I think you may have some company in that category.
The guitar amp I'm still working on was started in late 2014, I think. With time and energy both in limited supply, I knew it would take a while, but the plan was to try and make it usable even while still half-finished.
So I built the power amp first, then hooked up the output to an ancient and tired $5 thrift-store speaker, and the input to a Danelectro EQ pedal acting as preamp. Presto, I could already play guitar through my half-finished amp. It went to weekly jams with me, in that primitive state. Using the amp regularly at jams helped me to start to tune the clean tone to my liking.
The speaker and cab was a separate sub-project. It took weeks, including waiting for the speaker to arrive by mail. When done, it replaced the thrift-store speaker. The amp remained in weekly use at the jams (as well as at home now and then.)
The preamp started as a single triode gain stage; when that was done, it replaced the Danelectro Fish-n-Chips EQ pedal. (But continued to evolve, until it's current state, with two independent channels, and multiple gain stages.)
Now, the preamp is mostly done, and the current sub-project is designing and building an FX loop. The amp is still usable, and still used regularly. When the FX loop circuitry is done, it will be spliced in, and if all goes well, the amp will never really miss a beat.
Half-finished, but also always usable: that's what kept this project alive this long!
That should be in the dictionary under the definition of "irresistible temptation".
-Gnobuddy
A gentleman by the name of Darryl Hoy on the Aussie Guitar Gearheads forum does the most beautiful point-to-point builds I've ever seen. It's enough to make anyone with a touch of OCD weep with joy.
-Gnobuddy
Typical pentode curves - anode current doesn't change much with anode voltage, once you get beyond the "knee" at the top left corner. In this case, from the datasheet, anything above 150V on the anode causes very little change to the anode current.
No kidding about the current - the datasheet shows 300 mA anode current at 0V grid bias on G1, with screen grids at 170V!
Of course, 300 mA at 280 volts translates to 84 watts of plate dissipation in a tube rated for 12 watts.
I don't understand the reason for those characteristics in a pentode designed for audio, but the 6CW5 data looks like sweep-tube datasheets I've seen, which also have enormous anode currents at the suggested screen voltages.
Perhaps George will come along and explain why the 6CW5 has those characteristics.
By the way, did you notice the unusually low distortion in push-pull, according to the datasheet? Only 1 percent THD, though the corresponding power output isn't specified.
The datasheet also says 10% THD single-ended. To drop to 1% in push pull, much of the distortion must be even order, since that cancels out in push-pull. Betcha that means lots of juicy 2nd harmonic when used single ended - this might be an interesting valve to use in a little, low-power, SE (guitar) amp.
The suggested 3k anode-to-anode load corresponds to only 750 ohms per side (when operating in class B). With 280 volts B+, and only 750 ohms load, no wonder the current can go so high.
I have a hunch that (being specified for Hi-Fi) the datasheet amp was never supposed to be driven all the way into clipping. Probably that 750 ohm anode load was chosen for lowest distortion, and not to keep the output valves alive during heavy overdrive. It seems scarily low, for a 12-watt valve.
But I know nothing about tormenting little glass bottles far beyond datasheet limits...once again, maybe George will come along and tell us more.
If those little valves don't explode, you've stumbled onto a little secret gold-mine!
-Gnobuddy
There's no secret as to why: makes Class A viable. You can't do Class A with sweeps or RF pents, the former because the most linear part of the characteristic is well within red plate territory (unless you drop the V2K very low, and then you lose almost all your power output) and the latter because these were intended for Class C and so won't pull very much plate current at VGK= 0 (e.g. 1624, 814). These types have to operate Class AB for any significant power. PP, Class A 1624s put out -- maybe -- 10W in Class A, and that's with 600V on the plate and 300V on the screens.
You see the same characteristics for other audio finals like the 50C5 and the 6AQ5: high plate currents at VGK= 0. (For the 6AQ5 they made a concession in extending the plate characteristics since so many appeared as Class C drivers, low power finals, and frequency multipliers.)
The tube characteristics do resemble those of a sweep tube, and I like this tube for those reasons, but thats where the sililarities end.
The 6CW5 was developed in Europe specifically for a unique output circuit design known as SEPP (Single Ended Push Pull). It employs two tubes in series operating from a rectified 240 volt line. The 6CW5 is known as the EL86, but the odd filament versions have unique numbers on both sides of the pond. The 15CW5 is the PL84, and the UL84 is the 45B5. There is also a 6 volt version with a plate cap, the EL804.
The 45 volt flavor was employed in several European stereos with a special design speaker having a 600 ohm voice coil. This requires a sensitive screen grid that will see about 120 volts in normal operation, with an idle B+ around 150 volts per tube.
The schematic is found in the original 1960 Mullard data sheet, but I believe the tube design and circuit is German from the 50's, Telefunken maybe.
