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I have a problem with my Fisher X-100 amp that just returned form the shop. I have attached a photo of my bill noting the items replaced. About 30 seconds after turn-on the right channel fades out over a period of about 10 seconds until it is completely gone. This happens with all inputs and with 4, 8, and 16 ohm taps.
I have switched all tubes from right-to-left, cleaned all tube pins and sockets, cleaned and lifted the Spacexpander jumpers so they are not shorting, cleaned all the switches and rocked them after the right channel fades, but none of this has had any effect. The left channel continues to be fine even after swapping in the right channel tubes.
On initial turn-on there is some hissing noise in the right channel. Oddly, the right channel returns if I pull the AC plug when the unit is on and it stays on for another 30 seconds after plugging the unit back in.
Any ideas on what I should check next?
Follow Ups:
When your tech or anyone replaces resistors,caps,or wires that hook to tube sockets,he may not have let the solder flow all the way down on the pin of the socket and that will cause those issues..It is very common for this whenever you replace lots of parts..Changing the sockets is unnecessary but reflowing the solder is..Also,make sure he cleaned all the switches because I have seen that act like a tube problem as well. The 3rd common thing to happen when you change parts is,one of the leads of the new resistors or caps may be touching the leads of components on an adjacent tube pin.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 07/03/16
First of all - thank you for the advice.
Second, an update - it may or may not be fixed.
I scrubbed all four 12AX7 sockets with a dental brush using 91% isopropyl alcohol and then used a safety pin to retension them. I also cleaned the tube pins with the alcohol.
After reinserting the tubes I got no right channel at all - even at startup. I wiggled the two right-channel 12AX7's and got some noise when moving the left one around, so I shut down an switched the two. The right channel came back on the next power-on and has not faded since in approximately a dozen turn-on cycles and as many hours of listening.
I'm thinking that if it fades again I'll have my tech replace all the 12AX7 sockets. That will be a bummer since he has a minimum 3-month backlog. But I don't mind sending him business since he is good young guy, is local to me, loves vintage tube gear, seems to know what he is doing, and does not charge an arm and a leg. He also thought that the problem might be due to a pin contact issue on the preamp tubes and advised me to wiggle and swap the tubes around if it happened again.
Only do the wiggle thing when you are trying to find the problem. Otherwise don't do it too much because it will loosen the pins.
Retention the pins when ever you "play" with that tube. For now if it's working just kick back and enjoy it. Surprisingly those tube sockets will last longer than you think. But yes I understand the frustration surprise repairs.
Don't let what happened to me happen to you. One day I got so feed up with the constant repairs that I sold EVERYTHING off. I can't even describe what a loss that was both in hard to get GREAT pieces I will never be able to get again but also financially as well.
I took my money and bought some new gear because I wanted a dependable stereo. Just another one of the BIG mistakes I made in audio.
That Fisher sounds better that most anything you can buy today. Hang in there it's worth it!!!!!!!!!!
Charles
Did you try swapping left to right speaker cables? Might not be your amp. Could be the speaker cables or speakers themselves. That would explain why it worked okay at the techs.
Cheers!
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Try removing the 12AX7s. Then, clean the socket contacts with 91%+ isopropanol or DeoxiT, along with a periodontal brush. After cleaning the sockets, retension them. A fine brad will serve, but a dental pick is best, as the retensioning tool.Clean the 12AX7 pins too.
Eli D.
Edits: 07/01/16
Here's a look at the amp from the top.
Did you contact the tech about the issue?
Was a recent repair. Took it in to him and hooked it up to demonstrate the problem. It worked perfectly.
If it worked, as those things will do, then it does sound like a mechanical problem and not an electrical.
one thing you could do is when the channel fades gently wiggle the tube until the volume comes back up. Then you will have your answer - loose pin contact.
Did he retention the pins as suggested?
If not just go on utube and look that up. VERY easy to do and you can get the dental picks from CVS or some similar drug store.
post your finds
charles
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