I already said above that I once had 100 European radio tubes of various kinds. They lingered on eBay for around a year and the only ones that sold were to the Far East. I also put them on a Wireless forum. I sold less than a dozen to radio restorers.
Judging from my actual experiences with European radio tubes, the demand for radio tubes is tiny. Some restorers said they already had enough reserve stocks for the radios they commonly restored. Plus bear in mind that many tubes used in radios are of no interest to audio amp builders. So I'm not inclined to lose any sleep over using vintage tubes.
Would single sheet or open box type anodes be a version of that along the way to closed box anodes?
Yes, same design goal. It might be seen as a mesh with a very coarse pitch.
it was/is done just the same aim - to prevent overheating of Grid.1.
Here's one of my splendid Mullard (Blackburn) PL802 frame grid super-gm (40mA/V) pentodes:
The anode, and other grids are open to prevent grid.1 from severe overheating. The frame-grid architecture was pushed to the maximum to achieve such a high slope, meaning the clearance from the cathode was as small as they dare go.
The PL802 probably did not have profitable manufacturing yields; a solid state plug-in was introduced for TV receivers later. (Restorers can use these and leave the Blackburn beauties for high-gain audio stages they are so well suited to)
Its performance may well depend on taking care to keep the 300mA heater current well controlled.
it was/is done just the same aim - to prevent overheating of Grid.1.
Here's one of my splendid Mullard (Blackburn) PL802 frame grid super-gm (40mA/V) pentodes:
The anode, and other grids are open to prevent grid.1 from severe overheating. The frame-grid architecture was pushed to the maximum to achieve such a high slope, meaning the clearance from the cathode was as small as they dare go.
The PL802 probably did not have profitable manufacturing yields; a solid state plug-in was introduced for TV receivers later. (Restorers can use these and leave the Blackburn beauties for high-gain audio stages they are so well suited to)
Its performance may well depend on taking care to keep the 300mA heater current well controlled.
The example above shows that the same objective was (and is) achieved by modified means.
Not only by improved cooling.....
Many later designs used gold-plated grids. The gold layer is less given to electron emission; and the surface is also less likely to accumulate particles of emissive material escaped from the cathode.
Only a thin layer is required - as low as 1µm. Even low-cost connectors are available with this kind of gold-plating - meaning the process is relatively low-cost; lower than making mesh anodes, for sure.
Last time I looked, EML offered 300B/DHT variants with both MESH anodes AND gold-plated grids.
All of EML's DHTs have gold plated grids, IIRC.
I'm not convinced. As you've pointed out, gold plating is a cheap way to reduce grid thermal emission, and winding the grid on copper support rods leading to radiant fins was done by Mullard to cool grids (EL34). Noting that the PL802 was intended to be a video output valve when 625 line television had just been introduced, it would have needed to be good to 5.5MHz, so it seems more likely that the open structure was to reduce inter-electrode capacitances.
Hi mbrennwa,
Now you're putting words into my mouth. George has done a lot of experimenting, and that is what he is into. I respect George a great deal, and I don't agree with that use of a scare resource. But mindlessly using these tubes all over a fad doesn't cut it.
People can tell themselves anything that justifies their actions to make themselves feel better. But when you take a long view look at the situation the answers are pretty clear. To be honest, if there were box cars of these tubes available cheap, then I wouldn't have any problem with it. It would still be a waste of money, but it would hurt anyone else.
Yes, gold plated grids were used to prevent secondary emission, also to reduce contamination from the cathode material. The lower grid temperature reduces activating any material deposited on the grid wires. Primary emission begins at higher temperatures. Allowing heaters to run full current without plate current encourages grid contamination.
You can drag up isoated examples of tube construction to "prove" any point you want to make. Manufacturers have tried many things. But if you look at how tubes are constructed on average and over time, that tells you the truth.
Now you're putting words into my mouth. George has done a lot of experimenting, and that is what he is into. I respect George a great deal, and I don't agree with that use of a scare resource. But mindlessly using these tubes all over a fad doesn't cut it.
People can tell themselves anything that justifies their actions to make themselves feel better. But when you take a long view look at the situation the answers are pretty clear. To be honest, if there were box cars of these tubes available cheap, then I wouldn't have any problem with it. It would still be a waste of money, but it would hurt anyone else.
Yes, gold plated grids were used to prevent secondary emission, also to reduce contamination from the cathode material. The lower grid temperature reduces activating any material deposited on the grid wires. Primary emission begins at higher temperatures. Allowing heaters to run full current without plate current encourages grid contamination.
