Safe power up and testing!

[halfbackstrat]

Evening all!

Was just looking through the forum for advice on first fire up and testing of a new amp. Found some great build/start up orders posted by Funk and Heisthl back at Christmas '08.

Here: https://tubeamparchive.com/viewtopic.ph ... er&start=0

When first building an amp, what processes do you go through to power up safely?
There's a great article here http://www.paulrubyamps.com/info.html

which I also found on this forum.
Does anyone here connect the PT secondaries up section by section?
If so which order do you go with? I'd imagine the ~660V tap to the rectifier would be the last one?

[Structo]

Hi,

I find the Paul Ruby guide to be a very much in depth article.

But, for most amateur builders, I think it is a bit too involved or complex.

I just use a light bulb current limiter and start with a 25w bulb and no tubes installed.

This will test the power supply for a direct short.
Depending on the size and number of power supply caps, the bulb will glow brightly for a second or two as the caps charge up.
Then the bulb should go down to a warm glow.
If it stays full brightness then there is probably something wrong and you should immediately remove power from the amp.
Then check all wiring in the power supply and the various nodes of it.

The higher the wattage light bulb used, the higher the current supplied to the amp.

Then if the amp uses a rectifier tube, I would install that and use a 60 watt bulb.

If those tests are ok I install the preamp tubes and test with a 60w bulb.

Finally install the power tubes and use a 75w bulb. (Always have a speaker connected when power tubes are installed to prevent damage to the amp)

If that all checks out, take the current limiter out of the circuit and plug the amp into the wall and see if it makes guitar noises.

Here is the info on the light bulb current limiter.

Very cheap and easy to build and it can really save you some $$$ and time in case there is something wrong with the amp.

[halfbackstrat]

Thanks Structo,

Do you use those same wattage bulbs for a 50W amp?

I assume you run the first bulb limiter test (-tubes) before you connect the secondaries of the PT?
Or do you just wire all sections of the amp and start with the bulb limiter?

[martin manning]

You can be as cautious as you like based on your confidence level. Powering up with just the primary circuit wired in is being very cautious. Just going right in with a 60W bulb is probably fine for anything.

Another way to go about it is to wire everything in and then use a very low wattage bulb, like 7W, and then measure voltages, beginning with the PT primary. If that is only 6VAC, say, then the secondary voltages will be ~1/20 of their expected values. Of course this won't work for checking the DC with a vacuum rectifier because the cathode won't reach operating temperature.

[Structo]

Whoops!

I forgot the link to the bulb limiter.

https://tubeamparchive.com/viewtopic.php?t=20341

Yes it's easy to make a silly mistake when wiring an amp.
Especially if the amp is more on the complex side. (Dumble)

That is a good reason to use the limiter because in most cases it will keep the smoke inside the amp where it belongs.

[tubey]

Thanks,

I'm going to use this to start up my first 100W build. I'm looking forward to it.

Tubey

[tictac]

Being very wimpy I like to use a light bulb limiter with a variac that has a voltmeter and ammeter.

After you bring the amp up with the bulb limiter without problems you can switch it off and bring the voltage up slow with the variac while watching the current draw.

I'm also using two DMM's to monitor B+ at various stages of the power supply

First power up without tubes installed (except the rectifier) then install tube once B+ is verified OK

After awhile you get used to the way a device without problems powers up...

TT