• One small tips for low voltage heater tube

    kodera2ta day ago 0 comments

    I got a question regarding IV-15 heater voltage in hackaday messaging system. The questioner burns out more than 10 tubes of IV-15 and asked me how I use. The answer may be useful for all (except for vacuum tube expert), and would like to show,

    The instance of power on, the resistance of heater is quite low (proportion to temparature)  and if you simply apply the rated voltage, for example 1.0 V, it will burn out. The remedy is quite simple and was a common sense in 60 years ago of vacuum tube era, "insert tens ohm (for example 20 ohm) in series to heater and apply the rated voltage."

    Reading battery-driven vacuum tube circuit, especially lower (< 3 V) heater voltage tube circuit on article and books, we can find "R" in series to heater. Especially low voltage heater tube has a low ohmic value for enough current flow by the rated voltage, so they are more fragile than 6V or 12V or higher voltage heater tube. In the vacuum tube, plate and grid are separated and very strong to voltage application (they are separated and basically no current flow if heater is not ready..), BUT in the all of vacuum tube, heater are, naturally, connected and ready to over-current. Actually heater is weak point of vacuum tube.

  • Practical VFD-triode based power amplifier

    kodera2t3 days ago 0 comments

    As presented in the previous log, yes, VFD which has triode structure works perfectly for audio application! This time I just swapped this triode (VFD) with Nutube in my class-D power amplifier. Indeed, the sound is super wonderful, and as above picture, now it becomes my main power amplifier!!!!!!!!!

    Actual operation is presented in the movie below, please check it!

  • Various vacuum tube to be explored

    kodera2t4 days ago 4 comments

    I got several interesting vacuum tube. My policy to buy tube is,

    • Less than $10 per tube. I am not high-end audio maniac, and also not so rich.
    • Should be something unusual and looks interesting

    This time, the first Geiger-Müller tube is exceptionally expensive (but $20).

    It is Russian tube, and I will make Geiger counter someday...

    Second one is just a 7-segment VFD. Can we make 7-channel audio amplifier (if ignoring channel isolation)?

    Third one is historical "Acorn" made in 1944. We can find lots of VHF and UHF circuit examples. I hope I will make super-regenerative receiver...

    Fourth ones are 6D-HH13, dual triode in the last era of vacuum tube made by Toshiba. It has a longer Nuvistor shape, and was utilized in VHF amplifier..

    The last one is 5672, a power pentode by Raytheon in 1952. All of them are around 500-800JPY in Japan. So still lots of vacuum tube is available, and I guess LPC810 will be available for coming tens years..?

  • How to start vacuum tube experience on breadboard?

    kodera2t4 days ago 0 comments

    Today I will show how to start your vacuum tube experience on solder less breadboard.

    This is the objective circuit of today. It is reflex single tube radio and quite simple but shows very high sensitivity (and not so unstable as regenerative receiver..) Let's start now!

    First of all, let's solder the wires to vacuum tube socket. Except of subminiature tube, vacuum tube requires "socket" (originated in incandescent lamp..). For breadboard connection, let's solder the wires to the pins. Some of vacuum tube as NC pin or overlapping pin, so not always we don't need every pins soldered.

    This is the completed one. 2P2(3S4) has 2-6 pin overlapping and also #5 is the heater center point and this time we don't need to solder 2 and 5 pins.

    And now let's solder the battery connector as above. Please keep "red" to +. and...

    Now let's start charging Ni-MH battery during preparation by connecting connector with power supply PCB. When charging is done, on-board LED will turns to Green.

    In the same manner, let's solder "jumper wires" to (1) variable capacitor, (2) ferrite bar antenna, (3) ceramic earphone, as above.. Now the soldering works are done.

    Now let's again see the schematic and wires all components on the solder less breadboard. If the connection is well, actual layout does not matter for the operation.

    And now let's plug vacuum tube to the socket. I recommend to do it before connecting to breadboard....

    And let's connect all of the components, variable capacitor, ferrite bar, ceramic earphone and vacuum tube. At this time, please check short circuit between HV (+30 V line to GND). It should not be connected and if connected, power supply PCB may be destroyed.

