. I finally received a new matched pair of inexpensive Electro Harmonix 300B EH output tubes to replace the TJs, and I'm happy to report the amplifier's operating flawlessly with the new tubes in place. Apparently there was no damage done to the amp's circuitry or remaining drivers and rectifier. And for their bargain pricetag, these 300B EHs sound pretty darn good to me...should be interesting to hear how they open up once they're broken in for 100 hours or more! Thanks again![] Quote Link to comment Share on other sites More sharing options...
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