12AU7 was a lower heater power and Pd low mu tube. It was designed to replace the 6SN7/6CG7 but not electrically. Just as a low mu tube with lower heater current. Personally, I think it's gross as a gain tube without CCS or LED or other work arounds. Not a bad cathode follower though. 
If the 6AK5 is a 6J1P then I like them triode strapped - they make a great cheap triode gain stage with low-medium mu.
6DJ8 is a great tube but expensive compared to some alternatives... If I design from scratch, I don't design for 6DJ8, but for 6N1P etc (And the 6N3 is a great tube) - the 6DJ8 will work anyway if you need to use it.
If the 6AK5 is a 6J1P then I like them triode strapped - they make a great cheap triode gain stage with low-medium mu.
6DJ8 is a great tube but expensive compared to some alternatives... If I design from scratch, I don't design for 6DJ8, but for 6N1P etc (And the 6N3 is a great tube) - the 6DJ8 will work anyway if you need to use it.
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Id have to say it depends too much on the application. We live in a world that deals in generalizations too much.
Im sorry if i'm gonna ignore the question. I am just going to give my subjective opinion on the matter.
The 6DJ8/ECC88 is a great very linear dual triode with low capacitances. But there are some types that blow this tube out of the water when it comes to Linearity and are available still if you know where to look or what the equivalents are.
The 12AU7 and the 6SN7 are somewhat less linear, but easier to design with for the novice cause if you use the 6DJ8 wrong it will oscillate at very high frequencies. and most people don't have a Oscilloscope over 20Mhz so will never notice.
Furthermore the 12AU7 and 6SN7 are specified for higher voltages, so if you need more swing these will swing slightly more than the 6DJ8
Furthermore the 6DJ8 should never be used with more than 200V supply voltage. People don't read data sheets, so there are professional products that go through these like crazy.. Shame cause they are nice tubes.
There where far better tubes produced from a technical standpoint. Some tubes that will never be made again because their application disappeared.
The EF184 was perhaps one of the most produced tubes and is quite good if you put it in triode and CCS plate load it.
EF184 is a frame grid pentode with frame grid G1 and G2? im not so sure about the screen grid, its been a while since i took one apart. But if you plate load it with a CCS you can get quite linear amplification out of this.
Suggested operating points are : 10M45S plate load set at 15mA. 1.8V Red led bias. and about 150V over the tube. at that dissipation you are running them about 90% of combined anode and G2 dissipation so they will last somewhat shorter.
Plate resistance is about 4K in this configuration.
Gain is about 50 in this topology, enough to drive most SET amplifiers into clipping.
Cheers,
V4lve
Im sorry if i'm gonna ignore the question. I am just going to give my subjective opinion on the matter.
The 6DJ8/ECC88 is a great very linear dual triode with low capacitances. But there are some types that blow this tube out of the water when it comes to Linearity and are available still if you know where to look or what the equivalents are.
The 12AU7 and the 6SN7 are somewhat less linear, but easier to design with for the novice cause if you use the 6DJ8 wrong it will oscillate at very high frequencies. and most people don't have a Oscilloscope over 20Mhz so will never notice.
Furthermore the 12AU7 and 6SN7 are specified for higher voltages, so if you need more swing these will swing slightly more than the 6DJ8
Furthermore the 6DJ8 should never be used with more than 200V supply voltage. People don't read data sheets, so there are professional products that go through these like crazy.. Shame cause they are nice tubes.
There where far better tubes produced from a technical standpoint. Some tubes that will never be made again because their application disappeared.
The EF184 was perhaps one of the most produced tubes and is quite good if you put it in triode and CCS plate load it.
EF184 is a frame grid pentode with frame grid G1 and G2? im not so sure about the screen grid, its been a while since i took one apart. But if you plate load it with a CCS you can get quite linear amplification out of this.
Suggested operating points are : 10M45S plate load set at 15mA. 1.8V Red led bias. and about 150V over the tube. at that dissipation you are running them about 90% of combined anode and G2 dissipation so they will last somewhat shorter.
Plate resistance is about 4K in this configuration.
Gain is about 50 in this topology, enough to drive most SET amplifiers into clipping.
Cheers,
V4lve
Incredible80, what exactly are you trying to achieve by doing a “poll” on three dissimilar tubes?
If you wear size 10 shoes, you will be able to put your feet into a pair of size 11 shoes. That does NOT mean they fit.
No, but they still function as shoes. A big comfy shoe is great when you're standing around (idle) but falls apart when you have to run somewhere. One size out isn't that bad lol. In the case of the tubes though, there must be a jumper of something for the heater pinout? And is it a precision timebase oscillator or a generic voltage amplifier? In the case of the latter, any tube will do for the most part.
