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Discussion in 'Shock Brother's DIY Amps' started by linux, Oct 4, 2018.
Speaking of solder, avoid 'leadfree' solder like the plague! 60/40 Pb/Sn is the only way to go.
I would say definitely something to read value on caps, good to have the ability to check ESR too (especially when doing repairs).
The lamp filament shares the supply voltage with the amp. If the amp has a short, the whole 120V appears across the filament and the bulb lights up as it would in normal use. A 120V/200W bulb passes 1.67A at full brightness meaning that 1.67A is the maximum current that can flow in the amp.
just to play the Devil's advocate: I have no training in electronics, only a bit of self-education from old RCA tube manuals and the Jack Darr book. I have built 10 or 12 ampsw, all but one from scratch using salvaged and surplus parts sourced locally when possible. The last amp I built was a Mojo kit - what a luxury! The first amp I built, in '93 (?) was a 5f6a copy. Way over my head, but it worked.
I have never had a working oscilloscope. I picked up a few non-working ones, but I was spending more time trying to make them work than I was on building my amp.
I haven't had a wave-form generator either. Just recently I built a little gizmo for tracing signals, it includes a 1kHz tone generator. Never used it on a guitar amp yet, only on pedals and little things.
THD monitor... why, I wonder? The amp sounds the way it sounds. Anyway, I never even seen one of these in person.
Dual power supply... which two powers are you gonna supply? sounds cool, but I have never used one.
Variac - YES! I found a variac and built it into a box, and looked for ways to use it. I never did find a way to use it. I have heard about bringing up amps slowly, and forming caps, etc. But I don't have the patience for that.
2nd DMM - I got one! pretty handy, too. Mine cost about 10 bucks... so my second DMM cost almost twice as much as my first DMM. The second one only takes 250V, sadly. The first takes 600V, so it gets most of the tough jobs.
Soldering station? ha ha ha!! 60-watt Weller pistol-grip is all I ever used (until I tried building those blasted foot-switch things!)
I agree with the posts above: a light-bulb limiter, and a chopstick. And get to work!!
The light bulb limiter is a cheaper alternative to a variac... if you have a choice, bringing an amp up slowly with a variac is more effective than the light bulb method in some ways. But variacs are expensive. You don't really need both, IMO, but the limiters are easy to build, no reason not to if you want.
Thanks. I agree with you. Even though the hoarder in me wants a bench with all possible doo-dads on it, the light bulb trick is cheap, and cool
While I have an educational electronic background most of my time has been doing process equipment or building controls, industrial stuff that doesn't include board level stuff. Well a little board level but unless you are set up for doing that kind of stuff not worth the time. Only started on tube amps maybe 7-8 years ago. Just hacking amps together for fun, not really working on factory made amps. Given that I have a different take on it than someone working on amps for others.
A couple of DMM's. Reasonably cheap ones can come with a capacitance meter in it, I have even seen some $20 ones that are accurate. But get one good one that is fairly rugged and easy to work with and use it as your main meter. GOOD test leads. Silicon flexible insulation rated at least to 600V, naturally the meters also. I trust my life to my leads and my meter at work (up to 600V and tons of current available), a tube amp does not have the current to blow you across the room but there is enough poke in our supplies to make your body throw itself back. Leave one meter reading current, the other watching the voltage, I need a minimum of two.
Forget decade boxes, have one, takes up too much room on the bench. Get an assortment of resistors and capacitors. I have a variac, got it given to me. Handy if you are going off the beaten path but if you are doing standard designs you can get by with a light bulb limiter. (says the guy who never used one) Just because I thought of it, not electrical, but a unibit, or step bit. Great for drilling holes in sheet metal. Playing around I use my meters to see the dc in the circuits, you should get a feel for what you should be seeing. Ohms law and voltage drops and currents should be something you automatically think of, much more important than gear. Diving in deeper then it is time to break out the scope and signal generator. I think the two go hand in hand. You can do the computer or phone thing as the signal generator but if you are going to do this build a little amplifier, even an IC chip amp powered from a wallwart. If you blow it no big deal, blow your phone accidentally... Same goes if you are using a software scope and do not want to blow a sound card or worse. Isolate it with a sacrificial lamb of a circuit.
A load. Get a few resistors and bolt them on an aluminum plate or heatsink. I have a ceramic form with nichrome wire wrapped around it that was originally used to dump lots of watts, maybe 3-5 kw. I just move the test lead over to the ohm value I want, doesn't even get warm. You come across stuff being thrown out in industry. Test leads. The funny thing is I have no problem with the bundle you can buy online, no idea what the voltage rating is on them. But these are to hook stuff up, I don't clip onto live HV with them. I also use breadboards, yes the ones you stick part leads into. If you leave a few traces unused between high voltages they are fine, at least up to 300V. Easier to build up circuits to try. Ever think of where the term breadboard came from. Back in the day when tubes were the cutting edge technology it was not unheard of hammering a few nails in a board and tacking parts between them. Throw a sheet of galvanized sheet or aluminum flashing under the board and use an alligator clip to connect it to ground and you have a half a-ss ground plane. Not as good as a real chassis but if you are just messing around not bad.
Just some thoughts.
What do you do with the charge in the power filter caps before working in the circuit?
Many of the amps have bleeders that drain the caps.
For those amps without bleeders, the tubes will drain the caps for you, especially if you power off without standby.
The cases where an amp had no bleeders and no tubes installed, I might had to wait a few minutes.
And for a situation where we're taking about 50vdc or less and you need it at 0vdc, a test clip shorting v1a plate to chassis gets the job done too, no sparks.
The smart kids got this covered. FWIW I’m in the KISS camp, and I don’t mean Gene Simmons.
It may have been mentioned, and you likely have ‘em already, but mini-grabber DMM probes can save time, frustration, and maybe your life.
That Eico 460 is primitive by today's (even yesterday's) standard, but if all you're doing is audio work it gets the job done. Find a working example at a ham fest for $15-20.
when you accumulate 3 or more multi meters, its nice to have an analog one, for certain needs.