You can drag up isoated examples of tube construction to "prove" any point you want to make. Manufacturers have tried many things. But if you look at how tubes are constructed on average and over time, that tells you the truth.
Maybe there should be a list of endangered tubes so we accept that the use of some variants could jeopardise the preservation of historical equipment. There are plenty of old types that have seemingly unquenchable supplies, 6SN7s and 807s seem to be like that. Others, like PX4s and AD1s, get pulled from working radios, and there will not be a cost effective way to get them operational again.
The PL802 had the PL802T, so perhaps the solution is the PX4T for renovations, and accept that the remaining stocks will be pressed into audiophile use?
The PL802 had the PL802T, so perhaps the solution is the PX4T for renovations, and accept that the remaining stocks will be pressed into audiophile use?
Well for sure there are boatloads of 26 and 01A tubes out there. I often pick them up at hamfests for $5 each!
As for my amps, the 833C DHT tubes are new manufacture from China, albeit using "vintage" names like Machlett and Taylor.
As for my amps, the 833C DHT tubes are new manufacture from China, albeit using "vintage" names like Machlett and Taylor.
We can test that idea easily enough by comparing the PL802 with one of the first IF pentodes to fall to my hand: the 6BW7.
These have similar dimensions of height and diameter of the anode... but the 6BW7 has a 360° solid anode, and a solid shield.
The PL802 has almost the same output capacitance as 6BW7: 4pF vs 3.5pF
But the PL802's Cag1 is 10x GREATER than the 6BW7's (0.1 vs 0.01pF) despite the 360° solid anode.
And so the 6BW7 is not only rated for 5.5MHz (no big deal - which fairly ordinary Power MOSFETs can reach) - it is intended for RF and IF applications.
One the other hand - the gm of the PL802 is 4x the 6BW7's; this makes the Grid.1 to cathode proportionately closer.
More importantly, the PL802's heater power is almost tripled, and even more tightly coupled to the grid. This means it will be very much hotter.
The need for drastic changes to keep the Grid.1 temperature under control is the only explanation that withstands any scrutiny.
Addendum:
Other IF pentodes, like EF183, EF184, 30F5, 6F23 have even lower Cag1 than 6BW7, and 10x or less compared to PL802; and these are constructed with 360° Mesh Anodes...
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Why no one is making 26 or 10 tubes anymore, is a question I have always asked. Especially with the boutique tube makers with totally made up tubes with the 99th version of a 300B that no one is asking for, instead of some really nice tubes like the 26/10/71/RS241/12A/RE604/KC3 etc etc. I'm guessing the unknowing masses just read somewhere that the 300B is the best tube and only want that, and I guess you can't charge $600 for a tube that can still be found NOS for <$100.
Also the "new tubes better" argument is that same as the people swearing by THD numbers as correlating to any sort of sound quality. Telling people they can't use old tubes in their amps is gate-keeping imo. So many tubes have been wasted, old and new, on bad designs. But who will determine when a design is good enough to use NOS tubes? We should talk about all the 300B, 50 and mono-plate 2A3, AD1 etc etc amps being driven by 12AX7s, now that is a combination that needs to be outlawed.
BTW: I've built spud amps with a single modern tube (437A, EC8010, 3A/167M, 5842, 6S45) and I have yet to hear one of these perfect new tubes that can not be beaten but a three stage DHT amp with tubes from 100 years ago and a bunch of transformers coupling them. The human ear is a better judge of sound quality than any electronic measuring device. If there was a device to quantify sound quality, everyone would be listening to the perfect amps already.
Also the "new tubes better" argument is that same as the people swearing by THD numbers as correlating to any sort of sound quality. Telling people they can't use old tubes in their amps is gate-keeping imo. So many tubes have been wasted, old and new, on bad designs. But who will determine when a design is good enough to use NOS tubes? We should talk about all the 300B, 50 and mono-plate 2A3, AD1 etc etc amps being driven by 12AX7s, now that is a combination that needs to be outlawed.
BTW: I've built spud amps with a single modern tube (437A, EC8010, 3A/167M, 5842, 6S45) and I have yet to hear one of these perfect new tubes that can not be beaten but a three stage DHT amp with tubes from 100 years ago and a bunch of transformers coupling them. The human ear is a better judge of sound quality than any electronic measuring device. If there was a device to quantify sound quality, everyone would be listening to the perfect amps already.
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I wonder if you could retrofit tubes with new filaments. Costly, but a way to preserve history?
That, and a 26 with TT filament!
That, and a 26 with TT filament!
'01A tubes are expensive up here and many are bad.
