Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: spacelabstudio on July 11, 2011, 02:43:58 pm
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When it comes to new, off the shelf electronic components, pretty much the only components that die on me with any regularity seem to be silver mica caps. If somebody's dumping high voltage on a tone pot, it's a silver mica cap. I dunno. I have A/Bed to cheapo ceramic disk caps in certain applications and while I can hear a difference, I'm not sure I care that much about a little extra graininess in a guitar amp. Anybody else have this experience?
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Yup.More times than I care to mention.I avoid silver mica when possible.
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So.. what does that leave ? Ceramic ?
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yes,and they work just fine.
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The ceramics are certainly less expensive. I have a hard time discerning their voltage ratings when they don't say "1kv" for example. Do you ever use silver micah's any more physcho?
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I do but I am very aware of when they start to leak.The tone is very marginally different,so close that if I can get good ceramics I just don't bother with silver mica.
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What do you consider to be good ceramics ?
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These are pretty good 5% tolerance 1kv
http://www.mouser.com/ProductDetail/Xicon/140-102S6-471J-RC/?qs=sGAEpiMZZMukHu%252bjC5l7YcAYJsB7D8DI5XlHbikRdXY%3d (http://www.mouser.com/ProductDetail/Xicon/140-102S6-471J-RC/?qs=sGAEpiMZZMukHu%252bjC5l7YcAYJsB7D8DI5XlHbikRdXY%3d)
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I've had silver mica caps fail on me, much to my surprise.
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If you are using silver micas in a tone stack and they are failing, you can stick a film .1uf in front of the whole tone stack. This won't affect the performance of the stack at all, yet will allow the silver mica to keep on chugging since it doesn't have the DC on it anymore.
Greg
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It seems to me that silver mica caps are more sensitive to heat than any other component (except solid state doo dahs). Do you all always use heat sinks when soldering silver micas?
Just wondering,
Chip
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Had my share of Silver Mica's go bad right out of the box.
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I've never used a heat sink to solder. I haven't stumbled across any info recommending that. Maybe that's part of the problem. I don't know. It has occurred to me that I'm pretty sure I've never run across silver mica caps in commercial equipment. Maybe it's not just because of the cost.
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I don't have much experience with consumer grade silver mica or guitar amp repair except for the few amps I've built or restored. However, I've been working with high quality mil spec equipment that's loaded with silver micas for 40 years. I've never ever replaced a silver mica cap.
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I feel lucky then since I've not had any go bad on me. But I like to solder hot and quickly - get on & get off. I rarely use heat sinks even on SS stuff and rarely if ever can I recall any issues there either.
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The thing about PC board stuff is the board itself acts like a heat sink.The pad effectively stops heat from traveling up the wire of the component.Within reason of course.
some Silver Mica stuff we get across the counter must be pretty crappy quality wise.I've built many,many amps with zero failures but recently I've done a few Ceriatone repairs where the silver mica caps were leaky.Asian silver mica?
When I source my own I don't seem to have problems.Famous last words.
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i try to buy quality caps, e.g. CD, Vishay. never had a problem w/ silver mica yet from either supplier. silver does not like a lot of heat. be careful w/ reflow time and temps.
ceramics tend to be microphonic. i don't like them in tone networks. i'll use them in PS and high voltage decoupling.
use polystyrene as an alternative - they are available in the picofarad ranges we usually use in audio, they are stable, high voltage, and usually less microphonic than ceramics.
BTW, be careful w/ SM and ceramic radial lead caps - if you crack the coating off the leads up into the body, moisture can seep into the dielectric. bend the leads below the ceramic if you have to mount them axially.
--DL
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BTW, be careful w/ SM and ceramic radial lead caps - if you crack the coating off the leads up into the body, moisture can seep into the dielectric. bend the leads below the ceramic if you have to mount them axially.
I always use sm needle nose for bending cap leads on everything not axial, just good form I guess? I knew it wasn't good to crack the material at the leads but didn't exactly think as to why. Thanks DL
I've yet to buy me some polystyrene high voltage caps for tube amps but in my SS amp & pedal days of yore I used a lot of polystyrene types especially in high gain loops. Those little thin wires and plastic grey bodies were very easily broken or melted. Not the sturdiest things in the world but they sounded great and were very stable.
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I don't know , the SM caps I've used seem to be fine. While on ths subject of caps just for the h--l of it I removed just the pot wire ends of the tone caps in a BF tone stack , I had malloy 150's and a 250pf SM and then changed the malloy's to xicon , didn't hear a change at all . today after removing the tone pot leads and then jumpering the malloy 150's in their place and a ceramic 250pf cap which was the easiest why I could think of rather than removing the caps from the eyelet board . I still did not hear a bit of a difference . Yet I read all over sites saying this type of cap cuts more highs and this one is brighter than that one. Also read that the simpler the amps circuit is the more this difference is heard . It was easy to un-clip the malloy's and jumper in the xicons and SM back in I just added alligator clips to the ends of the un- soldered tone pot leads . I just had a chop stick there to clip the clips to and keep them from touching anything .
