Goal/purpose: Mr. E.Z. Tube is a cheap vacuum tube audio platform without the 'iron': no power transformer, no output transformer(s). A tube amplifier will typically have several heavy, expensive transformers: output transformers that protect speakers from high voltages in the tube, and power transformers that provide high voltage by rectifying mains (AC) power. Mr. E.Z. Tube eliminates both, but still uses popular high voltage tubes (EU:ECC81/2/3/4/5/8, American:12AT7/12AU7/etc.).

Mr. E.Z. Tube is definitely not audiophile gear - it is a platform for learning about tubes (bias, output/input capacitors, etc) without making a huge upfront investment in 'iron'. There are tons of tutorials on working with tubes, this is not one of them. This is a platform that helped me understand what the tutorials were talking about through hands-on experience.

Compatible with a variety of popular tubes (including tubes currently in production).
IR remote control interface (power, volume, 4 auxiliary outputs).
Cheap and easy SMPS (no 'iron'!).
I think it sounds great (but I have awful hearing).

Standard warnings apply: Mr. E.Z. Tube will not hesitate to kill you given the chance. Mr. E.Z. Tube can be run from batteries or an isolated DC wall-wart, but the same precautions apply as when working with a transformer and mains current!

Read on for more.

Step 1: Eliminating the 'iron'

Output transformer - to eliminate the output transformer we stick with a line amplifier design. Line amplifiers, unlike power amps, can be capacitor coupled. We still get to experience the joy of tube sound, but without the burden of driving speakers directly with tubes. In the picture below you can see a Mr. E.Z. Tube connected between a PC line-out and cheap PC speaker amplifier. My next instructable will cover the construction of a 'gainclone' op-amp power amplifier to pair with the Mr. E.Z. Tube.

Power transformer - The vast majority of tube amps use a transformer connected to mains power (AC) and a rectifier circuit to produce clean high voltage DC for the tube. This heavy chunk of metal and wire is expensive and dangerous. The rectifier diodes and capacitors alone are a whole project. Mr. E.Z. Tube uses a 240 volt switch mode power supply I originally designed for nixie tubes. The SMPS is simple, with the option of battery operation!

For a detailed overview of the SMPS operation see my SMPS instructable for nixie tubes:


The Mr. E.Z. Tube SMPS has a few enhancements to eliminate switching noise:

1.A larger inductor (1.2 amp continuous rating).
2.A soft recovery rectifier diode (BYV 26C) was used.
3.Two large output capacitors and a choke were added to the HV output.
4.Updated firmware with high voltage 'enable' switch.

With these enhancements there is VERY LITTLE switching noise - it is only noticeable with no audio playing and power amplifier volume at 100%.

Step 2: The Tube

Mr. E.Z. Tube will take any tube with a pinout similar to the ECC81/ECC82 (12AT7/12AU7). These tubes are quite popular and common. Tubes are available as 'new old stock' and new tubes manufactured in China and eastern Europe. I have only tested an ECC82, but I look forward to trying other types.

There are a ton of tutorials on correctly biasing vacuum tubes. I followed the suggestions here:


My output coupling capacitors are a bit large (1uF/250V), I plan to try the recommended 0.1uF caps soon. Thats the beauty of the Mr. E.Z. Tube development board - swap parts and hear the difference for yourself, no hype.

Step 3: The Interface:

What's an amplifier without a remote control? Mr. E.Z. Tube has an IR remote interface powered by a PIC 16F628A. The pic decodes IR remote commands in the RC5 format. Codes are programmed by shorting the jumper connected to RB0 on the pic. The front lights will prompt for codes (with a blink) in the following order: power, volume up, volume down, mute, source-select/auxillery one.

Volume is adjusted with a DS1807 I2C audio potentiometer. I have not received this chip, so this functionality has yet to be implemented in the beta control firmware.

