I just experienced a strange thing and thought I'd post it here for others to check out. That gave me the idea of having a thread going for simply posting any useful experiences and thoughts about valves in general.
Ok, my own issue. My amp had a couple of days of sounding a little ropey. Despite calling them up via MIDI, it was difficult to get the sound out of it I was used to at home at lower powers. Somehow it just seemed flat and lifeless. I began to wonder if the valves were getting a little rough, despite them being only a year or so old. They are the usual quad matched JJ EL84s. Then I turned it on, it came up, but played with an occasional popping sound. It wasn't happening often, just now and again. The usual advice is of course "valves going, replace asap". That's too hasty a solution for me but something definitely had to be done.
I did the obvious things and checked out the bias with the magic pick. I was astonished. 2 valves were on 6 flashes, 1 was on 10 and the other on 24! And the two which matched weren't in the same pair. Then I noticed that when it was turned on it occasionally would set up with the outer pair being marked as faulty and switched off, but sometimes it was fine. A duff outer valve I thought and resigned myself to having to buy a new set. But then I got more picky.
I decided to simply swap the outer pair for the inner with the thinking that, as I use 18W or below most of the time, the outer pair would hardly have been used. The outrageous bias reading was given on one of those outers but I figured it would be interesting to try it. Two minutes later and I had them swapped. I lit it up, the usual scary light show from the heaters which I find with JJs, and Bob was my mother's brother, it worked perfectly. No bias issues, a recheck showed them all now within 3 flashes, and the sound was back to magnificent. It has had days of home use and a full fledged afternoon's rehearsal and not a peep. It behaved better than for months.
Now I figure the solution is probably the obvious. Removing and replacing them most likely simply cleaned the pins of tarnishing. It had never occurred to me that slightly tarnished contacts could be so invasive without actually preventing the amp from working. My plan now is to remove them every month or two and clean all the pins with a "proprietary fluid". I also have a tube of special contact grease I use for other types of circuitry, not a cleaning agent but one to lubricate switch surfaces, prevent tarnishing and promote good long term contact. This is really good stuff, but for use on valves I am waiting for advice from the manufacturer as to its suitability for high voltage circuitry like ours.
One thing I am curious about is that I use my own home made plinth with forced ventilation for additional cooling. It is just a wooden base with 4 computer fans fitted in. The amp bottom sits with its bottom vents surrounded by a sealing strip and the fans force air into the base and up out of the top. It makes a really big difference to the case temperature so seems to be working on the innards. However, this air will use every path to find its way up into the top section and one of those paths will be up the valve base contacts. I was curious as to whether the airstream was accelerating corrosion in some way. High voltage parts do have their own ways of degrading exposed contacts. Old tube CRT type TVs used to grow notorious "black jam" on their tube's rear pins which was a thick grease like gunk which eventually built up enough to short out the contacts.
So, anyway, a horror story averted, I didn't need to put more money into the bottomless pit of "music for fun". Anyone else out there with an amp which is sluggish or misbehaving like mine could do well to simply remove the valves, clean the pins and replace them. It's the cheapest valve repair you will ever do. They really are much more reliable and long lasting than they are given credit for. (So many myths for us to debunk!!!! )
Ok, my own issue. My amp had a couple of days of sounding a little ropey. Despite calling them up via MIDI, it was difficult to get the sound out of it I was used to at home at lower powers. Somehow it just seemed flat and lifeless. I began to wonder if the valves were getting a little rough, despite them being only a year or so old. They are the usual quad matched JJ EL84s. Then I turned it on, it came up, but played with an occasional popping sound. It wasn't happening often, just now and again. The usual advice is of course "valves going, replace asap". That's too hasty a solution for me but something definitely had to be done.
I did the obvious things and checked out the bias with the magic pick. I was astonished. 2 valves were on 6 flashes, 1 was on 10 and the other on 24! And the two which matched weren't in the same pair. Then I noticed that when it was turned on it occasionally would set up with the outer pair being marked as faulty and switched off, but sometimes it was fine. A duff outer valve I thought and resigned myself to having to buy a new set. But then I got more picky.
I decided to simply swap the outer pair for the inner with the thinking that, as I use 18W or below most of the time, the outer pair would hardly have been used. The outrageous bias reading was given on one of those outers but I figured it would be interesting to try it. Two minutes later and I had them swapped. I lit it up, the usual scary light show from the heaters which I find with JJs, and Bob was my mother's brother, it worked perfectly. No bias issues, a recheck showed them all now within 3 flashes, and the sound was back to magnificent. It has had days of home use and a full fledged afternoon's rehearsal and not a peep. It behaved better than for months.
Now I figure the solution is probably the obvious. Removing and replacing them most likely simply cleaned the pins of tarnishing. It had never occurred to me that slightly tarnished contacts could be so invasive without actually preventing the amp from working. My plan now is to remove them every month or two and clean all the pins with a "proprietary fluid". I also have a tube of special contact grease I use for other types of circuitry, not a cleaning agent but one to lubricate switch surfaces, prevent tarnishing and promote good long term contact. This is really good stuff, but for use on valves I am waiting for advice from the manufacturer as to its suitability for high voltage circuitry like ours.
One thing I am curious about is that I use my own home made plinth with forced ventilation for additional cooling. It is just a wooden base with 4 computer fans fitted in. The amp bottom sits with its bottom vents surrounded by a sealing strip and the fans force air into the base and up out of the top. It makes a really big difference to the case temperature so seems to be working on the innards. However, this air will use every path to find its way up into the top section and one of those paths will be up the valve base contacts. I was curious as to whether the airstream was accelerating corrosion in some way. High voltage parts do have their own ways of degrading exposed contacts. Old tube CRT type TVs used to grow notorious "black jam" on their tube's rear pins which was a thick grease like gunk which eventually built up enough to short out the contacts.
So, anyway, a horror story averted, I didn't need to put more money into the bottomless pit of "music for fun". Anyone else out there with an amp which is sluggish or misbehaving like mine could do well to simply remove the valves, clean the pins and replace them. It's the cheapest valve repair you will ever do. They really are much more reliable and long lasting than they are given credit for. (So many myths for us to debunk!!!! )