The 6CW5 was developed in Europe specifically for a unique output circuit design known as SEPP (Single Ended Push Pull). It employs two tubes in series operating from a rectified 240 volt line. The 6CW5 is known as the EL86, but the odd filament versions have unique numbers on both sides of the pond. The 15CW5 is the PL84, and the UL84 is the 45B5. There is also a 6 volt version with a plate cap, the EL804.
The 45 volt flavor was employed in several European stereos with a special design speaker having a 600 ohm voice coil. This requires a sensitive screen grid that will see about 120 volts in normal operation, with an idle B+ around 150 volts per tube.
The schematic is found in the original 1960 Mullard data sheet, but I believe the tube design and circuit is German from the 50's, Telefunken maybe.
Last edited:
Ah. Now it all makes sense! I remember now, I'd read about those transformer-less (valve) output stages some years ago, but had forgotten all about them.
All that was missing was some anti-matter valves, with positrons being thermionically emitted from a heated anode, and collected by a cold cathode, and they'd have had transformerless, fully complimentary, output stages.
Thanks, George and Miles!
-Gnobuddy
It started out as a proposed competition, in 2011.
(I wasn't here then; I'm a latecomer!)
Then there were some zigs and zags, ending with a few people being awarded with goody-bags by the thread founder, for their energetic participation.
And then the thread became a sort of stream-of-consciousness discussion of all sorts of oddball budget guitar amp related ideas.
I was a bit concerned this thread had finally died for good, but now you've revived it.
I actually have new stuff I'm working on that might show up here eventually, but work is keeping me very, very busy right now, and free time is almost non-existent.
If you're looking for a competition and a winner, I don't think you'll enjoy the thread. But if you're looking for a lot of ideas and creative input from a lot of different people, then you might find it quite an enjoyable read.
-Gnobuddy
I don't think that the thread will ever die, but there has been and probably will be more dormant periods.
I for one will be building more guitar amps, and due to the insanity of our current health care laws, will be operating with zero budget for 2017.
I started building my dream lab in a big basement about 2 years ago, then the money ran out. I am currently in the process of rearranging things and doing some rebuilding to suit the new reality.
I for one will be building more guitar amps, and due to the insanity of our current health care laws, will be operating with zero budget for 2017.
I started building my dream lab in a big basement about 2 years ago, then the money ran out. I am currently in the process of rearranging things and doing some rebuilding to suit the new reality.
I am truly sorry to hear what you, and tens of millions of others, are going through in the new reality. It's a crying shame.
I can't say more without bumping up against forum rules.
I look forward to more guitar amp ideas from you.
My own guitar amp project is on hold, while I am in the process of building a simple audio signal generator to test it with. Something to give me objective data on -3 dB corner frequencies, and something to overdrive valves with while I hunt for the right bias points to bring out the best sound.
-Gnobuddy
I can't say more without bumping up against forum rules.
I look forward to more guitar amp ideas from you.
My own guitar amp project is on hold, while I am in the process of building a simple audio signal generator to test it with. Something to give me objective data on -3 dB corner frequencies, and something to overdrive valves with while I hunt for the right bias points to bring out the best sound.
-Gnobuddy
I think "tehmessiah" (which was probably a typo for "themessiah", major bummer to have a typo in your chosen username) has left the building already.
These days money is tighter for most of us, and insecure employment is the new normal ( https://www.theguardian.com/busines...workers-have-insecure-jobs-ilo-report-reveals ), so most of us have to spend cautiously if we spend at all.
But, as djgibson51 says, tight budgets tend to encourage creativity, so there is still fun to be had.
-Gnobuddy
These days money is tighter for most of us, and insecure employment is the new normal ( https://www.theguardian.com/busines...workers-have-insecure-jobs-ilo-report-reveals ), so most of us have to spend cautiously if we spend at all.
But, as djgibson51 says, tight budgets tend to encourage creativity, so there is still fun to be had.
-Gnobuddy
In another thread he asked about a low powered guitar amp and several people recommended the Firefly. It is a good choice for someone who just wants to build an amp or wants one quickly. This thread is for someone who wants to learn the hows and whys of making something from almost nothing.
Let's just say that I hope the new "idiot in charge" is better than the last idiot.
This year my health care premium equals my pension check, about $2500 per MONTH. I will get a subsidy of about 1/3 of that if I DONT get a job, and I get to pay back all that money if I do. Crazy.....you know it.
I'm trying to support my wife, my daughter, her husband and 4 kids on what's left over. Tubelab can't make any money in 2017, but can't afford to lose any either.....there's a fine line it must walk, or I will have to close it down.
I'm still working on the synth project. All the parts are already paid for. It is mostly operational but kluged together on a table top for now. The benches are stripped down so that they can be moved. Trying to get some insulation in this basement to help with the $400+ per month heating costs, and that's with minimal heat in the basement. It hit 47 degrees F down here last year.
In my spare moments I have been cracking open boxes that have been sealed since I lived in Florida. I have found the remains of some failed amp projects that I had forgotten about, and enough parts to make several new ones. I found the remains (transformers missing) of what looks like a micro Champ 5C1 on perf board. I don't even remember building it, but that's where I started back in the mid 1960's. Back then I used TV and radio tubes from the local trash. This one's got a 6AU6 and a 6AQ5 with a silicon rectifier. I have several hundred of each tube, and I got them all in the early 90's, so that's probably when I built it. It would have been an obvious choice for this contest if I had only found it sooner.
