First Tube Project?

Hi,

Can anyone recommend a good first project to tackle with tubes?

For example for the G9 preamp it says - "First of all a warning: This is not a project that is suitable for the beginner. If you haven't worked with tubes and high voltages before, I'd recommend that you start out with something simpler than this preamp."

So I've built several synth module kits successfully and am about to embark on a GSSL (the first time I'll deal with mains AC directly).

Assuming the GSSL goes well, is that enough practice? Are there simpler tube projects to try first?

Thanks

Steve

If you want to buy a kit, Hamptone is good.

tube warning is there because there is potential to cause serious injury or possible death. It only takes a few milivolts to stop a human heart.  That being said when my dad was a kid they were doing all kinds of crap with vacuum tubes as it was all that was around. Would go down to the pharmacy or other type stores and buy tubes off  the shelf. I mself have completed the high voltage circuit with my hand and gave myself an aweful bite. proceed with caution but that can be said with anything dealing with electricity. I would not be afraid just remember that is high voltage, dc, but high voltage none the less.

I stay well back when firing tube circuits up.

I suggest you go and buy half a dozen cheap DMM's with alligator clip cables. Connect them permanently (alligator clips - not probes) to the HV parts of the circuit, and anything else you want to test so then you don't have to go in with your fingers and probes. When you remove power, the still connected DMM's will tell you when all caps have discharged and it is safe to go in. Be alert at all times and don't assume that just because it is switched off that all dangerous voltages are gone. If you need to prod, use plastic chopsticks.

That said.....

NYD1b.....super easy. Hopefully be racking up 4 soon myself.

I usually regard 50V as a safe limit when working on stuff.

..and please make sure you see the DMM's counting down - do NOT trust a zero-reading unless you've seen it drop down there gradually (could be a bad voltmeter or connection).

PSU capacitors hold enough high voltage current to vaporize a screwdriver in an extremely loud violent eruption of blue flame when discharged quickly.

A high value bleeder resistor to ground will drain the stored current at a more reasonable and less violent rate. An led in series with that resistor will provide a visual.

Please be careful!

Cheers,
Jb

Really great advice everyone, thanks.

I'm confident I will have a safe approach as I have experience with other hazardous processes of the mechanical variety, welding, milling machines and lathes... but the devil is in the detail!

One other thing I wondered about the bleeder resistor idea...

A good idea is to have a resistor, like 10K/2W, on a cable with two clips that you can attach to the caps for discharging. But please. Remember. Take care.

Click to expand...

What's the best way of actually attaching those clips to the cap that needs discharging? A pair of chopsticks in each hand?  8)

And if you have an LED in series.. as long as that high value resistor is limiting the current to the LED sufficiently then the voltage created by the discharging capacitor won't blow the LED?

don't do this but I have discharged caps with a long screw driver, The sound of the arc was something fierce.

pucho812 said:

don't do this but I have discharged caps with a long screw driver, The sound of the arc was something fierce.

Click to expand...

The sound designer in me just went ooh! and then the father in me just went... naaaah.

What TimothyTitus said on good safety practice.  Bleeders or no bleeders the meter will remove guesswork from a job where you can't afford to guess wrong anyway.

My best advice would be to start with the power supply and learn the basic blocks forward and backward.  The NEETS (US Navy) modules are among the best for teaching this and are available online.  Morgan Jones' site is another good place for reading.  RCA receiving tube manual are another good resource.  Learning the power supply chain will set your mind at ease a great deal when it comes time to get hands on.

Always have your circuit properly fused before powering up.


Some power supplies will discharge faster than others after powering off.  Should the need arise to discharge more quickly you can build a simple discharging device by splicing in a suitable (say 4.7K 1 or 2W) resistor in between an old meter probe and large alligator clip.

For a discharging device you might try the old transmitter trick; attach the bleeder resistor to a wooden dowel rod using epoxy, with one end grounded via a cliplead and the other poking out to touch whatever you're discharging.  The rod should be at least a foot long.

Also, whenever working on any piece of tubed gear, keep one hand firmly in your pocket. That keeps a possible shock from transiting your heart.

Peace,
Paul