I'm new here. I'm having problems with my Eros 2 phono pre-amp, and looking for suggestions. First a little history: I purchased the kit approx. 4 years ago. I jumped in and almost finished the kit, but realized I had soldered a piece in the wrong place and would have to re-work the affected areas of the circuit. Then, tragedy hit, my wife of 47 years was instantly killed in a car accident. My life changed dramatically. One of those changes was working on my kit...I let it go. About a year ago, I contacted the Bottlehead queen (Eileen? A nice woman, by the way) and asked her to send a parts kit so I could finish the project, almost from scratch. Again, no motivation, so I enlisted a friend, an audio wizard, who has built Bottlehead kits in the past. He carefully went through the whole kit, reviewed my work, fixed my mistakes, conducted all the power, resistance, and voltage tests. Everything was spot on. I put the pre-amp into my audio system and voila!, I was listening to vinyl records again...like never before, heaven on earth. Beautiful! Anyway, 3 weeks later (about 15 - 20 hours of play time), a fairly loud, low frequency hum/rumble was coming from the left output channel. I checked all my interconnect connections, swapped EF 86 tubes, checked for signal coming from the tonearm, etc. ...nothing helped. Soon, still perplexed, I started to re-look everything, however, the hum disappeared to be replaced with silence...I lost the left channel completely. The right channel was still working wonderfully.
I opened up my assembly manual and started to do my checks for power, resistance, and voltage. Findings: All resistance values where right on. Power supply test: All voltages where perfect. Voltage check: [terminal IA: 217 vDC]; [terminal IB: 102 vDC!]; [terminal OA: 162 vDC]; [terminal OB: 99.8 vDC!]. All other voltages were in proper range. These results validated my problems with the left channel not working. So, I traced the IA and IB wires to the 12AU7A tube, and indeed, the values were the same...low voltage on the IB terminal (D6 tube pin). I rechecked solder joints, made sure wires weren't touching where they weren't supposed to be etc. Frustrated, I let it sit for a few days...OK, actually a week. Things changed when I went back to trouble shooting. The right channel voltage had now dropped. The new values are: [terminal IA: 118 vDC]; [terminal IB: unchanged]; [terminal OA: 115.6 vDC]; [terminal OB; unchanged]. I also noticed that the 12AU7A tube seemed to be generating more heat. I quit the trouble shooting and decided to get some help. Here I am!
Logic/common sense tells me that the tube 12AU7A is failing or failed, However, before I go about replacing tubes, I would like some opinions if this is what I should do as a start.
Thank you for enduring this message.
John Nolan
