Hi all,
I serviced my el84 amp over the weekend. It wasnt pretty, 1 cap on the verge of failure, 3 bulging but may have been fine for another year or so, and 1 suspect (but meaured fine, just looked a bit cooked) resistor. Its a baby huey type circuit, the balance of anode voltages on the signal tubes was also now way out.
Thats a 10 year old amp.
Out of pure interest, whats the typcial servicing intervals you stick to? what do the commerical producers recommend?
cheers
I serviced my el84 amp over the weekend. It wasnt pretty, 1 cap on the verge of failure, 3 bulging but may have been fine for another year or so, and 1 suspect (but meaured fine, just looked a bit cooked) resistor. Its a baby huey type circuit, the balance of anode voltages on the signal tubes was also now way out.
Thats a 10 year old amp.
Out of pure interest, whats the typcial servicing intervals you stick to? what do the commerical producers recommend?
cheers
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I usually bias my tube amps ever ~4 months or so. Beyond that, I don't mess with them unless I notice an issue.
I always buy name-brand caps from Digikey, and I usually buy caps rated for at least 5000 hours, preferably at 105C. I then try to position them away from heat sources when I can.
In general, with the exceptions of tubes, if it's too hot to hold a finger on for more than a few seconds, it's too hot.
I always buy name-brand caps from Digikey, and I usually buy caps rated for at least 5000 hours, preferably at 105C. I then try to position them away from heat sources when I can.
In general, with the exceptions of tubes, if it's too hot to hold a finger on for more than a few seconds, it's too hot.
When I started, I was using cheap and surplus components, and am paying the price now. Cheap caps fail.. Starting w/ old caps isn't a good idea, apparently.. Now I use non-electrolytic everywhere possible, and it's much more possible now than it was 10+ years ago. Even for PSU filtering, etc..
I'm surprised by how well things perform in the presence of failed caps and other issues. I had a failed screen regulator, just passing its input voltage to the screens. Didn't notice any problems before I tested it.
I've been checking the bias about yearly, and check voltages and visual inspection at that time...
I'm surprised by how well things perform in the presence of failed caps and other issues. I had a failed screen regulator, just passing its input voltage to the screens. Didn't notice any problems before I tested it.
I've been checking the bias about yearly, and check voltages and visual inspection at that time...
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Old Mrs. Humphrey enjoyed her 1962 console stereo right up to the day she died at 87, in 1998.
And guess what?
She never had to be bothered with that tedious messy job of having to yank the guts from her console for any sort of maintenance....
Ole old woman had a strong resistance to being paranoid of things, but she lived a very happy life.
And guess what?
She never had to be bothered with that tedious messy job of having to yank the guts from her console for any sort of maintenance....
Ole old woman had a strong resistance to being paranoid of things, but she lived a very happy life.
That old amp granny had was with very high quality components... relatively speaking.
She didn't have the plague of bad batches of electrolyte being put in poorly manufactured caps w/ no quality control.. That's what those of us building w/ inexpensive components in the 90's and early 2k's had... we're not making it up. They are failing.
She didn't have the plague of bad batches of electrolyte being put in poorly manufactured caps w/ no quality control.. That's what those of us building w/ inexpensive components in the 90's and early 2k's had... we're not making it up. They are failing.
I still have hundreds of Panasonic caps from the 1990s that I use all the time. Still new in the package. There's obviously a chance that they'll fail early, but they've been stored in a climate controlled building since they were new. It's a risk I'm willing to take, and perhaps I'll come to regret it.
Of course, it's best to avoid positioning capacitors where they're going to get cooked.
Of course, it's best to avoid positioning capacitors where they're going to get cooked.
1962 to 1998 corresponds to 36 years. Old, but I still see plenty of mid-80s gear that hasn't been recapped.
There are PLENTY of PA amplifiers that have been running since the mid 90s with minimal service with the exception of fan replacement. My MC450 ran continuously from 1998 to 2015 (and countless shows). I replaced the fans, but it still has its original filter caps. I haven't seen too many MC450s or 650s with faulty caps. Why? They don't run very hot. They were intelligently designed, and even though they are biased very hot, that heat stays AWAY from the power supply.
