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Hi,I have some Vitamin Qs that have solid metal on one end and epoxy on the other. Is there any directionality to these, or is this simply a can/case made for easier production (i.e., fill it up and then seal it with epoxy)? Thanks.
Follow Ups:
Do you mean that one lead is touching the metal case?If so, you want to tape those so they don't short. If you are using them for coupling caps, connect the case end to the point in the circuit closest to ground. Most of the time that will be the plate of the driving stage.
Example; a 6sn7 stage will have a output impedance of around 7.7K while the grid of the next stage is 100K.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hi Tre,It's an axial capacitor, with leads coming out of both ends of the case, one end is metal and the other is epoxy. Here's pictures of both ends - found an old eBay listing that looks like the same thing:
Thanks!
Put a meter on it and see if the metal end is connected to the case. Either way use the metal end as the outside foil. (side connected closest to ground)Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thanks a million, Tre! Greatly appreciated.
You should connect the outer case leaded connection to the grid connection, not the plate connection. That would be the lowest positive voltage, closest to ground, thus the safest way, and the way the manufacturer intended.
For PIO caps that are not connected to the case, they are presumed non-polarized. However, a number of us techies always connect these in the direction of the labelling, with the labelling heading toward the next stage, the grid connection.
All NOS caps have significant break-in hours needed, before you sonically critique them. Happy Listening on your hifi search...
Just to double-check on this - I'm coupling a 12AT7 plate to an EL84 grid, so the outer foil, or the metal end of the case, should point toward the EL84 grid, correct? Many thanks.
IT, you are right. PIO caps are non-polarized. A reason to hook them one way or the other has to do with noise pickup. Most guys will hook up the outer foil to the connection that is closest to ground. Not in terms of voltage but of impedance. That would be the plate in most cases, so that the cap picks up the least amount of noise.Sometimes it's hard to know which end is connected to the outer foil. A tone generator and a scope can help.
Some of the old VitQ caps do have one end connected to the outer metal case. These don't seem to be but looking at the pictures it does look like the end showing metal would be the outer foil side. (that is, the outer foil that, in this case, is inside the metal case)
Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre, The grids are closer to ground than the plates. Even though you might strive for power supplies with low impedance, the grids should be, and usually are, closer to ground. If yours are not, then maybe you should be designing circuits with lower resistance grid circuits, or using lower impedance transformers, loading the grids. The high voltage power supply is isolated from ground by high impedance, high voltage storage caps.
Especially with low mu triodes, the grids should be closer to Earth/Ground. Also, the designers of the caps did not expect you to, or want you to, get high voltage shocks. The so-called outer foil, and cap case, is to be connected to the negative end of the capacitor's circuit.
Many of the polarized caps, with one lead actually being connected to the case, were meant to be bypass caps, not coupling caps. However, many of these sure do sound great as coupling caps.
"Tre, The grids are closer to ground than the plates. Even though you might strive for power supplies with low impedance, the grids should be, and usually are, closer to ground"How is that true? If you had a grid choke, the grid would be closer to ground in terms of DC but we are concerned with AC. A good grid choke will have a very large AC impedance.
Example; a 12ax7 with a 180K plate resistor running 1ma. with 120vdc on the plate. The z-out of that stage is 38K. The Z of the following stage grid circuit will be the value of the resistor (220K or better so the 12ax7 is not loaded down) or the AC impedance of the choke. So I don't understand what you are saying. Sorry.
"Many of the polarized caps, with one lead actually being connected to the case, were meant to be bypass caps, not coupling caps. However, many of these sure do sound great as coupling caps. "
I agree and use some of that type as coupling caps. I just wrap them real good with tape so they don't short to anything.
Tre'
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hi Tre',
Let us see if we can help the understanding. I do not wish to argue this at all. It is common knowledge that the Outside Foil was designed as the negative lead. While many manufacturers have also neglected this fact, using the line coded, outside foil cap end as the positive lead, the cap designers meant the outside foil as the negative lead. If you read some very early tech lit, you will soon agree. All electrolytic (and positive) power supply caps always have their outside foil/case end grounded or close to ground;(except negative voltage supplies, of course).
AC Impedance is paperwork, theoretical, guidance info, frequency dependent mathematics. When you discover that lower impedance(than the tube manuals indicate) grids sound better, what theory will be made up; and does the theory matter, when the practical application decides for us ? Practical engineering inspires theory.
When the books tell us that current flows from one polarity to another, how does that help us stay safe ? Practically, it does not help us, at all. It would be simpler and better that the book simply said: Don't get in the way of that current, or, don't be the conductor of that current. Now, that would help us stay safe, right ?
But, no, the books after WWII get more and more technical, leaving behind the practical info, so prevalent in 1920s and 1930s lit.
From your example above, with the lowish Rg, I see that you realize that low grid impedance is a good thing, even though most manuals specify that Rg should be at least 2 x preceding Rp.
There is a thread going on, right now, that is related to our practical thinking, concerning design points for tubes. It is interesting how many folks try and declare which is technically better, when it is the end result, the sound, that matters. I know that you agree with me about this, for certain. While tried and true circuitry is great, deviating from the norm, sure can change our sonic results. Happy Listening ans Safe Experimenting ....
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