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I've made more modifications to my bodacious amplifier. First of all, I added tremolo, using a 12AX7. One triode is the PLL (that's Phase-locked loop, if you MUST know), and the other serves as a buffer. The big question was how to interface it with my existing circuitry. Well, it turns out that it couldn't be done. Just kidding! I had to use an optoisolator. Of course, it had to be able to handle high voltages and whatnot. So, I wound up making one with a neon lamp and a cadmium sulfide photocell in a piece of heat shrink tubing. The photocell will vary it's resistance changing the bias voltage on the 6L6 tube. Boom! Sweet sounding tremolo!

I also added an EM80 magic eye tube that serves as the VU meter. It's not really practical, but it sure looks cool! It was pretty easy to incorporate it into my circuit. It gets its signal from the plate of the 6L6, going through a capacitor and a 100k potentiometer to adjust the sensitivity.

Last, but not least, I added reverb, which was the final thing that I wanted to add to this amp. That took a while, and required two more 12AX7s tubes to be added to the amp! That puts my tube count up to 7! So anyway, the reverb tank, one that I stole out of the amplifier that I'm now using as a speaker cabinet for Killovolt I, had issues of horribleness. The impedances, while correct for the solid-state amp, were all out of whack for my tube amp. My amp doesn't care much about the output impedance, but it does care about the input impedance! So, I rewound one of the coils, and it worked! I soon realized that that reverb tank sucked, so I bought a MOD something or other that already had the correct impedances. It sounds very '60s, but I will say that the best way I can describe it is that it sounds boingy... But anyway, now my amp has reverb.

Those are the last things that I'm going to add to this amp. Besides, there's no more room inside it!

Current Location: Negatory
Current Mood: Existing
Current Music: Rumble by Link Wray

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So here is the amplifier that I've been working on since my last post. As of this point, it has effectively been completed. Now there have been a couple changes (actually, a LOT of changes) in the design since my last post. For the main high-voltage transformer, I had used a microwave oven transformer, and microwave oven capacitors during testing. I had measured about 3.2Kv on the plate. But alas, that transformer had problems with going into saturation... It was drawing 10 amps out of the wall with no load! And it soon melted... But I was not about to give up! I rewound a big 12vac 420VA transformer I had lying around. I took off the secondary but left the primary. I wound it with just over 1,000 feet of high-temp 28 gauge magnet wire, then impregnated it with shellac. After rewinding, it put out 1250vac, which comes out to around 1700 volts after going through a full-wave bridge rectifier, made of several 1n4007's and potted in a plastic container. Now that's not as exciting as 3+ kilovolts on the plate, but it certainly is easier to find parts for it! I stuck with the microwave oven capacitors for a while, but they just didn't have enough capacitance, so the thing hummed like crazy. How uncool. I also used a huge-ass inductor in this power supply to help. I made this one using a smaller microwave oven transformer that I completely took apart, rewound, and then potted. I got and inductance of nearly 30 Henries out of it! I even high-pot tested this bad boy up to 5 kilovolts with no problems! Now back to capacitors. I got hold of an 8uf 1500vdc oil cap, as well as many more microwave oven capacitors. They helped, but still didn't hold enough juice. Finally, I got 10 450v 100uf electrolytic caps. I hooked five and five in series with balancing resistors. That put me safely up to around 20uf/20uf at 2 kilovolts. Humming solved! For the high voltage wire I tried to buy actual high voltage wire, but it was just too expensive, so I used 22 gauge 600 volt rated stranded wire. Now you might be saying that that's not going to handle almost 2 kilovolts. Well, you're right. I went down to my local pet store and purchased about 8 feet of silicone tubing meant for air supplies for aquariums. I just cut it to length and slid it over all the wires that carry high voltage, and BOOM! Instant high-voltage wire! For safety, there is a 250Vdc analog panel meter on the front panel to tell you the plate voltage. Kilovolt panel meters are expensive, so I one that was 1/10 of the voltage rating I needed, and then used a resistor network so the meter reads 1/10 of the actual plate voltage. That thing's accurate to 2%!

