WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
If you are not using a phonograph you can passively integrate any amp simply by putting a potentiometer(volume control) in the signal path between the RCA plug and the driver tube. If you are going to use a phonograph you will have to build a phono section which means the kit will not be that simple. Single Ended amps have a simpler circuit than Push Pull but have much less power so your speaker choice is much more important. If you are planning on building your own speakers as well you can buy your drivers to go with your amp. You also need to tell us what your idea of inexpensive is. Another thing is do you have the proper tools?
As an addendum to what David said, smaller amps tend to have lower gain, which may not always be enough. Check the amp's sensitivity (how much voltage to drive it to full power) and compare it to your intended source.
You try and cover it all and just look! We make a pretty good tag team there Grey. I do try and keep my head above water but if will find me drowning every once in a while, just bail me out.
I thought I would use this thread instead of starting another for basically the same queston.
I have just been bitten by the full range driver syndrom, I can hear Walker, ThomasW, and Grey groaning now. Yes, it is a bit weak in the bass section, but.... You are hard pressed to find a smoother sounding speaker for those great jazz tunes. I could hardly believe my ears on the first cut where I heard a sax player climb the scale and there was no humps or dips in the response.
I found this pair of full range drivers in a disposed old console stereo! And so for kicks I slapped together an octagonal transmission line tuned for about 50Hz and dropped them in. I know this is so cliche, but I have been having a ball listening to them, about 5 hours straight. Unbelievable for vocals and jazz.
So I have decide to completely lose it, a I want to build a tube amp to drive them. I don't know the sensitivy of the speakers, but I can run everyone out of the room on about 2 watts according the power meters on my power amp. This will be my first valve amp and so I am looking for a simple, very simple, inexpensive, and sensitive amp to build. I want to drive the amp directly from a CD player and I will build a passive pre-amp or volume control into the amp. Again, fellas, this is to be a quick, cheap, and easy amp that will let me get my sea legs.
I wish I would taken the old Scott a friend offered me many years ago when I was a smart *** kid and thought that if you did not have at least 100 watts of solid state, you were still living in the past. If I only knew, he told me I would wish that I would have taken someday!!!
So, I am ready to start glowing in the dark!!!
Surf, Sun & Sound
PS. Walker, I just dropped a really good jazz vinyl on the turntable, so I must run. Hope you enjoyed tonights jazz segment on ABC. I missed it, because I was listening to too much music!!!
I picked up some new Coltrane yesterday...
Your main expense is going to be transformers, both power and output. (By and large, an integrated amp is going to be too small a project for such options as OTL.) You'll need to figure out how much you want to spend, and start cruising for schematics that look like they might do what you want.
As with all amp projects, start from the back and work your way forward. How much power are you going to want? That will narrow down the choice of output tubes--there are really only about a half-dozen in common usage. (If you decide to go single-ended, you've got a different list of tubes to choose from.) The output tube will determine the output transformer (plate load). The input and driver stages will give you plenty of leeway to express your creativity (i.e. modify the thing out of recognition).
For the preamp stage, you can throw in just about anything you like, including the kitchen sink.
Oh, yeah, just for fun, keep in mind that a pentode output tube can be operated as a triode. Better sound quality but reduced power output.
I would like to keep this an inexpensive project, because as you know the budget will always balloon to triple of what you expect. So of course I will need an amp that does not need to use any rare or hard-to-find tubes. So am I asking to much to build a simple tube amp for around $100. I know that you can spend 100x that if you want, but not yet. The speakers that I am going to use it with are not worth an expensive, tedious project. If this is a bit too optomistic, I may just put together another JLH 10 watt Class A to drive this speakers.
Johnny Coltrane?! I have yet to put him into my collection. My better half is not a jazz lover(but is a music lover), so I have to budget my music expenditures accordingly.
I dunno about the old amp. Stuff like that scares me, particularly when they say "as is." Keep in mind that you'd probably have to replace all the resistors and caps, too. The caps I wouldn't trust not to pop if they haven't been run in a while. The resistors are most likely carbon composition, which probably started at 10% tolerance, and has since drifted to 50% tolerance. (Carbon comp. resistors absorb moisture from the atmosphere, etc.--they just don't age well.) And the transformers...who knows? They might be good, they might not. Relatively speaking, that's what you'd be paying for, as the rest of the circuit is mostly obsolete parts at best.
I'm assuming that you're wanting something smallish, yes? Fine tune me a bit as to where you want to go.
Both (assuming that Christine is headed in roughly the same direction as Sx3),
Poke around on the web looking for something with, say, a push-pull 6BQ5 output stage. That will put you in the range of 10-15W output. (What the 6BQ5 might be in European designation, I'm not sure. Christine, where are you, at least in terms of continent?) I'll try to scratch up a schematic or two if I have time this evening (I'm at work).
Small is good as I have a very small living space...30 foot trailer and it moves around the country quite a bit. Wattage... not more than 5-8 ish. I need the amp/preamp all in one...so maybe you can use the same power trannies for both?? No input switch...single source...Dual pot Alps or Noble?? I can probably get some metal work done at some local sheet metal shoppe. I can get the caps and resistors from M. Percy in Nevada City, Ca. Maybe the tubes too...I would like to run the amp/preamp into a set of BS-1 from Joe. I think Herb Reichet (SP?) wrote a nice review somewhere.
I will be using a CD player as a source....DIY interconnects for sure.
