Hi All,
I have a 100B that has recently died on me, completely not even the Led lights up. I have used it sparingly in the winter months for 3 or 4 years with no issues, except for a broken biasing resistor replacement, since new due my climate heat the rest of the year. This year when I went to use it there was a minor light flickering in KT88 V4 and the unit went dead. The color of the flickering light was strange in color, but can't put it into words due to failing memory, age don't you know. I took the bottom off and couldn't see anything amiss and left it at that for now. I am pretty good at SS troubleshooting and repair so I would like to work on this unit to get it up and running again, but valves are new to me and I will need help with this. Are there any members out there that have experience with these Yaqin units that are willing to help guide me? It will be much appreciated. Note though that I don't have access to the internet at home so I may be slow responding to thread replies.
Thanks in advance.
I have a 100B that has recently died on me, completely not even the Led lights up. I have used it sparingly in the winter months for 3 or 4 years with no issues, except for a broken biasing resistor replacement, since new due my climate heat the rest of the year. This year when I went to use it there was a minor light flickering in KT88 V4 and the unit went dead. The color of the flickering light was strange in color, but can't put it into words due to failing memory, age don't you know. I took the bottom off and couldn't see anything amiss and left it at that for now. I am pretty good at SS troubleshooting and repair so I would like to work on this unit to get it up and running again, but valves are new to me and I will need help with this. Are there any members out there that have experience with these Yaqin units that are willing to help guide me? It will be much appreciated. Note though that I don't have access to the internet at home so I may be slow responding to thread replies.
Thanks in advance.
Really you need access to a tube tester. To start with. Bias probes help also. A good Fluke model 77. You will need all of this and help from members on this forum.
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You checked the fuses? The anode fuse circuit was burned probably the main supply fuse too. You must replace the defective KT88 tube.
Comments as per vidax, what catches many folks out is where the mains fuse is. You have to remove the power input plug and then pull out the small plastic drawer above where the plug went in. It can be tricky as the drawer is retained by the internal fuse sitting in the clips provided. A sharp point or pen knife blade should help. Later 100b's have B+ fuses for each channel, these are mounted on the rear panel. If you do not have them then it is quite possible that a faulty KT88 has taken out the main power fuse. It could be any one of the KT88's which is where a tube tester comes in handy to prevent further fuse blowing as you are otherwise going to have to find the bad tube by trial and error. Hope you get it sorted soon.
Most likely the defect tube is the one who made light flame (V4). My advice is to replace it first if you have not a tube tester.
First off, thank you all for the good feedback info.
I have been thinking about getting a tube tester, or at least building a simple one. I have seen a DIY one on the internet that looks promising. I will look into the bias probe while I am at it. I have some basic testing equipment, DMM, oscilloscope, signal generator, RF generator, and an old Triple transistor tester.
I did try to find the fuse, and if that is where it is, that is diabolical. I will check again this weekend. One thing I noted on all the tubes is that it looks like there was rust forming on the metal base between the glass and base. Probably due to infrequent use, maybe the cause to the tube(s) going bad?
Will check back in with further findings.
I have been thinking about getting a tube tester, or at least building a simple one. I have seen a DIY one on the internet that looks promising. I will look into the bias probe while I am at it. I have some basic testing equipment, DMM, oscilloscope, signal generator, RF generator, and an old Triple transistor tester.
I did try to find the fuse, and if that is where it is, that is diabolical. I will check again this weekend. One thing I noted on all the tubes is that it looks like there was rust forming on the metal base between the glass and base. Probably due to infrequent use, maybe the cause to the tube(s) going bad?
Will check back in with further findings.
I purchased a Sencore Continental 150 II. It was calibrated when I purchased it also. It doesn't give TV-7 type numbers. But is a great all around tester. For emissions, mutual conductance and tube life. Simple to use, and is not an antique by any means.
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I'll give you too an information. I bought from "RadioElec", France two kits:
1. Vacuum tube analyzer curve tracer,
2. Vacuum tube tester full kit with LCD display.
I'm working to install them in a box, both in the same box. IMO they are are very useful and inexpensive.
1. Vacuum tube analyzer curve tracer,
2. Vacuum tube tester full kit with LCD display.
I'm working to install them in a box, both in the same box. IMO they are are very useful and inexpensive.
Hi_Q thanks for the location pic, I would never have found it. The fuse was blown.
The V4 is definatelly bad, I took it out and into sunlight and I see bits of loose greyish metal in the interior. Since all 4 tubes have rust on the metal sleeves I am thinking time to replace them all.
The V4 is definatelly bad, I took it out and into sunlight and I see bits of loose greyish metal in the interior. Since all 4 tubes have rust on the metal sleeves I am thinking time to replace them all.
I bought a matched Quad set of Electro Harmonics KT88s just to test for the soundness of the amp. Not too expensive and I think I may try moding the amp so in case I goof I won't be sacrificing good tubes.
Anyway, thanks again to you all for the help. It was really appreciated.
Anyway, thanks again to you all for the help. It was really appreciated.
I have only Magnepan speakers, so bass is only ok no matter what I use for for amp, but heard these tubes are ok and good enough for temp use.
Just a follow up on the EH tubes. We have been having a cool run of weather so I have been listening to the EH KT88s. First thing I noticed is that on turn on I don't get the slight twang and hum of the original OEMs. Second thing was that although I was diligent at setting bias frequently, when I tested the with the new tubes in all the readings were up from the OEM of .56mV to .9mv and higher with the new tubes in so I dialed them back to spec.
Sound wise, they were better imaging, more detailed and better and more controlled of the bottom end. My overall impression is that the amp was better sounding with these than with the OEMs. For the price of about $100.00 plus shipping a good replacement option. Just my .02 for anyone who is looking for replacements on a budget.
Thanks again for the help.
Sound wise, they were better imaging, more detailed and better and more controlled of the bottom end. My overall impression is that the amp was better sounding with these than with the OEMs. For the price of about $100.00 plus shipping a good replacement option. Just my .02 for anyone who is looking for replacements on a budget.
Thanks again for the help.
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