One of the intended purpose of the meeting , which for obvious reasons these meetings never goes as planned due to the random nature of DIY, was to shootout two headphone HP amplifiers over modded HD headphones. Output cap-coupled to a TVC to his main system when he uses it as preamp. Otherwise cap couple to HDs headphones. Sunday morning and my brain already started with a lot of activity early today.

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I have the original price list not a copy. Here you can see C3g has cost DM for one. That is Euro. The factory price for the standard 50pcs box was Euro. We have not reached this price level yet, but one day it will happen. All great tubes are now more expensive as when new made. Admitted, in the steel can they are not glowing so nice. Believe me, once you feel these tubes get warm, you start to see them as tubes also.

C3m inside C3g with cap. Well, I can! So they started to speak very loud into the phone, but that didn't help much. II remember people in the Hewlett Packard open office even would look important, by talking too loud, indicating they were on an expensive long distance call.

Those would really had a lot to say, would just speak for one two hours. That was another world as digital calling via the internet. But in those days, very probably those analog calls passed C3g, and C3m tubes from the German post : Anyway this is not what good signal transmission is about, but it was the limits of what was possible with ocean cables.

About Noise. Which two things come together, as if they are married. The reason for this is, a long distance telephone cable is a noise generator, and an attenuator at the same time.

So after a certain length, the noise gets more and signal gets less. This limits the length of a telephone line, and simply amplifying the low signal at the receiving end, would also amplify the noise. So once noise is introduced at low signal, you can't get rid of it any more. If this is unclear to you, imagine the following. On a loud market place in the open, somebody shouts a message to you from 20 meters distance.

You can understand it, regardless the noise. You could repeat the message, and shout it to the next person also on 20 meter distance. So you are a 'repeater', and with 20 repeaters, you can send a message over meter distance, regardless the high noise level. Without repeaters however, it would be impossible to send the initial message over meters with all that terrible noise. If they all would silence, it would be no problem, but in reality it is opposite. The larger the distance, the more people are in between, and the more noise you have.

So using repeaters is the only way. So low distortion is also imporstant, because when every repeater would add jusz a tiny bit of distortion, at the end a total mess would be received. Now suppose you don't want to use repeaters, this is simply NOT going to work. Indeed the only solution is, to repeat the message before it gets lost in the noise. You see, with a long distance voice transmission cable, all of this works just the same way.

So the only solution is, to re-amplify the signal before it gets too noisy. It increases the maximum length of a cable, by putting in repeaters, by amplifying the signal before the signal-to-noise-ratio SNR gets really bad.

Doing so, we can overcome distances from one continent to the other. Though practical situations are extremely difficult, and such projects are higher arts of project management. Imagine the weight of such a cable on a ship, or the trouble with tube repeaters in salt water, with a meters column of water pressure on it, inaccessible for ever, somewhere between Honolulu and Paris, on the ocean bottom.

You would want such tubes to WORK and not fail for silly reasons. Going further back to the 's, this had to be done with tube equipment. Of course they tried to use as little repeaters as possible. The ideal repeater amplifier adds no noise, has no distortion, draws no current, is very small, needs no maintenance, and works for as long as the cable lasts.

A partial solution you get from adding an auto transformer Pupin coils at certain distances, but there comes a moment where you need active amplification. So the engineers desired the 'ideal' tube. However, these ideal requirements do not go together well: High Amplification, low noise, long life, no distortion, small size, low filament power. As most of you know, a tube with more heater temperature will have better electrical performance, and more lifetime, but uses more power too.

So the solution is a bit more complicated than you might think. The price of C3g was DM for one tube. So a standard Pack of those had the price of two new cars. You really need to imagine that.

So obviously, cost was no issue with those, and that's logical since with those you could for instance work with a cable that had a bit higher loss, and add repeaters inside to compensate that. This is the world of C3g, C3m, C3o.

Sorry for this way of speaking, but I just wanted to bring my point, these tubes are not just any tubes. Today, I think most of the secrets of how to make C3-tubes are gone with the wind, but at least we can still buy those miracles of design art from new old stock. If the days come where we only can buy used ones, it's no problem too, since the end-of-life is clearly specified in the datasheets.

So you can always tell if the tubes are still good. I found the Funke W19 tester very reliable in picking out used tubes with good lifetime in it. Optional: Individual series number on each tube Let me bring to your attention, the C3g at it's introduction in was the fist Frame grid tube, and it was not available commercially.

In short, a frame grid means the grid wire is not self supporting, but is wound around a hard metal frame. Like this, they could use wire which is so exceptionally thin, as it was never possible before. You cannot see this wire with the bare eye. This is quite strange to observe, when you take a frame grid tube apart. The grid wire is there of course, and you can 'see' there is something there, that you can look through, but you cannot see what that is.

As if there is a gold colored, transparent layer, that you can see through. Things looks a bit 'unsharp' when you look though. Like the low resolution picture below. It is just like this when you look at a frame grid wit the bare eye. Then, if you click the picture it gets enlarged, and you can see the wires. This technology is more expensive, and was used for very few tube types, perhaps only. Given the 10's of thousands other tube types ever made, this is not much. NOTE that in the 's when tubes were obsoleted, there was a lifetime-buy option by Siemens for the German post.

It stretched over a few years. It is from this period that BIG lots of tubes were made, and just stored for later service of old hardware. Because of the high manufacturing numbers, these were very good quality.

Probably many other tubes as well, it's just these three Types I ran across myself. Something similar happened in the USA, and from that period many very good , , 12AT7 and are around. These are those tubes with a barcode label on them. Then, the whole hardware developed so quickly after the digital multiplexing was used, and analog repeaters were taken out of service everywhere sooner than expected.

And so, a six digit number of those tubes were stored and never used. Through the years these were sold, and it seems the German government stocks of C3g and C3m have dried up since or so.

However, these tubes are always somewhere, and find the path to their end user. Check for a 16 pages!! Just look at how nice the triode connected curves are. What to do, if you don't like the metal cap? You can take off the metal housing, and inside is a very nice glass tube!

Look at the two round plates above the pins. The lowest is a metal shield outside connected for lower hum. The other is the mica. The anodes are open from the sides. This open construction is the best for finest linearity. It allowed plate distance adjustments after the tube was assembled. So that is additional to the Barium getter ring or plate. A Zirconium getter is expensive and it works like this: A Barium getter has most of its function during the short moment a few seconds that it is flashed during production, so when it is in the tube in the form of a cloud, while being transferred out of the getter halo, and condensing on the tube glass.

This cloud, at the moment it exists inside the tube, absorbs at that short moment almost anything whatsoever. Then, after it will be condensed on the glass, the Barium getter is only conditional active.

Like during great heat such as with KT88 tubes. However, little tubes like C3g cannot really use the getter anymore after activation. Of course there are some remaining functions left, amongst which is dust catching yes!


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What to do with C3g tubes. So I got a large amount of C3g tubes and Im looking for projects that fits this tube perfectly So what can you really do with these tubes? They are really great tubes, the curves look beautiful and the build quality is superb I feel bad to let them waste away on a shelf so enlighten me! Well, you can send 4 of those for me , i never had one of those, and could include them in my next project. Originally Posted by adalin.

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