I see a lot of amp builds around here where people place caps far too close to heat sources. If you can't avoid doing so, at the very least use 105C caps, but you may even consider the use of 125C caps if you have to put a cap right next to a tube.
In my tube amp restorations, if at all possible, I put the filter caps under the chassis, away from tube heat.
I also consider mounting in respectable places away from heat in other (SS) amps.
Ventilation is also considered and if possible, enhanced.
OEM designers sometimes had no common sense, or shortcutted things.
I know everyone likes to flex their build muscles and say how greatly they design to avoid issues. But again... Not making this up. Not the fault of the design or the build. We got sold bad caps.
Capacitor plague - Wikipedia
Ask Hackaday: Experiences With Capacitor Failure | Hackaday
(I should mention my experience w/ this is actually from musical instruments, modular synths, etc... Things with hundreds and hundreds of caps. It is a very real problem. )
Capacitor plague - Wikipedia
Ask Hackaday: Experiences With Capacitor Failure | Hackaday
(I should mention my experience w/ this is actually from musical instruments, modular synths, etc... Things with hundreds and hundreds of caps. It is a very real problem. )
Update: it WAS a real problem.
That "bad caps" issue was in reality true, but to bring you up to date, is no longer troublesome.
By now, the majority of those products with bad caps have been diagnosed, mostly starting in 2002 and up to 2015.
However, in order to prevent future failure of new designs, installing capacitors from reputable sources/manufacturers is the thing to do.
Not buying stuff off of ebay vendors is smart.
Spend the time and aquire good caps from places like Mouser, Digikey, etc.
It would probably be best to simply not reply, but... It's still an issue! You don't need to bring anyone 'up to date', I'm in the industry. If things were powered 24/7 like business computers and monitors, the issue presented itself more quickly. But I still get things on my bench all the time which have these bad caps in them.
Like my original post says, I used these caps 20 years ago, and am just now having them fail in some of the things I built. I don't make **** up.
The OP is talking about a 10 year old amp, which if he got inexpensive caps, would have been exactly the time to get surplus bad electrolyte caps. I'm not saying that's definitely his issue. Just that yeah.. He's not alone in seeing caps fail and it may not be wise to simply assume he's a bad designer or builder.
Like my original post says, I used these caps 20 years ago, and am just now having them fail in some of the things I built. I don't make **** up.
The OP is talking about a 10 year old amp, which if he got inexpensive caps, would have been exactly the time to get surplus bad electrolyte caps. I'm not saying that's definitely his issue. Just that yeah.. He's not alone in seeing caps fail and it may not be wise to simply assume he's a bad designer or builder.
There is no servicing industry anymore for mainstream consumer electronics. It is not useful to design the product with capacitors that will outlast other less reliable parts such as non replaceable batteries and non volatile memories with limited write cycle life. Yes, capacitor manufacturers have mostly solved the issues, but the newfangled reliability has been already consumed by the drive toward smaller and cheaper designs. Today the capacitors have very slim margins and are placed near hot parts. The failure trend I see on newer products is not the bulging and leaking capacitor plague of the past, but rather the (tiny) capacitors increase ESR dramatically and reduce capacitance, with no exteriors signs.
No need for the harshness in reply there.
I've been in the consumer sales AND service business for 4 decades now, and I also don't talk out of my *** either.
We have a saying here in farm land, “It’s not the heat, it’s the humidity.” 
Without air conditioning moisture gets into everything. Contacts like tube pins and switches stop conducting.
“Achieving both flame retardancy and humidity resistance is difficult, because a side effect of adding flame retardants to resin is a decrease in humidity resistance. Lower humidity resistance allows moisture to enter the capacitor, which in turn can shorten the capacitor’s lifespan.”
https://www.mc.showadenko.com/english/report/061/61_tr09.pdf Hitachi design department
Without air conditioning moisture gets into everything. Contacts like tube pins and switches stop conducting. “Achieving both flame retardancy and humidity resistance is difficult, because a side effect of adding flame retardants to resin is a decrease in humidity resistance. Lower humidity resistance allows moisture to enter the capacitor, which in turn can shorten the capacitor’s lifespan.”
https://www.mc.showadenko.com/english/report/061/61_tr09.pdf Hitachi design department