SWL Posted October 7, 2018 Share Posted October 7, 2018 My 222c was restored by Stereo Rehab last year. It's been rock solid. No issues and sounds great. Since then I've been using the 7189 Preferred Tubes from The Tube Store with zero issues. Recently, I overhauled my room's acoustic treatments and the biggest surprise was how much better my 222c sounds now. So I'm buying some more quads of power tubes because I plan on using this amp more often. Got a quad of some Siemens EL84/6BQ5 tubes yesterday and they sounded great until this morning when one of them red plated on me. Quite the experience since this has never happened to me before. So I took the Siemens tubes out and put the original tubes I has back in there...the 7189 Preferred Tubes that I've never had a problem with....and I couldn't get them to bias anywhere near where they were supposed to be.....and they got REALLY hot. So I took out the 7189 Preferred Tubes and put in another quad of some Russian tubes. I can't remember the number off hand but they are gold grid, military tubes blah blah blah I'll have to check but they biased fine, sound fine (really good actually) and there doesn't seem to be any issues so far after about about an hour of listening. Any ideas on what could've happened here? I really appreciate any input. Thanks Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 7, 2018 Share Posted October 7, 2018 Do the tubes seem to have a good bit a tension putting them in and pulling them out of the tube sockets? You may have intermittent tube pin contact going on. If the control grid doesn't achieve good contact the tube will run away cherry red. I take the amplifier was modified to allow you to test tha adjust the bias since the original 222C only came with balance controls and no provision for testing the bias. Quote Link to comment Share on other sites More sharing options...
SWL Posted October 7, 2018 Author Share Posted October 7, 2018 I'd say the tension on the pins is just right.....and yes, the unit was modded for the bias.I went back a few hours later to check the bias on the Russian tubes and they were all out of whack. Put the 7189 Preferred Tubes back in and although they sounded awesome, the bias was again completely out of whack. Again, before I changed these power tubes there were no problems whatsoever with the bias on the 7189 Preferred Tubes. Since the restoration the unit has been 100% problem free.So if I did in fact did not put the proper power tubes in the 222c and one of them red plated, could there be damage to the amp? I think I'm gonna be sick.Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted October 7, 2018 Share Posted October 7, 2018 There is always a concern with a tube red plating. This could be a faulty tube or something in the biasing chain including the amp. Get rid of the tube that seem to be the start of all the trouble and have a tech checkout the amp. Quote Link to comment Share on other sites More sharing options...
joshnich Posted October 7, 2018 Share Posted October 7, 2018 What does stereo rehab have to say? In this kind of situation I would always check with who did he restoration. I’m assuming they have some kind of warranty. Quote Link to comment Share on other sites More sharing options...
SWL Posted October 8, 2018 Author Share Posted October 8, 2018 Like I said in the OP, I've had this amp for a year now since the restoration and it has been amazing and 100% trouble free.The problem came yesterday when I put the wrong tube in it. It's been a few years since I started learning about this stuff. I got away from tubes for a while and forgot a couple of things......like the Siemens EL84/6BQ5 I put in there wasn't robust enough for the 222c plate voltage. The power tubes should be either 7189's or if they are EL84's I think they have to be an 'M' version.This was totally my fault out of haste. I will be getting it to my tech to check out after he's back from vacation and don't want to bother him until then. In the meantime I'm really bummed because man did it sound good with those Siemens tubes and now the amp may or not be damaged due to my neglect. Casper at Stereo Rehab has been a fricken wizard with all my gear and I trust/recommend him 100%. In the meantime my restored Marantz gear from him is getting me by just fine.....but man, that 222c is something special.Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted October 8, 2018 Share Posted October 8, 2018 One of the amp resistors may have fail with the tube working beyond it capacity. Just don't keep trying to use the amp or test other tubes. No bad smell so the transformer most likely is OK. Transformer are an expensive part of an amp repair. Quote Link to comment Share on other sites More sharing options...
SWL Posted October 8, 2018 Author Share Posted October 8, 2018 Yeah, no bad smell just a very bright tube and the bias issue.Sent from my SM-G950U using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
Schu Posted October 8, 2018 Share Posted October 8, 2018 A bad resistor was the part in one of my amps that caused a run away situation. Thankfully the builder is awesome and helped diagnosis and repair the situation before something really bad happened. Lack of ability to bias was the key. 2 Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 9, 2018 Share Posted October 9, 2018 What do you mean by "you put the wrong tubes in it" ? I'd suggest taking it into your technician something is bad and it is almost surely what caused the tube to red plate in the first place. It happens and probably will be a easy fix. If the filter can directly in front of the power transformer is original I suspect that will have something to do with it. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 9, 2018 Share Posted October 9, 2018 Ahh okay I just reread your first post.. those vintage Siemen EL84's should have been fine in there...if they were good to start with. The only real problem with running regular EL84's in the amplifier designed for 7189's is they will not last long, they generally run just fine and sound really good. They just don't last as long. Vintage EL84's hold up better to this abuse then most modern productions. Thing is in my opinion those Russian surplus tubes (preferred series) and the current Sovtek EL84M (same basic tube) sound really good and last like any 7189 ever made. PS: one of the reasons those EL84's sound so good IMHO is you're running the dog shite out of them! 2 Quote Link to comment Share on other sites More sharing options...