The PIC is programmed with a staggered startup and shutdown routine - a FET is used to power the tube heater/filament several seconds before the high voltage supply is enabled. This is supposedly good for tubes. The heater is run from 5v, also for better life (be sure and put a heat sink on the 7805). Heater control gives Mr. E.Z. Tube a true remote controlled 'power off'.

4 leds on the front panel indicate status. LEDs show, from left to right: system power, filament/heater power, high voltage supply, low voltage supply (for future use with a gainclone power amp).

Four auxiliary outputs are brought to header pins on the left side of the PCB. These can be used for anything, but I intend to use them as follows:
AUX1: low voltage SMPS enable for a future gainclone power amplifier (next month's instructable).
AUX2: button to trigger remote control code programming (already set).
AUX3: digital/analog source select for a (very) future SPDIF DAC.
AUX4: unassigned.

FIRMWARE NOTES: this is a beta firmware version. I will release an update here when I receive the DS1807. The IR decoding routine isn't the best. It samples according to the RC5 protocol - but I don't know if thats what my remote uses. Codes are stored in the PIC EEPROM so you can see what they look like by reading them out with a PIC programmer. If you need a cheap easy programmer try my enhanced JDM2, also available here at instructables:


My Happauge WinTV remote works well, but I can see in the EEPROM that I'm not getting the bit stream correctly. None the less, by identifying the 1's and 0's, and noting the errors (with $FF), I get pretty reliable results. This will be fixed when I get a remote that I KNOW uses RC5 (I have no idea what the Happauge remote puts out...).

Step 4: Files

This ZIP archive contains all the files for the current version of Mr. E.Z. Tube, including the PCB:

Circuit and PCB: Cadsoft Eagle format - made with the freeware version.
SMPS & Interface firmware - written with the freeware version of MikroBasic.
OO.org documents - this instructable in the .odt format (no more MS Office exports).

Interface firmware is still in beta. A final version will be released when I recieve the DS1807 potentiometer chip.