As for the output transformer, I used a modified microwave oven transformer, with the windings manipulated to put about 7200 ohms impedance on the plate of the 4-250a with and 8 ohm speaker. Believe it or not, it has an awesome sound with some serious fidelity! So when I had put this amp in an aluminum enclosure, it worked fine for quite a while. Suddenly, BANG! Nearly 2,000 volts arced across the winding to the frame in that transformer! What a sight! After repairing that tranny, I isolated it from the case with several sheets of acrylic and held it down with nylon screws.

For the filament of the 4-250a, the one that draws 5 volts at 14.5 amps, I completely rewound that microwave oven transformer that I had originally used for the high voltage power supply. I used lots of turns of 20 gauge wire for the primary, and I think it was about 6 or 7 turns of 10 gauge wire for the secondary. That thing can crank out 5 volts at 30 amps easily! Also, I have a hum balance pot and stuff so I didn't have to make some sort of monster rectifier/capacitor to put clean DC on the filament.

Now for the other stuff. Instead of a EL43 or 7591 driver tube, I went with a good ol' 6L6. I use an audio interstage transformer to couple it to the 4-250a. For this tranny, I had wound one using the core of a large wall plug transformer, but the windings shorted out partially. It still worked, but poorly. I wound another one. The primary shorted out to the secondary! This seemed like the end. What was I going to do? I purchased a powdered iron core meant for a 1000 watt switching power supply. Now powdered iron has pretty low permeability, so it's hard to get the right amount of inductance for bass frequencies on the primary for the driver tube. On the other hand, powdered iron cores have great saturation characteristics, and incredible high-frequency capability. But this core was so big that I wound over 1,200 turns of 30 gauge wire for the primary, giving me an inductance of around 15 henries, if I did my mathifications correctly. That gave me a DC resistance of 30 ohms for the primary! Oh, and I put in a 40% tap for the screen of the 6L6. I wound the secondary with about 3,000 turns of 34 gauge wire, which gave me the 1:2.5-ish ratio I was looking for. I bench tested this tranny, and it had a FLAT frequency response from 10Hz to 100,000Hz and beyond! Not to mention some seriously low distortion to boot!

I know I said that I was going to use a 12AX7 for the first and second preamp stage, but I wound up going with a 6SN7 instead. Again, it's a dual triode with some radical curves like the 12AX7, but with a lower gain and higher plate current. Basically, I had two 6SN7's lying around, but no 12AX7's, so that's why I used it. Now there are two audio inputs hooked into this tube. There is one for the second triode, or preamp stage, and one for the first triode, or the pre-preamp stage. Basically, it's my high-level and low-level inputs. In guitar terminology, the high-level is the "clean" channel, and the low-level is the "overdrive" channel. And of course there is a switch to select which input you want to use, so that the triodes are coupled correctly depending on which input you want to use. I also made an adapter out of an old tube base so you can use the awesome 12AX7 in place of the 6SN7. That gives you higher gain and more crunchy distortion, depending on what type of music that you want to want to play. The interesting thing is that the volume control is hooked up AFTER the last preamp stage, going into the 6L6. You might think I'm crazy, right? You guessed it. But putting the volume control there allows the player to play in insane overdrive or whatever, while being able to turn the output volume way down so the neighbors don't get too pissed.

For the power supply for these tubes, there is one transformer. Again, I, being incredible amazing, wound this one myself from another transformer I had lying around. This one was rated for 14vac at around 350VA. For some crazy and illogical reason, I decided to rewind the primary as well, even though I could have left the old one and used it... Anyway, this thing has more windings than, well, something that has a lot of windings. First is the primary. Many turns of 21 gauge, wire, blah, blah, blah. The 1st secondary winding is a 11vac winding capable of up to 15 amps with a tap at 6.3 volts for the filaments of the 6L6 and 6SN7. So you might be wondering what I am going to do with 11 volts AC? It gets rectified and then powers the fans in the case! DUH! I wound the next winding with 200 turns of 34 gauge wire, giving me about 100vac. This gets rectified, and supplies the -140 volt bias voltage for the 4-250a. It goes to a 100K pot on the front panel so you can adjust it from -140 to 0 volts. There is also a milliammeter so you can see how much power is going into the plate. It also supplies the bias voltage for both triodes of the 6SN7. The 6L6, although set up to use fixed bias, is using cathode bias at this point. The next winding was wound with 500 turns of 30 gauge wire and supplies 250vac. Again, this gets rectified, goes through some capacitors, and gives me about 350vdc for the plates of the 6L6 and 6SN7. The last winding has something like 850 turns of 34 gauge wire. That puts out about 420vac, which, you guessed it, gets rectified! Who would have thought? That gives me nearly 600vdc for the screen of the 4-250a. In case you were wondering, I can't run that tube in either ultralinear or triode mode. The screen is designed to run at, and no more than, 600 volts. If I were to strap it to a tap in the output transformer, or strap it to the plate, there would be just too much voltage for the screen. Also, there is a pushbutton to apply high-voltage to the plates after the tubes have warmed up.

