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1. Driven close to maximum
2. Driven conservatively
DC filaments with voltage regs like Rod Colemans' or AC may also make a difference.
1. Driven close to maximum
2. Driven conservatively
DC filaments with voltage regs like Rod Colemans' or AC may also make a difference.
Yes, they are. The only real problem with Chinese tubes (and other current production as well) is that the large scale production ends up with a good amount of tubes that should not be sold for "critical" application at least....
Hi-Fi is a critical application if you want best performance.
Don't think that NOS tubes were different from this aspect except that bad/poor tubes were not sold as good ones. In fact they were not cheap at all.....
Maybe for 400v -62v (338v at plate) , 1K resistor, 62mA, would be 21W dissipation.
Would be reliable ?
Would be reliable ?
Those with solid plate and no strange features can run at 30W without issues.
Psvane I do not personally know but other things like Golden Dragon, Billington rebranded work at 420V/70 mA or 400V/75 mA without problems.
21W, I have never found to be a problem with ANY 300B. If there is a problem it's a defective tube....
Psvane I do not personally know but other things like Golden Dragon, Billington rebranded work at 420V/70 mA or 400V/75 mA without problems.
21W, I have never found to be a problem with ANY 300B. If there is a problem it's a defective tube....
The only 300B's I know that do not like to work at more than 25-26W are those with mesh plate (true mesh made with wires or punched solid plate, no difference really).
This includes the very expensive ones made in EU as well....
This includes the very expensive ones made in EU as well....
They are pretty hard to beat and amongst the cheapest 300b's right now. I would have no problem going for them.
Avoid the mesh plate variants. Only problems if you try to push them. If you want less power go for (even cheaper) China 2a3's.
Edit: I see that 45 mentioned not pushing mesh plate variants too much. I agree.
Avoid the mesh plate variants. Only problems if you try to push them. If you want less power go for (even cheaper) China 2a3's.
Edit: I see that 45 mentioned not pushing mesh plate variants too much. I agree.
Yes, DC filaments will reduce life. AC filaments will make them last longer.
But seriously speaking I would not base any decision on that.
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But more importantly, how do they sound?
Not all 300B tubes sound the same, even in the same amp and circuit.
My experience with these cheap china 300b's has been positive.
Consider the alternatives.... everything else is at a MUCH higher price.
I would rather sink the money into a far better PSU, driver circuit, iron... etc.
Consider the alternatives.... everything else is at a MUCH higher price.
I would rather sink the money into a far better PSU, driver circuit, iron... etc.
Rod Coleman would say the opposite from his experiences with 300b amps, which he uses in his own system. I can't remember his exact words but if you dig out his posts it should be there. I think it related to a more gradual warming up of the tube.
How do you see AC filaments as lasting longer?
It is "only theoretical" but it is also something I have observed over the years. All my "vintage" valves/tubes get AC filaments, especially if they are getting on in age.
They last longer with AC and the "decline" in power is much more gradual vs. DC. For me, WWII and earlier globe 1930's valves/tubes all get AC. Newer valves/tubes can have DC though. No problem here with that.
The theory:
1. An AC filament is freeing electrons at a lower temperature across a greater area of the filament than DC (for a given same energy input). This is inherent, due to the cyclical nature of AC. AC is easier on the whole filament than DC heater due to lower skin effect and peak fluctuations (joule heating is peak-to-peak in nature) on surface.
Yes, I admit that this difference is very small. However over a longer period of time AC should increase filament lifespan and perhaps increase trans-conductance vs. DC.
2. With DC you have no cycle, so no potential cooling or relief for weaker parts of the filament. There is an additional benefit to this. Invisible weak points in a filament simply never experience a relief cycle with DC. This suggests that deterioration will likely be faster with DC vs. AC too in potential "weak points" of the filament.
If you dissect a filament of an "expired" valve/tube, you will likely find that some of the filament still works (yes, I did this). So it is the "weak" links that determine whether or not it is "dead". It is rare that the complete length of the filament has been rendered useless. DC never has any cycle which gives these weak points even a tiny lower temperature fluctuation. 4th power is a step function with AC, it is not linear.