And regarding the low plate voltage of a 6DJ8. It was designed for cascode. The low plate voltage spec represents a desire for them not to blow up if you didn't elevate the heater. If you respect the man Vhk, your chances are good that a 6DJ8 will work with 300+ plate volts.
And regarding the low plate voltage of a 6DJ8. It was designed for cascode. The low plate voltage spec represents a desire for them not to blow up if you didn't elevate the heater. If you respect the man Vhk, your chances are good that a 6DJ8 will work with 300+ plate volts.
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There are amps that have a switch that allows the user to use a 12AU7 and 6DJ8, take a Little Bear P10 for example
Supply and demand, that and some individuals have 1000s of them. Most tube aficionados are hoarders. Some are crazy hoarders. The Suppliers like BTB have 2M tubes on the shelf.
In the 80s you could go to swapmeets and buy garbage bags full of tubes. They where considered useless at the time. People where just throwing tubes away or using them as target practice for an air gun. Back near the end of tube production stuff got crazy, some companies that didnt want to fire their workers kept making tubes take them out of the factory and put them in a shredder someplace else.
There is a LOT of stuff still out there with HAM radio folks and vintage radio enthousiasts. Hell i know a few collectors that are sitting on 10.000 plus tubes. But these people have daytime jobs and no desire to sell them or need the money.
Im a small time collector but have over 2000 audio suitable tubes...
The tube marked in my mind is just stamp collecting, and loads of people trying to make a buck out of people that don't know where to get stuff. Or are selling some weird *** tubes to collectors with deep pockets.. You can sell anything by claiming it sounds nice.
Case and point, there was a collector near where i live who passed away. And he was rumoured to have millions of tubes. I saw used tubes by the bucket when his relatives started selling of the tubes.
They had so many old radios, they where asking 25 euro's for a radio, but inside was a GEC PX25 that they didnt notice, because they had no clue it was there.
They had boxes upon boxes of tube sockets.. I got like 12 sockets for RL12P35 there.. Some WE sockets for 101D (really nice stuff but hugely overpriced on ebay)
Another Anecdote was that when Philips shut down production of tubes in Eindhoven in 88 there was a last batch of EL34 made to commemorate almost 60 years of tube making by them. There is a Dutch expression that translates into : putting a dot behind something. Used in a variety of contexts, but is commonly accepted to mean to put something to rest, or to finish something.
The last batch of tubes made by Philips are EL.34 or EL34.
There was a news article in 88 that i can cite as saying "Philips zet een punt achter radiobuizenproductie"
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What's your favorite type of hammer?
A claw hammer? . . . A rubber mallet? . . . A tack hammer? . . . A sledgehammer?
What are you trying to build? As with hammers, it depends on the specifics of the job.
Rather than posting a meaningless poll, you might consider starting a thread with a title that is more specific. e.g. What preamp tubes work well with 24v on plate?
Actually, I would suspect that the most commonly used in commercial products would be the 12AX7.
Now, if you're talking about the cheap, low voltage, Chinese preamps like the FX, then the 6AK5 family is the most common in those applications.
The low voltage used in the FX, which is actually higher than 24v, limits its performance. Most tubes are designed to run at higher voltages, including all of the ones you mentioned. You can find their data sheets here:
Frank's electron Tube Data sheets
If you're going to build something, why start with a voltage that restricts performance? Or, as suggested above, start with a tube that's designed for low voltage.
Don't care at all, they can all be designed in by anyone who knows how. They are just toobs, not diamonds in the rough. Give yourself a shake!!
I don't know what you're trying to ask here. These types are completely different. The 12AU7 is a general purpose VT that does have characteristics superficially similar to the 6SN7, but was mainly intended for RF and quasidigital service as a oscillator/buffer, singly balanced mixer, intermediate Class C driver/frequency tripler/low power final, multivibrator, One Shots, Schmidt Trigger, RS-latch. Its audio characteristics are a good deal less linear than the 6SN7, making good audio loadlines hard to find, though it works well as a cathode follower grid driver.
The 6DJ8 was intended for use as a VHF cascode, small signal amp. It can be used for audio, either as a cascode, or LTP phase splitter.
The 6AK5 is a small signal pentode that operates to 400MHz. You can find good operating points for audio in case you need that much gain. Its main application was as the front end for VHF converters or distributed amps with very wide bandwidth.
Very different characteristics.
Can i reflect on behalf of the forum? There is an add-age that says no question too stupid. And yet here we are tearing into the FNG for not knowing his glass.
The younger kids tend to get put off by this kind of behavior, Im also on reddit that has a much younger crowd. I can vividly remember a topic on another forum that called this forum a bunch of sour boomers.
Im 25 but i have sold most of the megabucks collectible stuff so far, betting that not enough people will pick up the hobby, so i can buy back what i sold at estate sales once the baby boom generation kicks the bucket.