So how did this amp sound? Quite honestly, terribly. But I hadn't gotten the thing dialed in yet! First of all, it was motorboating. You know, going putt-putt-putt really loudly. So I decoupled both the preamp and pre-preamp stage. 5.6K resistor, 30uf cap, 5.6K resistor, 30uf cap. Problem solved. Then it sounded great in the clean stage, but terrible in the overdrive stage. If you turned the volume up at all, it would start to squeal insanely loudly. Sounds like some sort of feedback was happening, huh? I put a Dr. Pepper brand tube shield over the 6SN7, which helped with the squealing, but it still sounded awful. There was lots of noise and buzzing, and no where near as much gain as their should have been. I've tried different tubes, changing the anode resistors, changing/adding grid stoppers, changing bias, coupling caps, etc. I also redressed all the wires so that any wire that carried any audio signal was shielded. Originally, I was going to run the ground completely isolated from mains and stuff. There was serious noise then. I soon realized that that was a safety issue. So put in a three-pronged plug so the chassis and circuit were earth-grounded. That helped with the noise, but not a whole lot. I tried running a dedicated ground TO EARTH, the amplifier's own metal stake in the ground. No difference. I though I was just going to have to live with a crappy overdrive input. I went into a deep, spiraling depression... All hope was lost... Okay, okay. So I'm being overdramatic. Finally, in desperation, I put just a little bit of negative feedback on the overdrive stage. Just a 220pf cap connected from the anode to the grid. That amp came to life! No more squealing, with or without the tube shield, though the shield did help with ambient noise. The amount of noise and buzzing dropped tenfold. Finally, my amp had that classic tube sound that I so wanted! It has some sweet overdrive, and a smooth, classic tone.

After all that crazy stuff, Killovolt I has effectively been completed. I can't stop playing on it! I don't play guitar, but I had to go out and buy one just so I could fool around with the thing! I measured the output, and put it out 50 cleans watts RMS into 8 ohms. I'm pretty sure my "high-end" audio output tranny was the limiting factor. My measurements show that more than 75 watts was going into it, and 50 watts were coming out. Hmm... sounds like I've got some leakage inductance... Also, the waveform on my 'scope seemed to indicate that the amp itself wasn't clipping after 50 watts, but the output tranny was going into saturation. So that tranny is the limiting factor! When I get some money, I'm going to put a decent one in and see what happens!

So what is Killovolt II going to be like? I think I'll have to make it a class AB2 with two 4-250a's just for fun. According to the datasheet, I can pull just over 1000 watts out of two of those tubes!

Oh yeah. Here're some pictures for ye all.

Here's the interstage tranny and the output tranny.

With no tubes. Notice the ceramic socket for the 4-250a. The big holes in it are for forced-air cooling.

This shows inside the case from the front. You can see the 1250vac transformer, and the power supply inductor in front of it. The small transformer with the blue tape just puts out a 12vac signal to tell the fans to turn on.

Here you can see the 4-250a filament transformer in the back, and the power relay that controls plate voltages and stuff in front of it.

Here is the power supply board for the bias, 6L6 and 6SN7 plate voltages, and screen voltage. The power transformer for it is behind the board, but you can't see it in this picture. That's what that molex connector hooks up to. That blue capacitor is for the fans.

So yeah, this thing weighs about 80 pounds... If you've actually read through all of this, congratulations! Click the link below for your prize!


Current Location: Somewhere
Current Mood: nerdy
Current Music: Rock!

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Check out what I have finally obtained!!!