Wouldn't you know...it's a busy night at work, so I'm not getting as far as I'd like on the 6BQ5 hunt. Incidentally, the 6BQ5 seems to be an EL84 in European nomenclature. www.machmat.com/schema/index.htm has numerous candidates for your viewing pleasure. www.triodeel.com/schindex.htm has some of the same schematics as machmat, but also some different.
Somewhere in there, I think I saw an integrated (as opposed to straight power amp), but I'm so flustered and distracted with things here that I forgot to take notes on that aspect of things. Given more time, I'm sure I could roust up a few dozen more, but those two sites above will keep you busy sniffing around for at least an hour or two. Be patient--both sites have amps using all sorts of power tubes, and you'll have to wade through 6550s, 6L6s, and 6CA7s to get to what you want. Machmat, at least, has a breakout as to what tubes are used in each design. Triode sometimes says, but usually not--you'll just have to peek at each schematic to see what it is. Break out the eggnog and take notes on any designs that you find particularly interesting, and we'll meet back here.
If I have time, I'll see what else I can dredge up.
P.S.: For output (and power) transformers, consider www.hammondmfg.com.
The 125D, 125E, and 1608 transformers looked like good possibilities for what you're wanting to do.
Here is a schematic of a amp using a pair of 6BQ5's in a push-pull configuration that looks fairly simple. It is from the Triode Electronics Online site. Here is the link - http://www.triodeel.com/dyna6bq5.gif
I know that this image is a bit overbearing, but I could not resize it.
I do not know enough to be able to pass any judgement on it. Anyone have a clue what wattage this amp would run?
I have found a reliable source for all the parts I need except the transformers, both power and output. All the price I have seen will break the bank, anyone have a suggestion for a source of transformers in Australia that are reasonablely priced?
At a guess, I'd say it's closer to 15W than 10, but the actual output will depend on the rail voltage, which will in turn depend on the power transformer you choose. A lower rail, say 250-275V, would give lower power. Tube circuits are not that finicky about what rail voltage you use as long as you don't exceed the ratings of the tubes.
I'm afraid I'm no help on Australian parts.
For what it's worth, if Dynaco (David Hafler prior to the Hafler company) made it, it's probably as near bulletproof as you could ask for. As a footnote, he was one of the two guys responsible for inventing Ultralinear operation (the mode of operation shown in this circuit--note the extra taps from the output transformer going to the screen grids). A very clever man.
A solid state rectifier would be cheaper and easier than the 5Y3 shown in the schematic.
A good choice for a project.
Christine, you need not choose the same circuit.
I have been doing a cram session on tubes tonight and have put together most of the theory in my head. Please do not misunderstand me, I do not consider myself suddenly a tube amp expert, far from it. But one thing that is not coming together is how to specify the output transformer. Could you enlighten me on the fundamentals of choosing an output transformer?
But the article is not clear on the output transformer or if this amp can be used alone to driver a very efficient monitor at low-levels. It appears that he is using this amp as a pre-amp of some sort. How can I put this amp to practical use?
Thank you. Grey, for taking time to be a mentor. I am just learning about how to glow in the dark!! I sometimes feel like Harry Potter, with tubes, because there seems to be such a mystique and aura surrounding valves and the people who use them!! Uh-oh, we might start writing a chapter of Sci-Fi here if I don't stop soon!!!
I've been battling software, trying to get a circuit board layout squared away for people who want to build Alephs (see that thread for the gory details--assuming that you have enough morbid curiosity). And, to make matters worse, I can't remember the spell to utter to make it all come together. Anyway, the point being that I'm tired, so this may not make sense. If not, say so, and I'll make another run at it later.
Step 1--Information. Go to www.triodeelectronics.com and find the tube data section. Download the sheets for the 6BQ5 (there are at least 4 or 5 page images).
Step 2--On page 2 (?) you'll find a couple of tables of numbers for class A, class AB, class B, etc. For this amp, it's safe to assume class AB, but we'll get back to this in a moment.
Step 3--Look for the plate load. It'll be on the order of 4-8k ohms. It will vary somewhat depending on the rail voltage, the bias, etc.
Step 4--Go to www.hammondmfg.com (or any other transformer site that makes you happy) and look for a 10 to 20W transformer that presents a plate load close to what the data sheet said.
Step 5--If you don't find one that's exact, it's okay. The tube may want 5.5k, for instance, but your best choice of transformer presents a 5k plate load. Don't worry about it. You'll suffer a slight loss of efficiency, but not enough to lose sleep over.
Step 6--Sip some eggnog and congratulate yourself on a job well done.
Sources (retail) for transformers. I don't know about Australia, but I'm sure that American retailers will be happy to ship to you. My advice would be to wait a week or two until Christmas is over so that UPS/FedEx/USPS have a chance to catch their collective breaths. Note that these will be fairly small transformers--the size of your fist or less. Shipping shouldn't be that bad. Christine, if your travels take you as far as AZ, you can save postage. Try Antique Electronics www.tubesandmore.com for transformers and tubes. (Christine, I think you'll find that their tube prices are better than Percy, although they don't carry as many high-end parts. The last I looked Percy doesn't sell transformers at all.) They're good people.
P.S.: Sorry, forgot about the 12AX7 circuit. (The "12's" i.e. 12AX7, 12AT7, and 12AU7 are all small signal tubes, and good ones at that.) That's a preamp, not a power amp. Won't drive speakers. Might be a good choice for a front end for this amp should it not have enough gain to suit you.
Grey, thank you very much for your time. It seems that there are a lot of people on this forum including myself that would be lost without your consistent and very frequent guidance. Maybe Jason should think about hiring you as a full-time consultant!!
I will do the research necessary to learn about output transformers.