Any tube that is not current manufacture is on the endangered list. Then think of this. If that tube design was actually good (compared to later tubes), it would still be in production. If mesh plates did something useful, they would still be in production (we found better ways of dealing with the problems).
Remember, industry always would advance a product to be better technically and performance-wise. Poor products (compared to new designs) died in the marketplace. When I was young, I knew some real tube design engineers, long since passed away. They taught me the stark truth about tubes just about everything else with industry.
Most popular information comes from people who don't know, didn't work in the industry and were not engineers dealing with that product. They were not involved in failure analysis, but they did read what they wanted to read. Tube manufacturers designed and built what industry needed, and equipment design engineers told them what they needed. Equipment designers were pushing performance back then, be it consumer audio or military, industrial control or aeronautics. Consumer audio was a dwindling market, and later a very small percentage. You can thank musicians for the fact that we even have new tube equipment today. But, what is important to a musician is about opposite to what you want in a music reproduction system.
Any tube that is not current manufacture is on the endangered list. Then think of this. If that tube design was actually good (compared to later tubes), it would still be in production. If mesh plates did something useful, they would still be in production (we found better ways of dealing with the problems).
Remember, industry always would advance a product to be better technically and performance-wise. Poor products (compared to new designs) died in the marketplace. When I was young, I knew some real tube design engineers, long since passed away. They taught me the stark truth about tubes just about everything else with industry.
Most popular information comes from people who don't know, didn't work in the industry and were not engineers dealing with that product. They were not involved in failure analysis, but they did read what they wanted to read. Tube manufacturers designed and built what industry needed, and equipment design engineers told them what they needed. Equipment designers were pushing performance back then, be it consumer audio or military, industrial control or aeronautics. Consumer audio was a dwindling market, and later a very small percentage. You can thank musicians for the fact that we even have new tube equipment today. But, what is important to a musician is about opposite to what you want in a music reproduction system.
Hi VT-52,
Sure, that would be both easy and expensive. You would be remanufacturing the tube. You would be much further ahead building new modified ones.
Essentially this is what happened. We changed from DHTs to heaters for consumer use. They increased electron emission and extended tube life by going to heaters. While they were at it, they improved other characteristics along with metallurgy and chemical cathode materials. What this created was each succeeding generation of a tube. Each more reliable and efficient than the previous one. So on until the last generation of tube development. Tubes are very highly engineered, early tubes didn't have the benefit of the knowledge that came before and we learned from each iteration.
Tube engineering evolved over a long period of time. A lot of very good engineering went into them to make them better. Tubes have some problems that lead to development of the transistor and it's various types. That battle was short lived and we know where the market went.
As I said before. Tubes are cool, they are fun. Each design sounds different. But, they are not as accurate or quiet as current good technology. But they are fun and look very cool in semidarkness. I have no problem with people using tube equipment. I understand it and enjoy it myself. I wonder if governments will some day outlaw tube gear due to inefficiency?
Sure, that would be both easy and expensive. You would be remanufacturing the tube. You would be much further ahead building new modified ones.
Essentially this is what happened. We changed from DHTs to heaters for consumer use. They increased electron emission and extended tube life by going to heaters. While they were at it, they improved other characteristics along with metallurgy and chemical cathode materials. What this created was each succeeding generation of a tube. Each more reliable and efficient than the previous one. So on until the last generation of tube development. Tubes are very highly engineered, early tubes didn't have the benefit of the knowledge that came before and we learned from each iteration.
Tube engineering evolved over a long period of time. A lot of very good engineering went into them to make them better. Tubes have some problems that lead to development of the transistor and it's various types. That battle was short lived and we know where the market went.
As I said before. Tubes are cool, they are fun. Each design sounds different. But, they are not as accurate or quiet as current good technology. But they are fun and look very cool in semidarkness. I have no problem with people using tube equipment. I understand it and enjoy it myself. I wonder if governments will some day outlaw tube gear due to inefficiency?
Just to stir the pot, one might argue that a modern DIY or commercial preamp/amp/DAC is a better use of old tubes than an outdated, sounds-like-a-tin-can-on-a-string radio.
If I were a 01A, I'd rather be singing the classics in high fidelity than emitting scratchy AM radio pablum.
If I were a 01A, I'd rather be singing the classics in high fidelity than emitting scratchy AM radio pablum.
I keep saying that a 300b driven by a 12AX7 is just as much of a 12AX7 amp, but people still think of it as a "DHT amp".
Yes, an all-DHT amp is special. But I've built a 2 stage amp with 26 driving 4P1L PSE. That way I get enough gain, and it sounds lovely as you would expect.