This is the Eimac 4-250a tube. It is a power tetrode mainly used for radio frequency stuff. Yes, it is the same tube as the one in my icon. This picture was obtained from le internet, and is not the exact one that I have (actually, I have two).

So what am I going to do with this thing, you might ask? First of all, let me state that I do not do anything with RF transmitting and Ham radio stuff, EVER. I like audio. That's right, this tube is going in a super guitar amplifier! My goal of this project is to make an amp with a purely unique sound, and lots of juicy tube power!

**If you are faint-hearted, or just not electronically savvy, then take caution in proceeding in the next section. It contains lots of technical stuff...**

Now on to the design. This beast of an amp is going to be a single-ended grid-biased (at least on the 4-250a) amp. That should give it quite a unique tone. Also, how often do you see a single-ended amp capable of 100+ watts of power? This is the overall basic design.

Time for details! I'm going to start from the input out. The first tube is going to be a 12AX7, which is, in my opinion, the best audio tube ever made. I don't think it gets enough respect since it usually resides in the preamp section and is not one of the big, flashy output tubes. The filament is going to be wired for 6 volts using the convenient center-tap. The 12AX7 will boost the signal enough to power either a 7591, or an EL34 (I try to use current production tubes whenever possible). Since either one uses a 6 volt filament, I can run it in series with the 12AX7. This tube will then deliver enough power to drive the grid of the 4-250a. As for this tube, I have not yet decided if I will run it in an ultra-linear configuration or not. I'll probably try both to see what sound I like best.

Now for one of the most crucial parts of any tube amp: The output transformer. No one makes a transformer that can handle the high voltage, current, and impedance of the 4-250a. BUT DO NOT ABANDON HOPE ALL YE WHO ENTER! There are options. OPTIONS! I can have someone custom wind one for me. That is probably going to cost a pretty penny, or several pretty Ben Franklins, for that matter. Another choice is to custom wind one myself. I have already done so, but the 40 awg wire I used for the primary is really too thin to crank the 4-250a at anywhere NEAR full voltage, but it's fine for the low voltages I've been testing the tube at. I could always rewind it again.I stumbled across another transformer. It turns out that a microwave oven transformer, having undergone some slight and easy modification to the primary winding (now the secondary in the amp), has the EXACT right impedance ratios to drive an 8-ohm speaker! Fortunately, I have two of these things lying around. With a 1000 watt rating at 2100 VAC (>3500 VDC), this thing can easily handle the 4-250a. Granted it is not audiophile quality, it will certainly work for full power testing until I can obtain a more audio grade replacement. Who knows? Maybe it willhave a great tone! I'm shooting for tone here, not quality!

So that's how the audio signals work. Now that's all fine and dandy, but I have to feed these tubes plenty of nutritious and clean power. This amp is going to have four or different power supplies. The first one is just a 6VAC transformer to power the filaments of the 12AX7 and 7591 or EL34. No big deal. Next, we need to power the filament of the 4-250a. While the 12AX7 and 7591 or EL34 will draw about 2 amps combined, the 4-250a's filament sucks a little over 14 amps at 5 volts! That's 70 freaking watts! I'd be happy to have just that in audio output! More than likely I'll buy a regulated switching supply for it. Sure I can use a big-ass transformer in a linear power supply to do the job, but why bother when I can buy a switching supply that can handle it for 30 bucks? Let's not reinvent the wheel here... unless I have to!

The next two power supplies will be for the plate voltages. For the smaller tubes, a 250 VAC transformer (more than likely it will have a 6 volt filament winding so I don't have to use a separate transformer), a full wave bridge rectifier using semiconductor diodes, two 50 MFD capacitors, and a resistor will do the job quite nicely. The voltage will be reduced for the 12AX7's plates accordingly.

Now for the hunker. The 4-250a wants about 3,000 to 4,000 volts on the plate! My other microwave oven transformer will have no problems providing that voltage. However, high-voltage semiconductor diodes will be expensive, but obtainable. The capacitors will be a big issue too, but I'll make something work. More than likely they'll be huge and Soviet surplus, but they'll do the job just fine.

