#1
I have a Stark function generator that my teacher (he looks vaguely like the professor from Back to the Future) gave me because its from a now 20 or 30 years obsolete analogue based curriculum. It has two Toshiba vacuum tubes: one that is identified as "8 I" and 12BH7A and another "8 J" 6AR5. There's also 115V transformer, and another transformer that is smaller. There are many rotary switches and potentiometers, resistors, capacitors, and ancient electronics I've never seen before. It's just sitting in my closet so I want to do a project to make an amp this summer out of it. I figure as simple of an amp as possible, like the very first amps ever made in terms of complexity. Does this, to anyone with a bit of knowledge about this stuff, seem feasible and any help getting circuit diagrams that would help me get started? I don't care at all about tone, this is just to be a project to get some use out of a big hunk of ancient history and experience with electronics. Also any suggestion on which tube for pre and which for post amp. Is there a data base where I could figure out how the properties of these tubes compare to more standard amp tubes?

Any help is very appreciated. Also, if you don't think I can make an amp any other suggestions for what to do with more old electronics that would be fun and hopefully useful-ish.
#2
http://www.triodeel.com/tubedata.htm

Can't help you with much else since my experience has been limited to modding, not building amps.
My Tele Project!

Cheapy Johnson Steel String Acoustic
Les Paul Ripoff w/ SD SH2 and SH4
Modded Crate V18 2x12 w/ Weber Speakers
Squier Deluxe 5-string Active J-Bass
Acoustic B100 15" Bass Combo Amp
Gray VS Jekyll & Hyde
Vox V847A Wah
#4
Indeed I would be, but (please correct me if I'm wrong) it should be safe if its not plugged in right? Is there a way to discharge caps for additional safety?
#5
Short them out through a resistor.
My Tele Project!

Cheapy Johnson Steel String Acoustic
Les Paul Ripoff w/ SD SH2 and SH4
Modded Crate V18 2x12 w/ Weber Speakers
Squier Deluxe 5-string Active J-Bass
Acoustic B100 15" Bass Combo Amp
Gray VS Jekyll & Hyde
Vox V847A Wah
#7
I apologize you feel that way. There are plenty more in his back room, they don't appear particularly valuable. That and mine doesn't work. Tubes light up, but I can get sound out of it when I plug it into an amplifier. I'd prefer to do a fun little project with it. I could perhaps acquire one for you if you were willing to part with a piece of gear.
#8
Thanks Mike. Just connect the two ends of the capacitor to the two ends of a resistor and it will discharge?
#9
Or you can ground it through the resistor. Either one.
My Tele Project!

Cheapy Johnson Steel String Acoustic
Les Paul Ripoff w/ SD SH2 and SH4
Modded Crate V18 2x12 w/ Weber Speakers
Squier Deluxe 5-string Active J-Bass
Acoustic B100 15" Bass Combo Amp
Gray VS Jekyll & Hyde
Vox V847A Wah
#11
Well if it has a built in amplifier, you can isolate the place where it stops being a function generator and starts being a tube amp. After that, just splice your guitar in there, put a tone stack between the pre and power amp stages and voila tube amp. My advice is read up on amplifier design, I couldn't get a single thing to work before i really understood how things work. If there is no power amp, but maybe a pre amp, then you could just make it into a pre amp, perhaps run a tone stack after the pre amp and have a nice little clean tube pre amp to run into a computer or a modular power amp rack mount type thing.
#12
I can't tell if there's a preamp circuit, I don't know what one would look like. But my idea is less about me getting an amp and more about building from scratch using what I have. I guess I'll just look up early simple VOX or Fender designs and see if there's anything I can simplify further. I probs won't have any tone circuit, just pre and power volume.
#13
if you go that route look up early Champs (like the 5C1) and the 5F2-A Princeton. doesnt get much simpler than those. also have a look at the micro-champ. it's a champ simplified even further.
#14
Yeah a simple class A amp would be easy. Why don't you snap a photo of the tubes you've got in there and write down what they are? That'd probably help. Also, be mindful that old capacitors can go bad so if everything seems to be good, but it still doesn't work, check those old caps. Also, I mean if your building something completely new, just get new caps to start with.
#15
#16
12bh7 and 6ar5 are the tube names.

6AR5 datasheet:
http://tubedata.itchurch.org/sheets/049/6/6AR5.pdf

12BH7 datasheet:
http://tubedata.itchurch.org/sheets/155/1/12BH7.pdf

the 6AR5 is a power pentode. that can be your amp's power tube.

the 12BH7 is a dual triode. there's your preamp section.
#17
You're proving to be a great help. If you had selfaggrandising sig you could put that in it.
These datasheets aren't only helping for this project but understanding tubes in general. Thanks.
#18
i use this site constantly for tube datasheets. never failed me yet.
http://tubedata.itchurch.org/sheets63.html

i've had plenty of self aggrandising sigs over the years
#19
Do you know anywhere where I could find not a schematic of a specific amp, but rather a schematic that defines how an amplifier works? Or maybe a hobbyist site for making random electronic gizmos including simple audio amps? I'm looking at schematic heaven already, but id be interested in diversifying my resources if i could
#20
forgot to mention that smaller transformer is probably an output transformer. you'll definitely need that. as well as the power transformer to get the high voltage for the plates.

this is a great site.
http://www.freewebs.com/valvewizard/index.html

heres a thread but it's still a WIP.
https://www.ultimate-guitar.com/forum/showthread.php?t=1223425
#21
Oh wow. Valvewizard is a great site. I guess I should have checked that thread first, it's probably stuck. I call NOOOOOOB!!!! on myself.
I figured that the smaller transformer would be suitable for an output transformer. Is there anything I need to know to tell if the transformers will provide the correct current and potential? If they don't can I break them open and adjust the windings as I see fit (maybe not, since that would require counting the probably 1000+ windings.)
Plates? what are plates? I did parallel plates in physics, are they like those.
Thanks again for all the help
#22
The transformers are probably fine i'd imagine, after all they're powering the same tubes they used to. as for plates, those are in the tubes if they're the plates I'm thinking of. Perhaps you should do some research on how these funny tube things work. http://www.youtube.com/watch?v=UM3av6moJd4 If you're like me it's kinda fun anyhow! haha. I think this is a good video if I remember right.
#23
That's a great video, about half way through part 2 everything made a lot of sense. I never really got how transistors and tubes amplified signal, but now I understand the mechanism. I wish the guy would talk faster and without a thick accent, but I'll forgive him this time.
#24
you cant break open a transforer and "adjust" it. you'd just destroy it.

the plates are the anodes of the tube. basically analogous to the collector of a transistor. just check out wikipedia for all the info you could ever want on tubes and anything else, really.