Woodog Posted December 8, 2005 Share Posted December 8, 2005 Need some help <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> Currently on my Klipschorns Im running a Scott 130 Preamp --> 208 Power Amp. I have the same 7591 tubes that came with the amp in Nov. 2003 and listen to it at least 25 hours week. About a month back I heard a hum in the right Khorn and found that one of the 7591 tubes in my Scott 208 looked milky. Replaced it with a spare from a quad that I had bought from a former-forum-member-amp-technician-who-must-not-be-named (any other similarities to Lord Voldemort, other than the ability to use proper grammar, are purely coincidental). Re-biased the tubes, waited a few days, rebiased again, checked after a few days and they were holding steady. Sound was okay but without the clarity of image I was used to. A couple of days ago a LOUD hum came up suddenly on the left Khorn, then the fuse blew on the 208. Rectifier looked dark and smokey, so I figured it was bad, went to my 222-B (badly rebuilt by same tech whose name must not be mentioned. ) and snatched the rectifier tube out of it and used it to replaced the one from my 208. Image clarity was back! Monday - Set bias to 0 and voltage to 32v on both sides. Checked the bias on Tuesday and it had drifted to -.008 on the left and +.022 on the right. Rebiased to 0 and 32v. Wednesday bias had drifted to -.005 on the left and +.033 on the right. Rebiased to 0 and 32v I figure Ive got 2000+ hours on these 7591 tubes which were old to begin with. The condition of the spares may not be great considering the source. Should I just go ahead and get a new set of JJ 7591s? I can get a They seem reasonable enough at $30 a pair at tubedepot.com. I have JJ brand in my 299B and they sound great. Sovtek rectifiers are ~$20, but I think the rectifier from the 222-B is a Mullard 5AR4. It seems clear and the sound is good. I worry that I might be frying tubes though. Or is there a possibility there is some other problem Im not seeing? Thanks in advance. Woo Quote Link to comment Share on other sites More sharing options...
mark1101 Posted December 8, 2005 Share Posted December 8, 2005 Woo, Craig and the other tube techs will be on this later tonight I'm sure. All I wanted to say is that I use the JJ7591s and have had no problems at all and have respectable performance for the last year+ (in my LK-72). They hold their bias settings very well. Prior to te JJs I was using those giant Electro-Harmonex 7591s that butted up against the trannys. I was actually happy with those, but they bothered me how they were "cocked" into the sockets. They sounded a bit better than the JJs (very close), but the JJs are fine. Go for them. Get a spare rectifier tube to have on hand as well. Have fun. Quote Link to comment Share on other sites More sharing options...
Woodog Posted December 8, 2005 Author Share Posted December 8, 2005 Thanks Mark, I ordered a replacement Sovtek 5AR4 for the 299-B after it went bad a few weeks ago and blew a fuse. I could actually see the shorting inside of that tube. I'm thinking the tubes are just needing replacing, but wanted some of the 'heavyweights' to weigh in on this. I tried the search function here before I posted, but didn't find much that helped me out. I heard your LK-72 on the Heresys and it sounded great. I think you had the EH tubes at the time, right?I'm not sure the EH tubes would fit in the 208 very well. the back row is awfully close to the transformers.later,Woo Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 8, 2005 Share Posted December 8, 2005 Woo, Sounds like you may need a new quad of 7591's the JJ Tesla 7591's work great but get them from a reputable seller not off eBay. I like Doug and www.dougstubes.com for the JJ 7591. Another thing you may want to do is clean the tube sockets and retension the C shaped metal contacts inside every pin hoel of the 7591 sockets and the 5AR4. You really the bias drift your describing is horrible but if it keep repeating its a good sign you have some weak tubes if nothing else is going array. God I hope not or you may have to not mention my name[] By the way how's my old 130 doing for you? Craig Quote Link to comment Share on other sites More sharing options...
Woodog Posted December 8, 2005 Author Share Posted December 8, 2005 Thanks Craig... I've gotten good service from tubedepot.com, but I'll check out the site you mention. Your old Scott 130 is a FINE piece of equipment. I still can't believe I won that. (speaking of insane Ebay prices, going the OTHER way, check this out... ebay item # 5836157974) Time to sell mine? ha ha What tool would you suggest for cleaning and/or re-tensioning the pin connections? I guess radio shack contact cleaner will work ok? btw, I'm always bragging on your work. The tech-who-must-not-be-named, well, let's just say I learned a lesson. (if you are new here, here's the lesson... if the majority of folks here who've been around a while consistently give someone a bad time for shoddy work, believe them!) thanks again Craig, Woo Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 8, 2005 Share Posted December 8, 2005 Woo, With all the vintage gear you have you should invest in a can of Caig Deioxit D5 for the tube sockets and RCA jacks and the can of Caig CaiLube MCL to lube the controls. First use the D5 on all the controls, switched, tube sockets and RCA jacks. Then for the switches controls "only" give each a quick squirt of the Cailube. With the controls do both while worked the controls. Do this once a years and the controls and contacts should last your life time. As far as tensioning the tube sockets a nice pointed dental pick type tool will work nicely what you want to do is tighten up the gap in the C so it grabs the tube pins tightly. Parts express sells a little soldering kit that I use for this it onlt costs like $4 Part Number 370-335 Parts Express Caig Products Part Number 341-200 & 341-250 Quote Link to comment Share on other sites More sharing options...
Woodog Posted December 9, 2005 Author Share Posted December 9, 2005 Ordered tubes last night, cleaning supplies today. Thanks Craig! Woo Quote Link to comment Share on other sites More sharing options...
Woodog Posted December 17, 2005 Author Share Posted December 17, 2005 The cleaning solutions and tools arrived on Monday. I spent that night lovin' up on my 355, carefully removing and cleaning sockets, lubing controls, dusting, and in general making it exactly right. I did the same for the 208, pulling the old tubes and cleaning the connections. The new tubes arrived Tuesday, and I plugged them in and put the Scott 355/208 combo back into action while I take the time to do the same to the 130 preamp. Excellent sound! Bias holding rock steady as of this writing. There is something quite therapeutic about taking care of something that gives so much enjoyment. I highly recommend it. Woo Quote Link to comment Share on other sites More sharing options...
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