Last is a low-current supply that is capable of about 100 volts to provide bias to the 4-250a. As for biasing the other tubes, I have yet to figure out what kind of biasing I am going to use. More than likely the 12AX7 will be grid-leak bias. The other one might wind up being cathode biased. I'm going to experiment with different types to see what I like best.

That's all for now, folks!!!

Current Location: In Soviet Union, you are location!
Current Mood: geeky
Current Music: None, until I make this thing work!

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I have been working on some nixie tube clocks for quite a while. I have one completed, and another in the designing stage. Almost everyone who builds them uses PICs or microcontrollers. Well I say NAY to that! My first one uses three different kinds of logic: CMOS, TTL, and RTL. It uses a DS32KHZ to generate the main clock signal, and then it is fed to some 74HC4040 binary counters to divide the output down to 1 Hz. That signal is fed to some more 74HC4040s, which feed the input of some CD4028 binary to decimal decoders. From there the signal is fed into some MPS42A high voltage transistors which feed the cathodes of the IN-14 Nixies. The binary counters are reset and counted at the appropriate times using some RTL gates of my own design. Enjoy, yo! Note that the last hour digit is just a neon lamp, as I felt that using a nixie to display either a 1 or 0 was just a waste of a perfectly good nixie.

However, my next design for a nixie clock is even more insane. To get as far away from PICs or microcontrollers as possible, it will not use even a single integrated circuit! It is going to use solely RTL logic, again of my own design. It will feed the 60 Hz sine wave coming from the power supply transformer into a differential amplifier, which will convert it into a clean square wave. From there, it goes to a divide-by-6 counter, which takes the 60 Hz square wave and divides it down to 10 Hz using a series of gates and flip-flops composed of bipolar junction transistors. This part of the circuit is shown in the schematic that I have uploaded, and you can see how it looks on the breadboard. And this is only the first part of the circuit! From this divide-by-6 counter, the signal will to go a divide-by-10 counter, with an output of 1 Hz. Then it goes to another divide-by-10 counter to feed the first digit of the seconds nixies. Then it goes to another divide-by-6 counter, then to a divide-by-10 counter, and then a divide-by-6 counter, and then to a divide-by-12 counter to feed the hours nixies, with the last three numbers (10-12) decoded using diodes, rather than having to go to another counter and support circuitry for it. The first divide-by-10 counter is tapped at two places to feed to a divide-by-2 counter to control the colon flashers. Current estimates are around 300 transistors, 600 resistors, 150 capacitors, and about 100 switching diodes, plus hardware!

Current Location: College Station
Current Mood: crazy crazy

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Check out these awesome pictures that I found out I had from who-knows-where.

Current Mood: artistic

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Suppose that the world is far different from how we perceive it. Suppose that all we know is just a figment of our imaginations. What we see, feel, taste, smell and hear is only perceived as such because our mind tells us so. How does one really know that another exists? What if our clever minds falsify another being and makes us believe it is so? This, I submit to you, my friends, as a deep explanation of the world and how it works.

Earth shattering, I know...
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Finally, I was able to put up some images of my awesome Tannerin! Man am I great!

Current Mood: cheerful cheerful

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For about two weeks now, I have been building a musical instrument called a Tannerin. Here's a link to a website that gives a good description of what a Tannerin is.


Anyway, I have finally finished building mine. I designed it from scratch, too. I'm so happy! It has 6 selectable waveforms, a volume control, a pause button, an amplifier output, a headphones output, a flat frequency response, and it can powered by a battery. Unlike most of them, which are analogue, mine is digital. It works on the same principle as an MP3 player. Therefore, mine can't make a true sine wave, but I can program any waveform of my choice into it. Here's the schematic to the thing.

Basically, it rocks, and I love it.

Current Mood: accomplished
Current Music: Good Vibrations

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This semester is over! Man that rocks! I finished my finals today, so I am done. Tomorrow, I get to go home, which also rocks. I would go tonight, but it is just too late, and the lack of a car is proving to be quite a hassle, especially since my bike tire went flat. At least I fixed that. I'll work on my stories some more as well. I just love how well they are coming along.

On a side note, I also took up art again. Then again, whether my "art" is art truly depends on your concept of art. I am apparently quite talented in that field, however. Oh well, I best be going. My girlfriend is going to call pretty soon, and I can't wait!

Current Mood: ecstatic ecstatic

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