3. With AC, the movement of Electrons is effectively "standing" (like newton's cradle) and "Emitting". This is inherently more efficient than DC which has real electron "flow" through the resistive filament (plus "Emitting" of course). From a physics and chemistry perspective, DC will cause the filament to undergo chemical transformation (=age) more efficiently (=faster).
Even without considering other effects (mostly aging, heating effects) this is the simplest explanation I can provide. DC is theoretically less efficient than AC.
But if you prefer DC, then that is fine too. Maybe the difference is only a thousand hours use or so. Not a big deal, right? I just don't like to use DC on valves/tubes that are getting closer to 100 years old
Ian
They last longer with AC and the "decline" in power is much more gradual vs. DC. For me, WWII and earlier globe 1930's valves/tubes all get AC. Newer valves/tubes can have DC though. No problem here with that.
The theory:
1. An AC filament is freeing electrons at a lower temperature across a greater area of the filament than DC (for a given same energy input). This is inherent, due to the cyclical nature of AC. AC is easier on the whole filament than DC heater due to lower skin effect and peak fluctuations (joule heating is peak-to-peak in nature) on surface.
Yes, I admit that this difference is very small. However over a longer period of time AC should increase filament lifespan and perhaps increase trans-conductance vs. DC.
2. With DC you have no cycle, so no potential cooling or relief for weaker parts of the filament. There is an additional benefit to this. Invisible weak points in a filament simply never experience a relief cycle with DC. This suggests that deterioration will likely be faster with DC vs. AC too in potential "weak points" of the filament.
If you dissect a filament of an "expired" valve/tube, you will likely find that some of the filament still works (yes, I did this). So it is the "weak" links that determine whether or not it is "dead". It is rare that the complete length of the filament has been rendered useless. DC never has any cycle which gives these weak points even a tiny lower temperature fluctuation. 4th power is a step function with AC, it is not linear.
3. With AC, the movement of Electrons is effectively "standing" (like newton's cradle) and "Emitting". This is inherently more efficient than DC which has real electron "flow" through the resistive filament (plus "Emitting" of course). From a physics and chemistry perspective, DC will cause the filament to undergo chemical transformation (=age) more efficiently (=faster).
Even without considering other effects (mostly aging, heating effects) this is the simplest explanation I can provide. DC is theoretically less efficient than AC.
But if you prefer DC, then that is fine too. Maybe the difference is only a thousand hours use or so. Not a big deal, right? I just don't like to use DC on valves/tubes that are getting closer to 100 years old
Ian
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I’ve always had a level of comfort with AC as it avoids a steady state voltage gradient along the filament. But dreaded hum, if not adequately nulled out, and which may have been accepted in a living room in 1940 is not so tolerable today. Still, I got so sick and tired of posters pushing DC for-sale solutions that I won’t touch any of them with a barge pole regardless of their benefit.
I’m not at all worried about tube longevity, just buy another bulb and swap it in. It’s why they aren’t soldered onto the board.
I bought psvane 845 as I have confidence in the brand but I was careful to avoid any of the cheapest grades because you know everything produced is sold, there’s no weeding out of the long tail of less reliable tubes.
I’m not at all worried about tube longevity, just buy another bulb and swap it in. It’s why they aren’t soldered onto the board.
I bought psvane 845 as I have confidence in the brand but I was careful to avoid any of the cheapest grades because you know everything produced is sold, there’s no weeding out of the long tail of less reliable tubes.
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In low mu DHTs I have not seen any difference in tube life for sure. Some of the oldest directly heated tubes I use, like the 49, can only be run with DC supply. The hum is only the second issue for importance. The first is the IMD. Maybe someone might not hear a difference as his system (including the room acoustics) is masking but I do. This is especially evident in low power amps. Quite noticeable unlike many typical "audiophile component upgrades".....
Anyway, the voltage gradient across the filament in low mu DHTs is a small fraction of the bias voltage. Regarding the 300B this is 5V vs 65-70V bias minimum.