And last time I checked, the purpose of these devices is for us to listen to them with our ears, they were not designed simply to be measured or used as a data transfer device between pieces of equipment. To relegate the decision of "What tube should be used" or what circuit is best based on mathematical models and testing audio equipment with non-music waveforms, in my experience doesn't equate to what I enjoy listening to.
So add me to the list of people to hate for using old tubes, I quite enjoy listening to my globe tube amp which uses a 80, two 47 and two 27 tubes. And I agree the mesh plate 27 tubes sound better than the solid plate versions, even if electrically they should be equivalent and according to some folks on various forums: all tubes of the same type should sound identical. I also enjoy listening to an EL34 amp I built that uses 6SQ7 tubes as the driver tube.
https://www.skunkiedesigns.com/47-globe-tube-amp
You write this as being a given fact when the reality is you left out the main criteria for industry: cost savings. Industry is known to give up a technically better and a higher performing product if they think they can get acceptable to the marketplace results at a lower cost. MP3 compressed audio is a prime example of this.
They also quit making the single plate 2A3 tube for the same reasons, they were too expensive to manufacture, not that the later dual plate tubes sound or perform better. The dual plate tubes were just much cheaper to make and in low-fi AM radio applications, were acceptable quality.
Hi Magz,
I wish most tubes used were in a responsible way. I have old radios, they don't sound too bad at all. The proper device installed in teh equipment designed for it is about the best use I can think of. You can design new stuff for anything.
Hi stephe,
I can't disagree with you. Well designed stuff sounds good no matter the device you use. Tube stuff is very much a preference thing, and it is cool, fun. Some tube stuff sounds extremely good. Tube stuff will always be noisy than solid state though. It may not matter.
One thing I have noticed. The better tube and solid state get, the more they sound the same. Shocking but true. That's because you are approaching perfection and the technology doesn't matter. Cost of ownership might, especially for the person who owns stuff like Conrad Johnson Premier One.
I wish most tubes used were in a responsible way. I have old radios, they don't sound too bad at all. The proper device installed in teh equipment designed for it is about the best use I can think of. You can design new stuff for anything.
Hi stephe,
I can't disagree with you. Well designed stuff sounds good no matter the device you use. Tube stuff is very much a preference thing, and it is cool, fun. Some tube stuff sounds extremely good. Tube stuff will always be noisy than solid state though. It may not matter.
One thing I have noticed. The better tube and solid state get, the more they sound the same. Shocking but true. That's because you are approaching perfection and the technology doesn't matter. Cost of ownership might, especially for the person who owns stuff like Conrad Johnson Premier One.
Hi stephe,
2A3 tubes were phased out due to inefficiency. Dual plate tubes were better. Look at battery power costs, your average user had to pay for power. Tubes had to take performance and running costs into consideration. Tubes are never discontinued solely due to production costs. If they sell, they will make them. If there is something better that performs the same function, the original will die. If that new something is cheaper, the death of the older product is quicker.
About the only irresponsible industries I can think of are recent history, and audio plus automotive are the shinning examples of how to put profit above everything else. But back in the day it was all about real performance vs all costs. Performance was not sacrificed as some romantic folks would like to believe.
Not entirely true at all. You can engineer higher performance at lower cost. Engineering is all about not wasting money and getting high performance. The sales department may chop budgets, then the engineers design the best product for the money. In real electronics engineering, designs are for higher performance and reliability. If cost reductions are possible as well, then they will opt for that.
2A3 tubes were phased out due to inefficiency. Dual plate tubes were better. Look at battery power costs, your average user had to pay for power. Tubes had to take performance and running costs into consideration. Tubes are never discontinued solely due to production costs. If they sell, they will make them. If there is something better that performs the same function, the original will die. If that new something is cheaper, the death of the older product is quicker.
About the only irresponsible industries I can think of are recent history, and audio plus automotive are the shinning examples of how to put profit above everything else. But back in the day it was all about real performance vs all costs. Performance was not sacrificed as some romantic folks would like to believe.
Not sure mesh sounds better, not much comparison material out there. I liked the Telefunken mesh AZ1, plus the shape of that particular globe and the finish on those mesh anodes is just a cherry on top, a delight to look at: The eye wants something as well. I don't think I have had any real mesh (dht) signal tubes that I can think of.
@stephe Gorgeous amplifier!!! I think I watched your youtube video on that amplifier, correct?
@stephe Gorgeous amplifier!!! I think I watched your youtube video on that amplifier, correct?