Back when I was 18 and going off to school, I decided I would need a little stereo for my dorm room. I built a little stereo amp (and speakers) with just two tubes. They were twin tubes with one half as a preamp driving the other as a power amp. I'm trying to remember what tubes I used for that. I remember that it worked surprisingly well. I think they were small 7-pin jobs, but I'm not certain. The B+ may have been derived from the 120VAC without xfmr. I do know that cost and simplicity were important.
Anybody know what they may have been? I'm thinking that they may have been specifically designed for that purpose in mind. But they may have just been like a 12AX7 or something, then it could have been anything. Do people still do this? Most designs I see now use at least 3 tubes.
I'll expand this question to include any known ultra-simple transformerless designs.
Thanks
Anybody know what they may have been? I'm thinking that they may have been specifically designed for that purpose in mind. But they may have just been like a 12AX7 or something, then it could have been anything. Do people still do this? Most designs I see now use at least 3 tubes.
I'll expand this question to include any known ultra-simple transformerless designs.
Thanks
Sure. I'm building a 6BM8 amp that I'm gonna finish any day now, I swear...
http://i69.photobucket.com/albums/i43/Ty_Bower/DirtCheapSE/P1140836.jpg
Yeah, yeah, I've heard that before (usually from me to my wife)...Sure. I'm building a 6BM8 amp that I'm gonna finish any day now, I swear...
http://i69.photobucket.com/albums/i43/Ty_Bower/DirtCheapSE/P1140836.jpg
Thanks guys. I'll take a close look at your projects. I imagine there are some spud threads here. I'd be interested to see any such projects. I've heard the term "spud" but didn't know that's what I did (ahem) years ago. Big question is, how do they compare sound-wise to other, more conventional SET designs? I know they'd be flea power but I will have some 94 dB full-rangers to try it on. Maybe I could even find something more sensitive. I like simple. Simple is good.
Boy, that 6GW8 sure sounds familiar, but I'm not sure.
Yeah, that's the kind of thing I had in mind.
Oh, I just found the ECL82. It's a 6BM8. Sounds like a really nice project tube.
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I just picked up a ECL82 amp the other day and am about to start restoring it....
see: ECL82 mullard 4-7
see: ECL82 mullard 4-7
Not only available, but about $1.50 on the bay. I'll bet you could have a pretty decent little stereo amp for about $50-$75 with careful shopping. A couple of home made 4" full range speakers and the whole thing could be $150 and probably sound pretty darned good. We should have a contest for cheapest stereo tube amp using all new parts to keep it even and at least 2 wpc.
I'd still like to know what a system like this sounds like. Anyone?
You still need output transformers, and it is irresponsibly dangerous to build an amp without at least an isolation transformer for the power supply. I think I came up with a total of $165 for the amp that Eli mentioned in the first reply to this thread. That's still a pretty good price for something with vacuum tubes.
Can I see a quick guesstimate breakdown of what you would do? I figured that $15 Edcor's would work fine since we're not overly concerned about bass quality on a cheap build. Absolutely right about a power xfmr, I'd have to price something there. P-to-P wiring-no pcb. . A cheap aluminum chassis. $20 of misc parts. Probably shipping costs would hurt pretty bad, and sales tax for most of us. The tubes are cheap, but shipping destroys the value unless bought locally. Okay I was too optimistic, but it would be fun to see what you could do.
I still intend to do a Tubelab SimpleSE and I can do really well on it, but only because I already have a pair of 5881's and a 12at7 and some parts and chassis. Also, I'm only making it to drive the fullrange part of a 2-way, so bass is no issue so I can use $20 Edcor OPT's.
Yours looks good and the hard part done. So finish it and tell us what it sounds like!
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Surprise! That tweaked Mullard SE design has good bass. 
"Extra" power handling capability in the O/P trafo allows the GNFB error correction signal to work without causing core saturation.
On the PSU front, a well executed Greinacher voltage doubler yields high performance at modest expense. Allied Electronics charges all of $11.41 for the Triad N-68X isolation trafo. Shipping costs can eat you alive, unless you bundle your purchases. A full set of power "iron" can be obtained from Allied for that SE 6BM8 project.
"Extra" power handling capability in the O/P trafo allows the GNFB error correction signal to work without causing core saturation.On the PSU front, a well executed Greinacher voltage doubler yields high performance at modest expense. Allied Electronics charges all of $11.41 for the Triad N-68X isolation trafo.
Shipping costs can eat you alive, unless you bundle your purchases. A full set of power "iron" can be obtained from Allied for that SE 6BM8 project.Okay, this is getting interesting. I just ordered a copy of the Mullard design book and I'll find out what that's all about.Surprise! That tweaked Mullard SE design has good bass.
On the PSU front, a well executed Greinacher voltage doubler yields high performance at modest expense. Allied Electronics charges all of $11.41 for the Triad N-68X isolation trafo.
If we ever had a cheap build contest, I think this guy 5-Buck Amp might just win...
This is a different tube but does it get simpler than this? http://homepage.mac.com/planet10/TLS...s/SE_50EH5.gif I like simple. Simple is good.
Anybody know what a ceramic pickup puts out compared to a mp3 player or something? I think it was something like 100 mv @ pretty hi Z. I'll bet the headphone output on a mp3 player or PC would drive this thing. I think they can get pretty hot with a volume control.
This tube is also inexpensive and available.
Anybody know what a ceramic pickup puts out compared to a mp3 player or something? I think it was something like 100 mv @ pretty hi Z. I'll bet the headphone output on a mp3 player or PC would drive this thing. I think they can get pretty hot with a volume control.
This tube is also inexpensive and available.
The TT that was associated with the amp that one used as a donor would drive it to full blast, Suggests output from cart similar to a CD player.
dave
Pano: 1st thing that amp got was an isolation trafo.
Attachments
It's dangerous. I actually built one like it when I was a kid. What did I know? My dad didn't think much about it either. Actually, it's amazing that anyone lives past 18. I remember one time I hooked one end of a power cord to a sheet of aluminum foil and the other to a length of pencil lead. My first arc welder!
Yeah, but no need to live dangerously now!!
BTW, there is a link in the other thread - the mullard 404 one - for a free download of the mullard book.
I have an ECL86 amp that uses 2 ECL86 in each channel in PP. It sounds pretty good, and gives about 10wpc. It wouldn't have the clarity of say, the best kt88 out there, but its nice. Thats with no mods done at all, its straight as it left the maker (audio innovations).
Another FWIW, for anyone in europe at least, this kit is fairly good value:
PCL86 kit
and this one is even cheaper: even cheaper ECL86
Fran
BTW, there is a link in the other thread - the mullard 404 one - for a free download of the mullard book.
I have an ECL86 amp that uses 2 ECL86 in each channel in PP. It sounds pretty good, and gives about 10wpc. It wouldn't have the clarity of say, the best kt88 out there, but its nice. Thats with no mods done at all, its straight as it left the maker (audio innovations).
Another FWIW, for anyone in europe at least, this kit is fairly good value:
PCL86 kit
and this one is even cheaper: even cheaper ECL86
Fran
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