JBryan Posted February 26, 2011 Share Posted February 26, 2011 Well, after 50 years of unrequited service, my Scott 222c (w/original tubes) finally complained. I switched on the power only to see a light show in the 5AR4 rectifier tube. I immediately shut the amp down and tested the tube....its dead. Has anyone else experienced this demise in a rectifier tube? I've never had one go out on me but I always figured it would just not fire up one day - no light show. I also figured that the other tubes would have faded away long before the rectifier - it gives me pause. While I didn't smell any smoke or notice anything else unusual, is there something I should check before installing another 5AR4 and firing the amp up or am I being overly cautious. Would this be a good time to check/adjust the bias? If so, any tips? Thanks in advance for your help. -Bryan Quote Link to comment Share on other sites More sharing options...
Guest " " Posted February 26, 2011 Share Posted February 26, 2011 I would recommend that you have the unit checked out. It's very likely that the failure could be the result of aging components. Quote Link to comment Share on other sites More sharing options...
gnatnoop Posted February 26, 2011 Share Posted February 26, 2011 generally they commit suicide....had one go out on my jma blueberry, it stepped right into the path of a stream of speeding electrons. [] Quote Link to comment Share on other sites More sharing options...
Davecv41 Posted February 27, 2011 Share Posted February 27, 2011 The schematic shows a lot of filter capacitors attached to the cathode at pin 8. Get the amp checked and recapped if it hasn't been yet. The selenium rectifier looks like a good candidate to be replaced at the same time. Quote Link to comment Share on other sites More sharing options...
pauln Posted February 27, 2011 Share Posted February 27, 2011 One thing that will kill a rectifier tube is too fast a power cycle - turning off followed by immediate turning on. I don't know the specific physics; not sure if it is the rectifier, capacitors, or both; but there is a very fragile state for a few seconds after power off, and a subsequent immediate return to power catches that state in a potentially weak or unprepared condition. This has happened to people who in the course of doing something (tube rolling, changing connections, or just changing their minds) where they turn off and then immediatley back on. This also might happen if you experience a momentary power loss. Quote Link to comment Share on other sites More sharing options...
JBryan Posted February 27, 2011 Author Share Posted February 27, 2011 Thanks guys. There wasn't anything out of the ordinary that day. I just pulled the switch to listen to the radio - the same as I had done practically every day for the last 10 years and the 5AR4 suddenly filled with a blue/red/purple flash. I'll pop the hood and take a look but I guess its time for a restoration. Any suggestions for modifications - which caps sound best and should I make the switch from 7189's to EL-84's? What other mods have folks implemented to make the 222c sing? Thanks again! Quote Link to comment Share on other sites More sharing options...
jtnfoley Posted February 27, 2011 Share Posted February 27, 2011 Check the tube audio forum at audiokarma... There's a LOT of expertise floating around, and a lot of DIY info if you are so inclined. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.