I found most of the long stalled digital guitar project, and boxes full of electronics for it....can't find the neck though.
My workbench has been idle for over two months. Last week I dragged a 70 pound HP RF signal generator up on the bench so I can fix it up to sell it. Need $$$ to fund some more projects.
The sig gen is now live, so I fired up my sleeping virtual analog synth project. It's still where it was 2 months ago, except that the software that I wrote back then looks foreign to me now.....did I really write this????
While not a guitar amp, and it cost a bit over $100 to make (those pesky knobs again) it's worth mentioning here. As it progresses I will start a new thread.
There was some question about an LFO modulating a "waveform object" in several posts in the Teensy forums (dedicated to the Teensy processor boards). I have stated how I accomplished this, while others still insist that it will not work. I made a short video with an old Panasonic still camera, so the audio quality isn't great, but it makes my point.
https://www.youtube.com/watch?v=gWf8Ohfw9EU&feature=youtu.be
The sig gen is now live, so I fired up my sleeping virtual analog synth project. It's still where it was 2 months ago, except that the software that I wrote back then looks foreign to me now.....did I really write this????
While not a guitar amp, and it cost a bit over $100 to make (those pesky knobs again) it's worth mentioning here. As it progresses I will start a new thread.
There was some question about an LFO modulating a "waveform object" in several posts in the Teensy forums (dedicated to the Teensy processor boards). I have stated how I accomplished this, while others still insist that it will not work. I made a short video with an old Panasonic still camera, so the audio quality isn't great, but it makes my point.
https://www.youtube.com/watch?v=gWf8Ohfw9EU&feature=youtu.be
Same here, work and other stressful stuff. No fun for a while.
The $$ situation recently tightened up drastically at my end as well. Personal finances like a snakes-n-ladders game, all too common these days.
What is it about software? This exact thing has happened to me many times. There I am, staring at a long list of functions, with no memory of how they're supposed to interact.
I too have been wondering about things that aren't quite guitar amps, but may fit here anyway.
For example, how about budget-priced DIY guitar amp test and measurement equipment? I have an initial prototype of an audio function generator I designed to do guitar amp testing with. If anyone's interested, I can share details.
There are also plenty of guitar-amp related ideas still churning around in my brain. This time, some are a little further removed from the kind of thing RCA recommended and Leonidas copied. If there is any life left in this thread, it would be fun to discuss some of these.
-Gnobuddy
There is always life for this thread, it just requires a few people with life in their workbenches.
I have been selling audio amp PC boards for 12 years. It is normal for the business to go dormant during the summer months. Others in the DIY audio business, and vacuum tube sales report similar results. Things usually pick up as the weather cools with December usually being the strongest month. Two years ago I was selling 5 to 10 boards per week in December. This year, 3 boards for all of December.
I think it is like a foreign language. If you don't use it often it gets pushed back into a dark corner of your brain and eventually gets covered up with other dead thoughts. I got a college degree in computer engineering in 1993. During that time I wrote a complete radio transceiver test system in Borland C and used it at work to test a few thousand boards. I can't find the old code, but I'm sure I wouldn't understand it. Back then The world ran on DOS with Windows 3.1 on top of it, and a 386 was a powerful computer. Arduino wasn't even a dream yet, and C++ was something new that I avoided. That's where I'm having the most trouble right now. I still avoid any thing M$ especially C#. Windows 10 for IOT, no way.
I still have several tube audio projects left to work on and the parts to build them, so something will get built, or blown up, maybe both. I will put something in this thread in the coming months, even if I have to rip Amp 1.5 apart again to make amp 1.6. I have now rattled 3 tubes to microphonic death in my high gain pentode front end.
I used to be able to write software in "basic" on the commodore 64 and bbc micro, then I bought a dual processor 386 24meg of ram 500meg hard drive (ex server, real hot rod),moved on to gwbasic and then C. the other day I bought an arduino the control my mash-tun and thank god sumone else had allrdy written the code, because I found i don't rember how. and jeeez its only been 30 years.
You have a knack for accurately pin-pointing the source of the trouble.
There hasn't been much life in me, or in my workbench, for some months now.
I'm sorry to hear it. And if you had been selling pig-pink plastic phone cases with an apple-shaped outline on them, you would probably have sold a few thousand. That's even sadder.
I've been all-Linux in my personal life since 2001, fifteen years now. Currently using Xubuntu.
I do run up against limitations now and then, but the same is true with the Windows laptop I had to use at work. At least Xubuntu doesn't constantly spy on me, install updates I don't want while I'm in the middle of doing something important, and prevent me from doing things I want to do with my computer for no good reason.
I look forward to the fun, failures, successes, catastrophes, and near-death escapes!
-Gnobuddy