SWL Posted October 10, 2018 Author Share Posted October 10, 2018 What do you mean by "you put the wrong tubes in it" ? I'd suggest taking it into your technician something is bad and it is almost surely what caused the tube to red plate in the first place. It happens and probably will be a easy fix. If the filter can directly in front of the power transformer is original I suspect that will have something to do with it. I'm praying that it's an easy fix!Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
SWL Posted October 10, 2018 Author Share Posted October 10, 2018 PS: one of the reasons those EL84's sound so good IMHO is you're running the dog shite out of them! Man, I'm telling you since taking the time to dial in my room's acoustics and almost burning my house down with those tubes it WAS....tube bliss. Now I just wanna shoot myself for putting those tubes in there because before there was no problem with the bias. It was rock solid.Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
SWL Posted October 14, 2018 Author Share Posted October 14, 2018 Ok, it's been a week now since this happened and I've gotten so impatient to the point that I've gone against some of the common sense suggestions. I retraced the timeline of the redplating event and everything I tried with two other quads of power tubes besides the quad that red plated were all done while the amp was still pretty warm on the verge of being semi-hot. The amp sounded and performed fine but the bias was all over the place. Fast forward a week to yesterday, I fired up the amp.....7189's in the amp.....set the bias after about 15 minutes.....everything was cool. Not out of whack but normal like it had been before the redplating incident. Played the amp for about four hours closely monitoring it only leaving the room to take a leak. Using my hand to check the temp of the amp everything seemed normal. Sounded great. Nothing abnormal happened.. This morning I've been listening for about three hours. Temp is good. The bias drifted a little since yesterday so I reset it and so far so good. I'll keep my paws off the bias for the rest of the day and see what happens and won't play the amp if I'm not around. I'm definitely planning on my tech looking at it asap. In the meantime everything seems cool. What do you guys think? Did the amp just need some time to cool down? I think I caught the redplating tube right away....I hope. I just don't know how long it was redplating before I heard the noise in the right speaker and then shut it down. Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 16, 2018 Share Posted October 16, 2018 Well honestly I wonder if this is user error. Not sure how they setup your biasing scheme but if they kept the balance controls and added voltage controls like I do to a 222C I've had a few folks get confused and mess up the bias. Reason I suspect user error is things like this don't generally fix themselves in my experience. 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted October 17, 2018 Share Posted October 17, 2018 This stuff can be dangerous and working right for one or two day is no guaranteed. Be careful, except I don't know how to tell you to do it. 1 Quote Link to comment Share on other sites More sharing options...
muel Posted October 17, 2018 Share Posted October 17, 2018 I think also you need to be more specific than "bias is out of whack" and "all over the place." You probably know it varies as it warms up and you don't check while playing music through it. A 15 minute warm up isn't warmed up quite yet in my experience. 30 minutes later I could almost promise it will measure different I wouldn't leave it unattended while turned on. 1 Quote Link to comment Share on other sites More sharing options...
SWL Posted October 20, 2018 Author Share Posted October 20, 2018 Thanks guys.....sorry for the late reply but I've been real busy at work.Just flicked on the tunes for the first time since last Sunday. I parked the 222c until I can get it looked at."User error"? Sure. I'm no tube amp expert by any means. This is how it all went down. Got the amp restored a little under a year ago. Since then it has been perfect in every way. No problems whatsoever. I'm fully aware that the bias is gonna fluctuate. Their wasn't a problem UNTIL I put the EL84 tubes in there.....and then one of them redplated. Immediately after the redplating, I took the EL84's out of the amp and tried two other quads of tubes that I was using previously with no issues. What I meant by the bias being out of whack and all over the place, was that it was very erratic and I was unable to get it into the proper range. The amp was still very warm, sounded fine but the bias was nowhere close to being stable......and of course it's going to fluctuate a certain amount but this was to the extreme.A week went by and I fired the amp back up with the 7189 Preferred Tubes I had in there originally after the restoration that were problem free. I played the amp virtually all day on Sunday. I was a vegetable from working a 70 hour week. I closely monitored the amp constantly checking the temp by hand making sure it wasn't getting too hot. I checked the bias three times throughout the day. It was showing normal fluctuation that I've observed in the past. Nothing to be concerned about in my mind. So as far as user error, I don't know what I could have done wrong besides putting those EL84's in there. Apparently, it was a bad tube and even though they aren't quite capable of handing the plate voltage over a long period of time.....it shouldn't have redplated in the first five hours of operation unless the tube was bad for other reasons....correct?So now I'm wondering since I last played the amp for a whole day straight without any obvious problems.....was the whole redplating incident a hiccup that was disrupting the bias and the amp just needed some cool down time? Is this just wishful thinking on my part?I WILL take it to my tech. Problem is that he's slammed right now. In the meantime just trying to see what you guys think. Thanks for all the input so far.Sent from my SM-G950U using Tapatalk Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 21, 2018 Share Posted October 21, 2018 Well realize I'm to some degree guessing so don't take my comments as written in stone. It's pretty much impossible to consistently diagnose these problem over a forum. Most of my guessing that led me to say user error is amps that are red plating don't sit for a day or two then just stop red plating. These types of things don't magically fix themselves. The only thing that comes to mind that could make this intermittent would be tube pin to tube socket connection problems (as is loose dirty sockets). I'd be watching it close until the problem gets tracked down for sure. 1 Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 21, 2018 Share Posted October 21, 2018 Oh and as to what I meant by user error. Its pretty easy to screw up the biasing if the amps has a control per channel to balance the pairs of tubes and the technician added a control feeding each balance control to raise and lower both tubes in the channel at once. Here how the error would happen. I'm assuming the bias scheme was setup keeping the factory bias balance controls in the circuit. You insert both probes in the test points for the channel to be balanced and set the balance control so your meter reads 0 VDC (zero equates to both tube being the same), Then you pull the black probe out place it on the bare chassis for ground and check the bias voltage (here is where the mistake comes in) mistakenly you adjust the balance control instead of the new bias voltage control to lower the tube the red probe is inserted in. The balance control can lower one tube but in doing so raises the bias of the other tube in the channel. If this is allow to run for a few hours that tube that is mistakenly biased high can decide to red plate from long term over bias condition. 1 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.