I recently finished an IT coupled 300b amp. I am using Gui Guang 300b I bought a few years ago as spares and to use in prototyping so as not to ruin expensive 300bs
They use fixed bias and since WE data sheet say the maximum current is 70ma I adjusted them to that value. The measured values for plate voltage and grid voltage did not match the plate curves of the WE data sheet Everything works in the sense that it makes music After some thought I had a look at the plate curves for the 2A3-40 and my measurements fit the plate curves of this tube very closely
I know this is just my experience with an inexpensive Chinese tube but it does go some way to support the notion I read once that few current production 300Bs are real 300Bs I would be delighted to hear of other people's experiences and opinions
They use fixed bias and since WE data sheet say the maximum current is 70ma I adjusted them to that value. The measured values for plate voltage and grid voltage did not match the plate curves of the WE data sheet Everything works in the sense that it makes music After some thought I had a look at the plate curves for the 2A3-40 and my measurements fit the plate curves of this tube very closelyI know this is just my experience with an inexpensive Chinese tube but it does go some way to support the notion I read once that few current production 300Bs are real 300Bs
I would be delighted to hear of other people's experiences and opinionsI would agree that a lot of cheap, current-manufacture 300Bs do not match the original WE specs. It's possible that you got a 300B-like tube that's more like a 2A3 with 5V filaments. It wouldn't surprise me, since I've seen modern-made 2A3s that look like 300Bs with 2.5V filaments. It's possible that the manufacturer used pretty much the same innards. If they work, they work, but you won't get the same power output you would with a better-spec'd tube.
I know this is just my experience with an inexpensive Chinese tube but it does go some way to support the notion I read once that few current production 300Bs are real 300Bs
My experience with Chinese 300B's is that if they are properly selected they are just fine and provide very good performance.
People associate low quality to Chinese products by default because the large scale production comes from there and so one can find good and bad stuff.
But as I said, proper selection (or good luck!) eliminates the problem. On top of that, a number of expensive tubes rebranded in some other country are made in China with very same tools and materials...they are just selected following strict rules! And there are specific Chinese brands like the most recent Linlai who make high quality stuff.
So don't be afraid of using your Chinese 300B's if they work fine. Maybe you should do (or ask someone to do it if you can't) some measurements and see what you are getting. But listening rarely gives the wrong response....
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I've measured a bunch of WE, European new manufacture eg. JJ, AVVT, Emm Labs, and what are now slightly older Chinese 300b eg. Sophia Princess, Shuguang, TJ. The stand out difference is the noise. Maybe not audible but when trying to balance out the emissions to check the transconducance it has been damn near impossible to do this accurately with the Chinese tubes. I personally take that to mean that these tubes are still out gassing from their micas or metals, or else incompletely evacuated. I don't think this points to continued long term performance.
I have to say I haven't had one fail on me though, unlike EH 300b which are a bit of a liability, and I also have no problems with how they sound in my amps, flavours only as others have mentioned. So far they have all measured like 300b, and the Valve Art 2A3 measure like 2A3 [emoji846]
I have to say I haven't had one fail on me though, unlike EH 300b which are a bit of a liability, and I also have no problems with how they sound in my amps, flavours only as others have mentioned. So far they have all measured like 300b, and the Valve Art 2A3 measure like 2A3 [emoji846]
Sheep in wolf's clothing?
The only thing that really bothers me about this is that it makes it difficult to verify a design from measurements taken that do not match the expectations one might form based on WE 300B data sheet Sure, they work but if they are really 2A3s with a 5 volt filament it raises doubt about tube longevity, at least in my mind since they are being pushed fairly hard in this circuit
The only thing that really bothers me about this is that it makes it difficult to verify a design from measurements taken that do not match the expectations one might form based on WE 300B data sheet
Sure, they work but if they are really 2A3s with a 5 volt filament it raises doubt about tube longevity, at least in my mind since they are being pushed fairly hard in this circuit
Just to be clear, I meant measure the output power and distortion of the amplifier.
If want to measure the tubes only one needs to be careful as many supposed 300B's are not exactly the same as the original. Very close but not identical. So most tube testers with a fixed measurement set-up might give the wrong answer. Wrong answer in the sense that the good/discard values might not be valid as the bias conditions are a bit different. Some tubes might measure even below the minimum for a good tube reported in the tube tester manual while in reality they are pretty good.
If want to measure the tubes only one needs to be careful as many supposed 300B's are not exactly the same as the original. Very close but not identical. So most tube testers with a fixed measurement set-up might give the wrong answer. Wrong answer in the sense that the good/discard values might not be valid as the bias conditions are a bit different. Some tubes might measure even below the minimum for a good tube reported in the tube tester manual while in reality they are pretty good.
That is to say that many tubes purporting to be 300Bs are not in fact anything near the original
Well, the point is that even if they are not exact copies they are close and the performance one gets from the amplifier with good tubes is the same. It's really at hair splitting levels. This also means that tube rolling is generally a bad idea, unless one has a badly set-up amplifier and by change finds the right tube. But that is quite expensive practice, IMHO. The outcome might give a wrong impression tough....some tubes are better than others but in reality it's not really true.
The originals are so expensive I would never buy them unless I were rich and had nothing better to do with my money....
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It's not the tube. It's amplifier that sounds like that with two different tubes because the PSVane with punched plate (mesh is another thing with true wires) is different.
I still remember the 45/n Fullmusic with that kind of punched plate. It had nothing to do with a 45. It only happened to bias at 36 mA at 250V/-50V but for the rest not really a substitute with about 20% more gain and 40-50% more gm! A nice tube in its own right but not a 45.
I had a pair of Mesh-plate "300B" tubes.
Unfortunately, one tube developed excessive grid current, and could not be used with RC coupling at any reasonable Rg resistance. A very low impedance driver output would have been required, and a much larger coupling cap to go along with the low value Rg.
I did not want to have to go back to using interstage transformers, so the offending tube went into the circular file can . . .
Just my solution, yours may have been different.
Unfortunately, one tube developed excessive grid current, and could not be used with RC coupling at any reasonable Rg resistance. A very low impedance driver output would have been required, and a much larger coupling cap to go along with the low value Rg.
I did not want to have to go back to using interstage transformers, so the offending tube went into the circular file can . . .
Just my solution, yours may have been different.
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Which version of WE-300B do you have? The general opinion is that the 80's and 90's versions do not sound very great, at least far from the level of those made in early days.
Not sure about the current production version though. Very curious to find out.
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