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I have constructed and built several SET power amps from scratch with old triodes through the years. They sound fine. My ears have been the measuring instruments in addition to a FLUKE Multimeter and two good tube testers, But I would like to see how square waves are handled. I think I will need a signal generator and a scope. But what?. Good quality, and easy to use are important. Can somebody suggest the equipment I will need?
You can make a decent audio test set with a good computer sound card and a plethora of free software.
Of course to do this right, good measurement quality sound cards are expensive like in the $1000 range. But you can do OK with basic quality stuff and you can always upgrade later.
Also a PC based system can quite easily do FFT and other advanced math functions where as dedicated equipment for that is very expensive even used.
The biggest problem with PC based gear is the noise inside a typical PC. A better solution is a sound capture / generator device that plugs in via USB. That way the analog circuitry is better isolated from the internal RFI of the PC.
Any DIY'er should have test equipment. A good used analog scope can be had pretty cheaply these days. My previous workhorse is a Tektronics 2215A, a 60MHz dual trace I picked up for $125 through an add in the local paper. For analog work you really dont need a lot of bandwidth, so any dual trace with 20MHz or more is fine. You should be able to get one really cheap. If you want to go modern, and get a DSO, they can be had for as little as $300 or so. Go with Rigol, Siglent or Owon for a low cost solution. For a signal generator, again used is fine, or new ones can be had for $100 or so. You can get a brand new B&K Precision 4001A from Allied for $200. Look around and find ones that fit you budget. Once you get used to having it, you will wonder how you ever managed without it.
Tenma makes a nice and very low cost (model 72-505, about $40) signal generator that produces sine wave and square wave outputs. The sine wave is very low distortion ( < 0.05% in the range 200 Hz - 15 kHz), which is handy if you ever want to make distortion measurements on an amplifier.
You will need a function generator that does square and sine waves, and a scope with a probe, or two, if its dual trace. A used Tektronix solid state scope is what I'd opt for. Maybe there is on-line apps to do the function generation.
Why don't you take the amp to a nearby audio repair facility, or a nearby university, with an EE department, and have THEM look over and measure your amp? A professor would like to do that. For as little as you will use the test equipment, it is not really necessary to buy .
What you are suggesting was probably possible 50 years ago, but not today. Digital, bits, bytes, pixels etc. rules today. We are a small extincting group.
When developing a tube amp I need the measuring equipment at hand any time to have control with the circuit alterations I do.
To rely on ones ears is ok to evaluate the end result, but during the construction process it is very helpful, almost necessary; to see what happen to the signal when alterations are done. Is a two trace scope which can compare the input signal with the output signal what I should look for? What are others using? Kits and tested schematics? Sometimes I feel I should have done the same, but I like the challenges.
I use a Hitachi dual trace 60MHZ scope ($40) + Kenwood AG203 sine/square wave generator ($60), both acquired through eBay. Just make sure you research the feedback history of sellers.
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