risingjay Posted July 17, 2005 Share Posted July 17, 2005 I have a pair of Dunaco MKIII's that I have just retubed. I'm buring in the tubes right now. I set the bias to the suggested setting of 1.56 volts. My question is, why does the voltage vary when I periodicly check the voltage? It will go up to 1.57 and 1.58, then I reset it to 1.56, come back and can be down to 1.53,1.54. Is this normal? Is it due to other things running in the house say the airconditioner? I'm still learning. Thanks Jason BTW- Just bought the Juicymusic BB Extreme! I get it tomarrow!! Quote Link to comment Share on other sites More sharing options...
risingjay Posted July 17, 2005 Author Share Posted July 17, 2005 Sorry spelling error on Dynaco, so that would be Dynaco Mark III's. I don't care about the rest of the errors. Quote Link to comment Share on other sites More sharing options...
risingjay Posted July 17, 2005 Author Share Posted July 17, 2005 I also have a new matched quad of KT88's. When I turn the lights off, I notice a purplish haze inside. Obviously this is normal. The thing that gets me is that one of the tubes does not produce this purple haze. Is it a bad tube? Should I modify the amp to have a seperate bias for each KT88? And finally, is there a way to regulate the supply on the amp. Mark said it's unregulated. Thanks again all. Quote Link to comment Share on other sites More sharing options...
laurenc319 Posted July 17, 2005 Share Posted July 17, 2005 i see that with my EH KT-88. It's plasma glowing and is normal Quote Link to comment Share on other sites More sharing options...
Audio Flynn Posted July 17, 2005 Share Posted July 17, 2005 Not certain how they were bench tested before you took posession of them. Puting new tubes in an older untested amp can wear them out quick in some circumstances. NOS Valves and other technicians can give them the once over and help assist in making sure they have many years of good life left in them. They should be great wit the Blueberry and CHorus IIs. Fellow Chorus II owner Rick Quote Link to comment Share on other sites More sharing options...
risingjay Posted July 17, 2005 Author Share Posted July 17, 2005 Well, I bought these about a year and a half ago and the were rebuilt 3 yrs ago. I might have those guys go through them anyway. I want the power supply rebuilt and that da*n silver thingy replaced, the board modified, fuse put back to the origanl position, on off switch put back in, and have all binding posts put back in instead of two. The guy previously just put the 8ohm binding posts in leaving out the 6 and 4. They look really good though. I just not sure if I want to do the work myself. It would be awesome to learn, but I do better when someone shows me and explains while I'm working. If there is anyone in the Chicagoland area that is willing to take on a eager student, let me know. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted July 18, 2005 Share Posted July 18, 2005 Mark III's are my favorite amplifiers. Brought up to modern standards and carefully maintained, I believe they will hold their own against all comers. Many of us have replaced the KT-88s for KT90s with stunning results. It is an exact drop-in and biases at the same 1.56v routine. It is a much more robust tube. Some non-NOS KT-88s will experience slightly rosy plates even when precisely biased. I blame this on higher house voltage than the 117vac for which they were designed. In our neighborhood, 128vac is common and I have seen it at 130! I run my Mark IIIs through an ISOTAP to achieve the original 117vac. These show up on E-bay at a bargain and would be a good investment. When the KT88's become tired, try a quad of KT90s. I hope your Mark IIIs bring you as much pleasure as mine have for me. DR BILL Quote Link to comment Share on other sites More sharing options...
risingjay Posted July 20, 2005 Author Share Posted July 20, 2005 ---------------- On 7/18/2005 3:37:08 PM DRBILL wrote: Mark III's are my favorite amplifiers. Brought up to modern standards and carefully maintained, I believe they will hold their own against all comers. Many of us have replaced the KT-88s for KT90s with stunning results. It is an exact drop-in and biases at the same 1.56v routine. It is a much more robust tube. Some non-NOS KT-88s will experience slightly rosy plates even when precisely biased. I blame this on higher house voltage than the 117vac for which they were designed. In our neighborhood, 128vac is common and I have seen it at 130! I run my Mark IIIs through an ISOTAP to achieve the original 117vac. These show up on E-bay at a bargain and would be a good investment. When the KT88's become tired, try a quad of KT90s. I hope your Mark IIIs bring you as much pleasure as mine have for me. DR BILL ---------------- Dr. Bill, What did you do to bring them up to modern standards? Did you bring them to someone? I'm interested in doing this and any help will do. Quote Link to comment Share on other sites More sharing options...