The file was missing for about five minutes. Its there now!
I'm confused. Is this an amplifier made out of an old vacuum cleaner?
No my good friend, Vacuum tubes are transistor-like devices that were made before the advent of silicon-based components. See that big light-bulb-looking thing? That's a vacuum tube. It does the same thing that a transistor does, only less efficiently... Audiophiles say that they are better at amplifying because they are able to do so analog-ly, which leads to a truer sound.
kind of the opposite...they are non linear devices, which provide mild and (generally agreed upon) musical distortion. Also, when pushed into distortion (a solid state circuit can also be pushed into distortion) they do so more gracefully then solid state. Hence their popularity in guitar amps. To this day solid state tube modeling cannot achieve the same mmm good tube tone. Also worth noting (as the author states) is that tis setup is less than ideal for audio. Much of the tone of a tube amp comes from your trannies. Bad transformer (or none at all), most likely bad tone.
I could be wrong, but I believe two of the most linear devices made were/are the WE 300B power triode and the 6SN7 small signal dual triode.
as an audiophile, i can say everyone knows tubes make for a nice warmer sound
While the sound may be nicer and very 'warm', it also contains many more harmonics and much more 'static' noise. Oddly enough, these two things, which purists would consider vile, are considered to be pleasing by most people.
I'm not an audiophile, as listening to a stream-rip download of a 96kbps stream through a mono output with factory earbuds (yeah, the little black ones... you know what I'm talking about) is a satisfactory listening experience for me. But I have heard a tube-based amp compared to a "newer" one, and there definitely is a difference.
man you just got me all warmed up for a good time with this reply.
Oh goodness...
too much guac on my burrito.
Allways amusing to follow discussions about quality of tube sound and the comparison between tubes and silicon devices ... I simply use both of them, build amps either way and like them both. Clearly there are differences, but not only between tubes and silicons ... but between all amplifiers. Don't discuss the WHY. Why do people smoke? They simply like smoking.
I guess you could pull a "the awesome sound is addictive and we can't live with anything else..." argument, but I think the comparison is a bit unfair... o_O
I'm not so sure 'bout that. I mean, almost any aspect of music would be harder for me to quit than my smoking...
When electronic amplifiers were first marketed, some people said that they could never reproduce sound as accurately as an acoustic phonograph.
erm, no sorry PC it is about making an amplifire out of vacume TUBES such as the ones found in the first radio's and such.
<p> &quot;Standard warnings apply: Mr. E.Z. Tube will not hesitate to kill you given the chance. &quot;<br> <br> Do not taunt Mr. E.Z. Tube!<br> <br> (search youtube for 'Happy Fun Ball&quot; to get the reference to old SNL commercial)<br> <br> Great project!3</p>
Do these tubes glow?
How much will it cost?
How do I power it with a battery?
What remotes can I use?
Sorry, forgot to put this on my last comment. Do you have any tube suppliers that you'd reccomend? Nixie tubes too (that's my next project :D ). Thanks a lot!
We actually have a store that sells lots of tube in the Netherlands. That is where I bought mine. I think there are 2 big tube suppliers on the internet (us suppliers). One seems to have less hype and better prices. Nixies: ebay usually.
thetubestore.com and tubedepot.com show up in the google ads for this instructable. :)
Hah, didn't even think to look at ads. Thanks!
also try vacuumtubes.net, they boast about having the lowest prices and will beat or match competitors.
NIce work, but how about noise from the power supply? Isn't there any high frequency hissing if no audio signal is feed into the circuit? Btw. I like it that you combine the tube with some microprocessor. I think that a amp build with a tube should also be as comfortable as modern transistor amps ...
For the past 35 years, I've been design/building vacuum tube based audio amplifiers and all sorts of tube audio gear for recording studios, esoteric home stereo systems, a few car systems (yes, tube amps for cars! people always find that remarkable for some reason?), and lots of non-audio vacuum tube based applications. I am so lacking in the area of digital electrons! This project just may be what I need to break on through to the digital side. I do believe that electrons-in-a-vacuum can co-exist with electrons on silicon. I can't remember how long it's been since I've said "I'm glad I found this site", other then when I clicked on this link. Very hip and an excellent presentation! Peace, DrRick PS: Does anyone want to collaborate on a vacuum tube home CD player? The concept is to use a high quality computer CD drive, pick up the audio right at the D/A converter and feed it through a tube based audio stage (or two if needed) instead of the conventional chip based opamps.Many of the D/A chips are current output (as opposed to voltage output), so we ca use a resistor as an I/V converter or better yet, a transformer. We can probably skip the complex low pass filters typically used because the transformer (unless we use an expensive one-I prefer free) frequency response should cause it to function as a LP filter. I can handle the audio circuit design and the power supply design. We can use a linear supply and avoid the noise from the typical computer switch mode supply. What I can't do is design some sort of controller to make the drive play, skip tracks, etc and the display for it. Any one up for it? There are other cool things that can be optional, like breaking down the drive and making it top load, perhaps in a cabinet about the size of a turntable. Maybe some can design the display using Nixie Tubes, or, even more cool, a CRT (oscilloscope / picture tube) as a display that can be switched to function as an audio scope.
im down
Do you got a Hauppauge TV-Card? I got the same remote to mine. Great device
ADDED: final picture and firmware update.<br/><br/>I got the DS1807 digi-pot today. In finished the tube control firmware.<br/><br/>ALSO: SMPS firmware upgraded - several major problems:<br/>1)Disable often left the PWM running without control = BAD BAD BAD<br/>2)In-rush at startup caused system wide brown-out from a cold start (also if the unit had been off for a while)<br/><br/>FIXES:<br/>1)PWM now totally disabled if the ENABLE pin is low.<br/>2)Added voltage ramp-up for all starts using timer0 module.<br/><br/>Source select is still un-implemented (no sources to select yet...)<br/>
This is an awesome tutorial. I can't wait to build one!
Cool, I hope you like it. Post a picture in the comments when you finish! Cheers, Ian

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