    And finally let's connect breadboard to the power supply!

    The moment of truth...... by changing tuning capacitor you will hear AM stations with very loud volume! 

    For those who may not find all of parts, I will release parts kit on indie soon. Enjoy vacuum tube experience!!

    and this kit will be released at my tindie store by $42. Stay tuned!!

  • Russian VFD works triode?,,, naturally...?

    kodera2t6 days ago 2 comments

    So as reported in the yesterday's log, I got VFD which structure is actually triode. So I simply swapped it with Nutube in my high-resolution audio DAC.

    The moment of truth...... please see the following video.

  • Mysterious item from Ukraine..

    kodera2t06/12/2019 at 12:33 1 comment

    I got a mysterious item from Ukraine. It looks like subminiature tube but rather it is VFD.

    The name of it is IV-15 and it seems it is compatible with DM-160. The data sheet says,

    just a few months ago, this symbol was mysterious symbol but now I can understand. It is direct-heated TRIODE. Indeed I can find several people who realized amplifier by this VFD, and it seems not difficult. I will measure its frequency response and check if "VFD radio" is feasible or not. (As for Nutube, its transition frequency is less than 1MHz and impossible to make radio (except for LW radio))....

  • Quick update: full sub-miniature tube superheterodyne radio

    kodera2t06/11/2019 at 12:06 0 comments

    This time I got a heptode subminiature tube, 2G21. I guess this tube was widely used in 50's and 60's ? Vacuum tube era pocket radio. I've used MT tube 1R5 heptode and this time I simply swapped it with 2G21, without any parameter modification.

    One additional note: Resistor between plate of triode (#3) and GND should be set for 150k (1R5 was 100k), otherwise local oscillator will cease in a few minutes..

    As shown in the image, now the radio is fully made by subminiature tube. You may notice two variable capacitor for the radio... YES, the double variable capacitor certainly change both receiving resonator and local oscillator resonator but my ferrite bar antenna does not resonate where I need if I use double variable capacitor. Thus I used independent variable capacitor for receiving resonator. (I have to double tune for local oscillator and receiving resonator, but it is working..) Actual operation can be found in the following movie.. have fun!

  • LED blinker circuit (non-stable vibrator)

    kodera2t06/09/2019 at 10:02 0 comments

    As per some request, I will show the circuit of LED blinker.

    The pairs of C3, R6 and C5, R5 defines the time constant and that defines blinking frequency. 

  • Usable (I would not say practical) superheterodyne circuit is fixed...

    kodera2t06/09/2019 at 09:49 0 comments

    Before I presented the superheterodyne type but this time I've fixed for more usable shape. I've wanted "direct speaker drive" (withOUT transistor active speaker) to enjoy "pure vacuum tube sound" but three battery driven tubes were not enough to do it (or my design is not so good.)

    So this time I simply added audio amplifier at the end of circuit.

    This the the whole circuit. Indeed, super simple compared to my 48kHz USB DAC, but works very cleverly. The first tube (left end) is 1R5 heptode working as local oscillator and frequency mixing. The oscillator coil is the one for transistor circuit (Red coil). After passing 1R5, 455kHz signal goes to 6418 subminiature tube amplifier, and goes to reflex circuit, which demodulate 455 kHz AM signal to audio, and finally the last tube is simply audio amplifier and goes to speaker through impedance trans. Actual operation is as follows. Indeed, it does not still exhibits so high-sensitivity but anyway speaker driving pure vacuum tube superheterodyne radio is done!

  • Most useless application? LED blinking by 3A5

    kodera2t06/08/2019 at 12:17 2 comments

    I like 3A5 so much, for its mellow and brilliant sound through triode. But this time, the application may be most useless one. It's LED blinking. 

    It's blinking period can be determined by C-R discharging time constant. Indeed, we can simply regard Grid-Gate, Plate-Drain, and Kathode(3A5 is direct heated tube so it is GND of heater)-Source between vacuum tube and FET. The big difference is heater power requirement and high voltage requirement. Actually "gm" is common in both FET and vacuum tube!