If you like something, to an extent you are on a forum dedicated to the topic, you shouldn't attack those who don't know, but try to pass on the knowledge.
The younger kids tend to get put off by this kind of behavior, Im also on reddit that has a much younger crowd. I can vividly remember a topic on another forum that called this forum a bunch of sour boomers.
Im 25 but i have sold most of the megabucks collectible stuff so far, betting that not enough people will pick up the hobby, so i can buy back what i sold at estate sales once the baby boom generation kicks the bucket.
If you like something, to an extent you are on a forum dedicated to the topic, you shouldn't attack those who don't know, but try to pass on the knowledge.
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What tubes were designed for can be a mystery.
Up to engineers.
Up to marketeers.
Up to the person working contracts with the government during wartime?
And, as time moved on, the war ended, solid state ramped up, the call came to marketing to find new markets for this tube.
What engineers did with them after all that is up to them.
Creativity is great!
Oops, I just thought of my National Instruments decades-old J-FET book.
It listed different process chips that were used for amplifiers, switches, etc.
Sometimes the same process was used for many J-FET type numbers across all those applications.
Welcome to creativity.
Welcome to engineering
Welcome to marketing
Up to engineers.
Up to marketeers.
Up to the person working contracts with the government during wartime?
And, as time moved on, the war ended, solid state ramped up, the call came to marketing to find new markets for this tube.
What engineers did with them after all that is up to them.
Creativity is great!
Oops, I just thought of my National Instruments decades-old J-FET book.
It listed different process chips that were used for amplifiers, switches, etc.
Sometimes the same process was used for many J-FET type numbers across all those applications.
Welcome to creativity.
Welcome to engineering
Welcome to marketing
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OK.
Back to the original poster's question, Quote:
"why does some amp can run on both 12AU7 and 6DJ8?"
Original poster: What amplifier are you talking about?
What amplifier does anybody know that can run on both a 12AU7 and a 6DJ8.
Does it do that by using 2 different sockets?
Does it do that by using switches?
Or, does the [stereo] amplifier have 2 stages for each channel, one socket for only 12AU7, and another socket for only 6DJ8?
Is the question why would an amplifier use both a 12AU7 in one circuit, and a 6DJ8 in another circuit (like why doesn't the designer just use the same type of tube for both stages, either two 6DJ8 or two 12AU7)?
The filaments of both tube types can not both work properly on a single socket, unless there is a filament re-wiring switch.
So, again, what amplifier is the original poster talking about?
Commercial product?
DIY project?
And no, an ECC86 and 6DJ8 will not work with a 12AU7 socket that is wired for 12V.
And no, a 12AU7 will not work with a socket wired for a 6DJ8 and a ECC88 (6.3V filament wiring, pins 4 to 5).
To operate a 12AU7 on 6.3V requires a completely different wiring to the socket, pin 4 strapped to pin 5, and the other end of 6.3 to pin 9.
This is a case of Plug and Pray, not a case of Plug and Play.
Back to the original poster's question, Quote:
"why does some amp can run on both 12AU7 and 6DJ8?"
Original poster: What amplifier are you talking about?
What amplifier does anybody know that can run on both a 12AU7 and a 6DJ8.
Does it do that by using 2 different sockets?
Does it do that by using switches?
Or, does the [stereo] amplifier have 2 stages for each channel, one socket for only 12AU7, and another socket for only 6DJ8?
Is the question why would an amplifier use both a 12AU7 in one circuit, and a 6DJ8 in another circuit (like why doesn't the designer just use the same type of tube for both stages, either two 6DJ8 or two 12AU7)?
The filaments of both tube types can not both work properly on a single socket, unless there is a filament re-wiring switch.
So, again, what amplifier is the original poster talking about?
Commercial product?
DIY project?
And no, an ECC86 and 6DJ8 will not work with a 12AU7 socket that is wired for 12V.
And no, a 12AU7 will not work with a socket wired for a 6DJ8 and a ECC88 (6.3V filament wiring, pins 4 to 5).
To operate a 12AU7 on 6.3V requires a completely different wiring to the socket, pin 4 strapped to pin 5, and the other end of 6.3 to pin 9.
This is a case of Plug and Pray, not a case of Plug and Play.
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as long as the filaments are fed correctly, they should all work.....
the 12au7 are not plug in replacements to the 6dj8....
unless you do something tot he filament connections correctly...
for the 6dj8, a 7dj8 will work, so will a 6bq7,6bk7, even 6cg7 6fq7, 6gu7....
my favorite 6dj8 is the Russian 6H23......ask Anatoliy...
the 12au7 are not plug in replacements to the 6dj8....
unless you do something tot he filament connections correctly...
for the 6dj8, a 7dj8 will work, so will a 6bq7,6bk7, even 6cg7 6fq7, 6gu7....
my favorite 6dj8 is the Russian 6H23......ask Anatoliy...
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