Maybe it's me but nothing stood out to me at all . I got much more change removing the JJ 12ax7 and plugging in a sovtek 12ax7.
I read and do believe that all componants make up the amp even the quailty of the PT and the OT and of course the speaker and tubes. I have read this on this forum as well.
Fender used all sorts and brands of caps through the years . I had three different champs a 68,80 and 73 all had different brands of caps and all if memory serves used a ceramic cap as a coupling cap I know the 73 did and big Dk blue bass pot caps the .1uf and .047. They were like orange drops in style and size no name on them .
I use heat sinks , mainly to hold the leads of a resister and cap and wire in place going into the same eyelet when changing a componant and even on a new build when the eyelet board is not installed and I get everything in place at the back of the board , solder then clip the ends. and who knows which componant will suck up most of the heat.
I had soldered without a heat sink too, even if you are in there and out in 2 seconds touch a resister and tell me it will ever get this hot under normal use. I use old very well made Ungar irons 44 watt element that screw in and a 1/8" wide chizzle tip .
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Old Silver-Mica was usually 500V rating.
I see that _NEW_ SM caps are often 50V rating.
In sizes below 1,000pFd, ceramic is very-very fine. Just check the voltage rating.... this is a 3.3V world so you don't get 500V parts without a struggle.
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"and then changed the malloy's to xicon , didn't hear a change at all ."
Sometimes the very slightest changes can be heard and sometimes not. It's purely subjective to who's doing the listening and in some cases it's a matter of what a person 'wants' to hear even though it may not even be there.
Our ears are very sensitive but our brain's interpretation for differences and the memory to remember the differences is very short. Then throw in people's descriptions for what they perceive and that's a whole 'nother can o-worms.
An example - I've had a hard time distinguishing speaker differences (which should be the easiest to distinguish and make the most difference to hear changes made to an amp) at times when plugging and unplugging them in but it wasn't until using an A/B box to literally switch on the fly that the differences were much more realized than that older manual way of changing them by hand one at a time. It wasn't until this that you really 'could' hear distinct differences and then you could also hear much more of subtle nuances in characteristics between when played very loud or moderate volumes, clean or overdriven, slow or fast, chords or single notes, etc...
You could start a whole new thread for this subject.
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Maybe we listen with our eyes? Plus if you spend $220+ on an Alnico speaker, the psychology involved with evaluating its sound may be, how do you say, possibly biased (no pun intended).
I'm guilty as anyone, but I picked up some Xicons & ceramics at my local wire shop & I'm willing to bet they will sound just fine.
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I worked on Navy Submarine gear for 24 years and never had a SM failure. Been building amps for the last 11 years and never had a failure. I have replaced many microphonic ceramic caps in amps. Maybe the lead bending process is causing the failures.
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"and then changed the malloy's to xicon , didn't hear a change at all ."
Sometimes the very slightest changes can be heard and sometimes not. It's purely subjective to who's doing the listening and in some cases it's a matter of what a person 'wants' to hear even though it may not even be there.
Our ears are very sensitive but our brain's interpretation for differences and the memory to remember the differences is very short. Then throw in people's descriptions for what they perceive and that's a whole 'nother can o-worms.
An example - I've had a hard time distinguishing speaker differences (which should be the easiest to distinguish and make the most difference to hear changes made to an amp) at times when plugging and unplugging them in but it wasn't until using an A/B box to literally switch on the fly that the differences were much more realized than that older manual way of changing them by hand one at a time. It wasn't until this that you really 'could' hear distinct differences and then you could also hear much more of subtle nuances in characteristics between when played very loud or moderate volumes, clean or overdriven, slow or fast, chords or single notes, etc...
You could start a whole new thread for this subject.
No thanks , no way am I starting a new topic on this one :w2: This may come as no surprise, I don't own a cap tester , wish I did , I just trust they are good , I can read if they pass dc but I have no way of knowing their actual reading
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All my amps were built with silver micas
Never had one go bad yet.
Some of my oldest amp builds are approaching 20 years old
Maybe it is chinese SM's now a days, hard to say.
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The only cap I've ever gotten bad brand new was a Sprague Orange Drop. I've never had a cap I've installed fail. Xicons, including SM's, have been bulletproof for me.
Dave
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Another thread on this topic:
http://www.el34world.com/Forum/index.php?topic=10654.0 (http://www.el34world.com/Forum/index.php?topic=10654.0)
/Leevi
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I've had no problems with the Cornell Dublier 500 volt ones at Mouser and
I soldered the crap out of them.There certainly is a big difference in the sound when used as a treble cap in the tone stack compared to anything else.
Another thing I tried was ERO Roederstein 220 or 470 pf 630v KP1838 PP film + foil capacitors.
They seem to work alright too.I think they still make something similar.