• Photomultiplier experiment

    kodera2t2 days ago 0 comments

    Eventually the tube is getting the present age. The tube is "photomultiplier", which is famous for the high-sensitive photon detector in Super Kamiokande (detect micro-weak light from Cherenkov radiation in a big water pool.) The tube requires high voltage, ideally 1000V for higher gain, but I know how it is dangerous. So this time I made 4x voltage rectifier for AC100, which can generates around 560V DC.

    The tube is IP28, which has 9-stage photo multiplier, so 553V/9=61V is applied for each stage. Voltage divider is just series ohmic resistor as shown in the picture below.

    The circuit is quite primitive but I confirmed its operation as very initial experiment as shown in the movie below. The next step will be radiation detection (I hope it will work as Geiger counter..) together with proper scintillator...

  • Tiny audio power amplifier

    kodera2t3 days ago 0 comments

    Recently I tackled with bigger tubes but now I have a quick return to sub-miniature tube.

    It is quite simple amplifier by 5672 with output transformer (for transistor). It still requires 30V so I power-on with my previous making (3.7V to heater, B voltage generator board). Actual operation can be found in the following movie. Have fun!

  • Dekatron, a counting vacuum tube!

    kodera2t5 days ago 7 comments

    Indeed I've already got this unique tube before but till now I did not touch this tube. The neck was its special pinout. Indeed I don't have 13-pin vacuum tube socket, so this time I made it by 3D printing.

    The circuit inside enclosure is quite simple, purely consisting of C, R, and diode. The plate voltage is generated by triple voltage rectifying and from AC 100V. (leading around 400V DC). For its light rotating, the tube requires two phase clock, same as rotary encoder. The current circuit generating 50 Hz two phase clock by just R-C phase shifter. This dekatron supports bi-directional rotation, so I added SPDT switch for phase capacitor for forward and reverse (CW, and CCW) rotation.

    But maybe DEKATRON is the only one DIGITAL vacuum tube in the history. It is not just display like Nixie and VFD, but works as digital counter and memory and display.

    Actual opration can be found in the following movie.... 

    As you can watch the spinning color in the video, the color of A102 is not orange but blue-violet, meaning filling gas is not neon but argon or something else neon.

  • Geiger-Müller tube experiment

    kodera2t6 days ago 0 comments

    This time I will try "Geiger-Müller" tube. It is a special tube for the detection of ionizing radiation, and requires high voltage around 400V. For this voltage requirement, I just use a parts kit of voltage booster and checked its operation. It is not so showy but I confirmed my place is safe ;-)

  • Secret to overcome "crazy howling" of 7-seg VFD.

    kodera2t7 days ago 2 comments

    I know 7-seg VFD is NOT for audio amplifier but digit display, and I am rather "crazy", but eventually I overcome "crazy howling" issue. Without any trick, triode operation 7-seg VFD will cry and howl up to maximum its output. Unless your house is like " Little house on the Prairie", your neighbour will get angry for continuous noisy howling.

    What's the trick? It is indeed conventional way to stabilize howling of direct-heated tube, putting magnet on the tube.

    The picture above shows the actual way to reduce howling. It is quite "size and position sensitive" and bigger magnet will kill its amplification, and smaller one will not have any effect for it. Anyway I found the way!

  • 1930's classic ST tube plays wonderful stereo sound!

    kodera2t07/16/2019 at 09:28 0 comments

    Previously I've presented mono power amplifier using classic ST tube, type 19. Indeed I was so fascinated its wonderful sound (far wonderful than I expected), and this time I made two channel, stereo power amplifier. Basically the circuit is the same as before, just repeating twice. Its heater voltage is generated by switching regulator (tiny AC/DC adaptor), and plate voltage is generated just rectifying AC100V. So no power transformer but just one choke coil. You can see the rest 4-transformers, the input trans is BOGEN T725 between white-violet-black and violet is used for centre tap for tubes. The output trans is tiny 0-7-12k to 8 ohm, it is apparently not centre tap but it is working. (not ideal operation, but working well).

    Actual operation can be found in the following movie... Have fun!

  • Klystron is working!

    kodera2t07/11/2019 at 09:22 0 comments

    This is the first trial for me to get microwave oscillation of Klystron. The klystron tube requires three voltage, heater, resonator, and reflector. Heater voltage is simply generated by switching AC/DC, and -105V reflector voltage is generated by VR105-MT voltage regulator tube (in the following movie, I am saying -75 V, but the correct one is -105V DC) through just rectifying AC100V to DC, and resonator voltage is generated by external DC power supply. As you see, YES it is working!

  • I gave up 7-seg VFD but completed by another VFD!

    kodera2t07/10/2019 at 12:02 1 comment

    As presented in my previous log, I've tried audio amplifier implementation, and after prototyping I moved to "tiny production" for tindie. HOWEVER, tight soldering to PCB (prototyping stage, it was tentative) leads to un-solvable ultra strong microphonic making ultra loud howling through speaker-tube feedback. I've tried several material attachment to VFD to reduce feedback, but sometimes it is succeeded but another day it goes super howling. Eventually I gave up this game. The 7-seg VFD does not have any responsibility because they are made for "digit display". Fortunately I have another VFD display, DM160. It is not segment one but its "audio application" is far stable and reliable, and also characteristic variation is very small between devices. So I changed tube from 7-seg to DM160.

    Actual operation is presented in the following movie. One additional function of this new amplifier is "power-on speaker pop canceling". You will see "zero pop" for power on in the following movie..

  • 7-seg VFD based audio amplifier is done!

    kodera2t07/06/2019 at 11:40 1 comment

    As presented before, I've confirmed 7-seg VFD can work as triode for audio application. But the previous case was just prototyping and indeed PCB was the one of Nutube.

    This time I designed a PCB especially for VFD. It looks like showing some digit but it does not but amplify the audio signal for left and right channel.

    However, I encounter ultra strong howling, consisting of feedback loop from speaker to microphonic. Therefore I have to put "soundproof sponge" on VFD in order to cut this troublesome feedback. By putting this sponge, howling can be suspended, but the looks is not so good (something black item on PCB...)

    Actual operation can be found in the following movie...

    And after taking movie, I completed the fix by de-activate three segment of VFD as the image below. The issue is too much gain of VFD (can you believe VFD has too much gain?, but true..).

  • Small update for Klystron

    kodera2t07/06/2019 at 11:15 0 comments

    As my personal interest, I want to oscillate the klystron. Definitely I need socket for experiment, but its socket is quite rare (it is natural since no one use such a small size klystron nowadays.). So this time I made socket by octal-GT tube socket.

    Just socket is still fragile for experiment, so also its stand is made by 3D printer.

    Just a little step forward now...