Need recommendations for breadboard/test setup..

Discussion in 'General Electronics Chat' started by mikedavid00, Jul 18, 2012.

  1. mikedavid00

    Thread Starter New Member

    Jul 16, 2012
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    0
    Hi!

    I would like to play around with making circuits for guitar vacuum tube amplifiers and guitar pedals. This would also involve some vacuums that would power 12" speakers etc. I would also like to possibly play with step motors down the road.

    I would be just a hobbyist, but would still like to 'save time' where I can. I read that I need a bench power supply and an oscilloscope. I'd like to setup a work table for prototyping.

    The problem is, I keep reading people saying different things. For instance, someone said to get a 15v is not enough for the bench power supply. As far as the oscilloscope, I've read just about everything. One person claimed never to buy an old one for hobby use due to features and that he guaranteed people would regret it compared to a new modern one. Then I read another say that a cheap portable would be fine for most uses. Then there's the brand. Some say the re-brandned stuff is very good, others call them toys and junk. But what is best for my use I don't know.

    So I have no clue what I need to buy in order to have a proper test setup that will fit my needs.

    Any help would be appreciated.. it would be nice to have both for $300 or less. I'd likely need to order from ebay.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Unless you are accustomed to getting what you want and your daddy has lots of dough most people would start off with what they can afford.

    A tube amplifier would need a lot more than a 15V bench supply. How about 300V?

    I would start off with a DVM ($10), a protoboard (Wishboard $10), 9V batteries and clips ($5) and some ICs, transistors, resistors, capacitors, LEDs, wire ($25).

    Total budget $50.
     
  3. #12

    Expert

    Nov 30, 2010
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    It can be argued that a musicians best wave form analyser is his ears, but that won't tell you when you have made an assembly mistake. A guitar is a fairly good tone generator but stroking your guitar while moving the voltmeter probes is difficult.

    One thing glaringly missing from the first answer is the output device. With no 'scope and no speaker, how are you going to know anything about the results?

    My opinion includes an oscilloscope, a function generator, and an amplifier with speakers. If you're going to play with vacuum tubes, you will need a filament supply in addition to the plate supply. If you're going to do audio with transistors and integrated chips, a dual polarity supply (+/- 15VDC) simplifies things.
     
  4. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Your first statement " play around " -- then vacuum tubes......tends to makes one cringe....

    12 is right...you will need a stable power supply of at least 300 AC volts, preferably a variac setup that will allow flexibility........ you will also need the regulated / filtered DC to work with the chip-audio circuits.....
    Then there is the balance of the test equip 12 mentioned...

    I also suggest some serious reading in the AAC, and other textbooks on your desired subjects...
    Start with Electrical safety..........
     
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  5. MrChips

    Moderator

    Oct 2, 2009
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    If you are planning on building yourself a tube amp this is perfectly doable, but you don't "play around" with this. The high voltages can be lethal.

    You select a circuit that someone has already designed. You acquire the components and you start building. This is not something that one can breadboard easily. You will need a sturdy metal chassis.

    From the start you will have to build the power supply on to the chassis and this entails mounting a large power transformer to provide the HV DC and the filament voltage.

    Hence for starters, you better learn how to build and connect to AC mains services safely and properly. Then you have to worry about mounting the sockets for the tubes.

    You will also need another large audio transformer to convert from the tube output to the 8Ω loudspeaker.

    In a nutshell, physical construction technique is paramount.

    Are you prepared for all of this?
     
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  6. #12

    Expert

    Nov 30, 2010
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    Apologies for the light-hearted (or is that half baked?) reply. I was thinking about a vacuum tube stomp box that uses a 12AX7 and a digital gate to oscillate the battery voltage up to 50 volts at less than a milliamp. A power supply that will drive a 12 inch speaker through a vacuum tube will definitely knock you on the floor, and might kill you. Practice working with only one hand.

    My method to get the high voltages is a Variac into a microwave oven transformer, but then, I've been doing this for 40 years. I'm not likely to turn it up until the 450 volt capacitors explode. Whatever you do, use fuses! They will keep the shrapnel to a minumum.

    Once again: dry shoes, insulated tools, one hand in your rear pocket, do not lean against the work bench, do not let people talk to you or touch you, but keep one nearby in case you need someone to re-start your heart. A fuse in every power supply circuit and a bleeder resistor on every filter capacitor.

    MrChips brings other good points in post #5. Vacuum tube designs use big transformers and metal shielding is imperative. As I told a friend, when you start building guitar amps, you suddenly become a sheet metal worker, whether you like it or not. Tin snips, a jig saw, a large bench vise (like 6 inches), hammer, center punch, a piece of black iron angle iron you can use as a straight edge for bending sheet metal, drills, a nibbling tool, nuts and bolts, maybe rivets, standoffs for the circuit boards, power cords, fuse holders, indicator lights, toggle switches...

    amazing, isn't it?!
     
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  7. MrChips

    Moderator

    Oct 2, 2009
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    Actually, I had in mind to build the exact same thing this summer to show others how it is done. But just another project to kill time.
     
  8. vk6zgo

    Active Member

    Jul 21, 2012
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    I think I know you from another place.
    Have you ever gone by the name of "Crush"?
     
  9. ramancini8

    Member

    Jul 18, 2012
    442
    118
    Buy an old (1950s) car radio and fix it up. You can buy one that works on 6 volts or one that works on 12 volts. These radios have internal choppers that generate the high voltage, they have tubes, they have an output transformer---everything you need to get a start. A guitar amp pnly needs the volume control to output stage so pull the front end tubes. Once you progress past the radio's capability you can worry about getting fancy. REMEMBER---CAR RADIOS HAVE 300+ VOLTS WHICH CAN KILL YOU.
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    For audio just any kind of oscilloscope will do.
     
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