I can't see much trouble really. Objectively, if the datasheet says that both AC and DC can be used without mention of tube life it means that this is not relevant. If the filament is damaged or weak, AC heating will not do anything special.
If you check all telephone vacuum tubes, that had to run for 24 hours a day for years, they were all specified to run with DC heating ONLY. Then there also were special telephone tubes that had work in extreme conditions, like underwater, and last 20 years.
http://www.ase-museoedelpro.org/Museo_Edelpro/Catalogo/tubes/records_nw/175HQ/175HQ_rec.pdf
All battery operated tubes should only be run with DC...and so on
Stable heating supply matters most! If you run filaments with unregulated supply and get some variance from power line that is going to affect tube life.
Anyway, the voltage gradient across the filament in low mu DHTs is a small fraction of the bias voltage. Regarding the 300B this is 5V vs 65-70V bias minimum.
I can't see much trouble really. Objectively, if the datasheet says that both AC and DC can be used without mention of tube life it means that this is not relevant. If the filament is damaged or weak, AC heating will not do anything special.
If you check all telephone vacuum tubes, that had to run for 24 hours a day for years, they were all specified to run with DC heating ONLY. Then there also were special telephone tubes that had work in extreme conditions, like underwater, and last 20 years.
http://www.ase-museoedelpro.org/Museo_Edelpro/Catalogo/tubes/records_nw/175HQ/175HQ_rec.pdf
All battery operated tubes should only be run with DC...and so on
Stable heating supply matters most! If you run filaments with unregulated supply and get some variance from power line that is going to affect tube life.
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If the AC filament voltage is a bit high (very frequently the case in my experience with filament transformers), then I could totally see a weaker/old tube performing better on AC. When filament emission capability is marginal, a little more filament power is going to help.
You'd have to strictly control for filament power to be sure that any difference in tube life is due to AC/DC, which would be impossible to do with conventional AC filaments since they are unregulated.
You'd have to strictly control for filament power to be sure that any difference in tube life is due to AC/DC, which would be impossible to do with conventional AC filaments since they are unregulated.
5V RMS equals the same heating value as 5VDC.
By definition.
Other effects may apply, but the total heat integrated over time is exactly equal.
By definition.
Other effects may apply, but the total heat integrated over time is exactly equal.
As I noted, for china valves/tubes it is not a consideration. And those ones from psvane are fine.
Ian
Ian
I agree with most of what you say but this little statement is simply not true.
Battery operated valves/tubes all run perfectly fine on AC. Sure, if they are directly heated then you might get some hum. But there is nothing electrically special about any heater to preclude AC from being used.
Perhaps I am unaware of some very specific valve/tube, but I doubt this.
Ian
It's not an opinion of mines Ian.
See for example the 49 which I have playing a lot with:
https://frank.pocnet.net/sheets/021/4/49.pdf
It says 2V D.C.
It doesn't say A.C. or D.C. as usual...you can check all of them. With battery tubes the gradient is really irrelevant as most of them, including the older ones, only require 1-2V filament voltage.
See for example the 49 which I have playing a lot with:
https://frank.pocnet.net/sheets/021/4/49.pdf
It says 2V D.C.
It doesn't say A.C. or D.C. as usual...you can check all of them. With battery tubes the gradient is really irrelevant as most of them, including the older ones, only require 1-2V filament voltage.
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When the filament voltage is comparable with bias there you start to see an impact on performance but not tube life.
For example the small power pentodes that have center tap to run the filament at 1.4V or 2.8V. With 1.4V (parallel mode) you get better performance:
https://frank.pocnet.net/sheets/127/3/3S4.pdf
Again a nice DC label is stamped right below the filament requirements....
For example the small power pentodes that have center tap to run the filament at 1.4V or 2.8V. With 1.4V (parallel mode) you get better performance:
https://frank.pocnet.net/sheets/127/3/3S4.pdf
Again a nice DC label is stamped right below the filament requirements....