John EH
08-26-2005, 08:35 PM
Got a Fisher 500C off the bay a few years ago. The seller said it had been checked by a tech but when I got it, it only worked on one side. Put a sig generator on it and the first test point, the tranny was bad.
Had to order a new tranny and I put it in and got the channel back. Real Happy. Never could get anything decent from the FM side and I worked on it roughly the same time I was working up a Dynaco FM3.
About a year ago I finally figured out that there was a tube in the FM3 that didn't belong. I scratched my head then pulled out the schematics and manuals for all the junk I own and pinned it down to the Fisher 500C. Voila, I mixed up some tubes somehow.
Ran the FM for 10 minutes and it would die. I noticed the 6HR6 was ridiculously hot as was one of the Nuvistors 6CW4. Believe it or not when I got the 500C from ebay the guy sent a couple spare tubes and a couple of nuvistors.
Changed the tube and the Nuvistor and now I've got FM full time although I can tell this amp needs an alignment. We have a station where I'm at at 107.7 and I can't nail it. I run into 108 and run out of tuning. I've got a line on an alignment and it'll happen fairly soon.
In the mean time I've ordered some JJ 7591's, and I had a bag full of JAN GE 12AX7's which I put in.
Also I put a rectifier bridge in, changed the coupling caps, and replaced the bias resistors and got the bias at a perfect -17 v. I understand many people bias to -21 and maybe I'll play around with that later. For now things are good.
I've got the 500C hooked to a pair of Wharfedale Diamond 8.1's and an ordinary CDP as a source.
I'm blown the heck away with the quality of the sound I'm getting. I actually did all this to sell it but I don't think I can turn loose of this thing, even though I have WAY too many stereo's as it is.
Thanks for reading............I'm excited about this.
John
Had to order a new tranny and I put it in and got the channel back. Real Happy. Never could get anything decent from the FM side and I worked on it roughly the same time I was working up a Dynaco FM3.
About a year ago I finally figured out that there was a tube in the FM3 that didn't belong. I scratched my head then pulled out the schematics and manuals for all the junk I own and pinned it down to the Fisher 500C. Voila, I mixed up some tubes somehow.
Ran the FM for 10 minutes and it would die. I noticed the 6HR6 was ridiculously hot as was one of the Nuvistors 6CW4. Believe it or not when I got the 500C from ebay the guy sent a couple spare tubes and a couple of nuvistors.
Changed the tube and the Nuvistor and now I've got FM full time although I can tell this amp needs an alignment. We have a station where I'm at at 107.7 and I can't nail it. I run into 108 and run out of tuning. I've got a line on an alignment and it'll happen fairly soon.
In the mean time I've ordered some JJ 7591's, and I had a bag full of JAN GE 12AX7's which I put in.
Also I put a rectifier bridge in, changed the coupling caps, and replaced the bias resistors and got the bias at a perfect -17 v. I understand many people bias to -21 and maybe I'll play around with that later. For now things are good.
I've got the 500C hooked to a pair of Wharfedale Diamond 8.1's and an ordinary CDP as a source.
I'm blown the heck away with the quality of the sound I'm getting. I actually did all this to sell it but I don't think I can turn loose of this thing, even though I have WAY too many stereo's as it is.
Thanks for reading............I'm excited about this.
John