Southern Posted July 20, 2005 Share Posted July 20, 2005 I recently recapped my Dynaco ST-70 amp and PAS-2 pre-amp and replaced the original rectifier with silicon diodes. I live in the Chicago suburbs and would be willing to coach you. Quote Link to comment Share on other sites More sharing options...
Deang Posted July 20, 2005 Share Posted July 20, 2005 Everytime one of you amp techs "coach" me, I end up lit like a Christmas tree with my arse all charred up. Nobody has any business sticking a hand in there unless they know what the hell they're doing. Life is short enough as it is. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted July 21, 2005 Share Posted July 21, 2005 ---------------- On 7/20/2005 6:00:23 PM risingjay wrote: Dr. Bill, What did you do to bring them up to modern standards? Did you bring them to someone? I'm interested in doing this and any help will do. ---------------- No, I do all my own work. In the case of the MARK IIIs, I used Joe Curcio's cap boards. This is a huge improvement over the old electrolytics. It raises the voltage rating to 600vdc. The old electrolytics were driven right up to their maximum and exhibited a high failure rate. I also used Joe's PC driver board which is all triode and gets rid of the 6AN8. THD and IMD are improved by a factor of 10. Not too shabby. In all candor I have to admit that one of the cap boards failed after slightly less than fifteen minutes! It was a shorted capacitor --the very thing that I was trying to avoid. Damage was done to both the cap board AND the driver board. It was just one of those things that happen, a brand new component failed! $50 worth of parts burned open, thus protecting the 3A slo-blo 50¢ fuse. Hmm. The KT90s provided maybe five more watts and made a huge difference in the bass without sacrificing any of the KT88 warmth. So, maybe I made "Stone Soup"! I also used the new power and output transformers. But I DID keep the original chassis (except for the new ceremic sockets)! Anyhow. It kept me out of the pool hall. DR BILL Quote Link to comment Share on other sites More sharing options...
Deang Posted July 21, 2005 Share Posted July 21, 2005 Someday, you'll have to tell us what this means: "Lived in Hope, almost died of despair!" Quote Link to comment Share on other sites More sharing options...
DRBILL Posted July 21, 2005 Share Posted July 21, 2005 ---------------- On 7/21/2005 1:57:37 PM DeanG wrote: Someday, you'll have to tell us what this means: "Lived in Hope, almost died of despair!" ---------------- My first assignment out of seminary was St. Mark's Episcopal in Hope AR in the late 60s. I had the honor of presenting Paul and Belle Klipsch for confirmation. I was their priest until I took my next assignment some six years later. In those days, you couldn't have claimed that Hope was a great cultural center, or garden spot, or center of academics. In a word, think sty. There were some bright spots. Paul and Belle were frequent dinner guests at the Vicarage. Some of us (amost all overeducated and about the same age) formed a monthly dinner club at which the host provided the entré and cocktails and wine and the rest brought the remainder of the meal. There was the two of us; the editor of the Hope Star and his wife; Mac McClarty, who went on the be the Chief of Staff at the White House and his wife; the county recreation director and his wife who was a professonal flautist. Once a month there was intellectual stimulation and lively conversation. Sometimes even music. I had the only 9' concert grand piano in the county! The other bright spot was St. Mark's. It had a pipe organ, Tiffany windows, and a golden interior that looked like the inside of a Russian Easter egg. I could just sit in there for an hour and regain sanity. But the rest of the time, might I say most of the time ---ennui, angst, dispair. In my maturity (dotage?) I could be happy seated on an anthill. Youth is wasted on the young. And that, DeanG, is the rest of the story. DR BILL Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 21, 2005 Share Posted July 21, 2005 What a wonderful story, DRBILL. Quote Link to comment Share on other sites More sharing options...
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