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Western Electric 300B

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kokoriantz,

I have written on some other threads on this site, about the effect of DC filaments and what portion of the filament provides a larger portion of the plate current. It seems nobody wants to believe me.

I find it interesting that Western Electric says when using a DC filament supply, they say to have the negative end of the filament at ground (or at the self bias resistor). They say the grid bias correction is 3.5V versus the curves for AC filaments. I always knew the 'center' of the current from different portions of the filament that goes to the plate was not the physical center of the filament The physical center is 5V/2 = 2.5V. But consider the bias correction of 3.5V versus the physical center of 2.5V. Maybe they do not want to believe Western Electric either. Oh well.
 
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pieter t,

You are right. There are only 4 external pins on the 300B. But please read on . . .

I am sorry I did not explain what I meant by the 'center tapped filament'. We are talking about the 300B 'internal' filament. It is either a V and a V (two Vs), or it is a W (sorry again, my word processor does not allow me to turn the V and W upside down).

Take a look at the Western Electric 300B, there is an inverted V at one side, and an inverted V at the other side. The outside of the left V is connected to the outside of the right V. That is one connection, and it goes to one of the 4 pins. The center of one V is connected to the center of the other V, and it goes to one of the 4 pins. That means there is a V filament on the left with 5 Volts across it, and there is a V filament on the right with 5 Volts across it. With a DC filament supply, It is either +5V, 0V, +5V across the tube; or 0V, +5V, 0V across the tube. They have connected the two Vs in parallel, each V has 5 Volts across it, but each V covers only 1/2 of the plate. With an AC filament supply, it is +/-5V, 0V, -/+5V.

There are some manufacturers who use a different connection of the 300B tube's filament internally. It is a W not a double-V. The 5 Volts starts at the left, goes along the whole W, and ends at the right. With a DC filament supply, it is either +5V, 0V across the whole filament; or 0V, +5V across the whole filament. That means the middle of the W has +2.5V. For the physical center of the W filament +2.5V is quite different than 0V at the physical center of the V V filament. With an AC filament supply, the W is +/-5V, 0V across the ends of the filament. The one W filament covers the whole plate.

If you had a 300B of each type, you could easily see this inside the tube.

By the way, the JJ 40W 2A3 has two V filaments, ties them together at the outsides, and ties them together at the insides. That means that for DC filaments the filament voltage across the plate structure is either + 2.5V, 0V; or 0V, +2.5V. And for AC filaments, the filament voltage across the plate structure is effectively +/- 1.25V, -/+ 1.25V.

It is a little hard to see at first. Does that explain it for you?
 
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Thanks for the explanation.
I understand that there are two filament structures effectively paralleled with two terminations to the socket, one of these called "center tap" because it comes from the "middle".
However, this is different from a real center tapped filament, which, for a 300B would need a 2,5-0-2,5V supply, so the term "center tap" is misleading at least.
 
pieter t,

True, the 12AU7 is a center tapped filament tube, can be wired either as 12.6V or 6.3V, because it has 3 filament pins.

I forgot about how many Vs or Ws are in the following tubes:

The 300B has 2 Ws. For most 300B the filaments have a connecting wire from the left to the right end, and the middle of the two Ws is the other connection.

The JJ 300B connects one pin to the left end, and the other pin to the right end of the whole long 2 W string. I have never had a JJ 300B die, they still all work.

The 45 has a single W. 1.5A

The dual plate 2A3 has a single W in each plate, but the 2 W filaments are connected in parallel. Each W is 1.25A, but since they are in parallel, 2.5A total.

The modern single plate '2A3' has 2 Ws, and they have a wire connecting the left to the right ends of the 2 Ws, and the center of the 2 Ws is the other lead. Each W is 1.25A, but since they are in parallel, 2.5A total. JJ, Sovtek, and Electro Harmonix are all this way. But remember the JJ 2A3 can dissipate 40 Watts.

(no, I have never even seen the original single plate 2A3 with 21 filaments).
 
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I have 20 year old JJ 300Bs that are still just fine with more than 5000 hours of use. Last time I tested them years ago they still had more than 90% of their initial transconductance - these days they are spares in the event of a mishap with one of the newer sets. (I have 4 channels of 300B amplification currently in use)
 
I received an update email from the folks at Western Electric. Those who are subscribed to the Western Electric email list will be getting an update soon, which should have some in-progress videos. It would be exciting to see the process of setting up the factory floor as I really enjoy that sort of thing, but I’ll just have to be patient until the next visit in the fall. These are some pictures shared. Not a lot to show at this point but I’m still excited.
 

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Still haven’t been to visit the fine folks at the Western Electric Rossville Works as they haven’t been ready for me to do so. Just received this link in my email. I enjoy these videos, hopefully there is someone else here that does too. I’m still excited about the arrival of this tube from it original manufacturer.
YouTube
 
I have to say that even at these crazy prices, I don't see them making a big profit unless they're using old production kit. I'm sure it'll be good for their prestige though.

Looking at the (small section) of the production reminded me of a TV repair shop I worked at in the 60s where we would re-gun CRTs in the basement. I can still remember the process - and the enormous explosions that sometimes occurred during vacuum pumping in the oven. Those were crazy days.
 
According to the website and viewing the video, they are using a lot of the old process equipment. It's no trivial matter to reproduce the old processes and improve on them. Some people say that the new tubes won't sound as good as the old tubes. I congratulate anyone who can actually hear these differences. Frankly Charlotte, I can't. However, I will purchase a set of new 300Bs from Western Electric. They have a great warranty, and I appreciate the engineering, time, effort and money that is going into this entire enterprise.
 
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