How to use a current limiter

[bnwitt]

There has been some discussion in recent threads on using a current limiter for amplifier testing so I though I would post Gerald Weber's method:

Gerald Weber’s instructions for using a light bulb current limiter in an amp blowing fuses:


Step 1. Plug the amp into the light-bulb limiter's outlet. Turn the amp's "Power" switch on and leave the "Standby" switch in Standby mode (if available).  Observe the intensity of the light bulb’s glow.  If the amp is ok, it will probably come on brightly at first as the in rush current flows and then dim down considerably.  If it does not dim, the amp has a short and it is probably the rectifier or the power transformer unless there are filter caps up stream of the standby switch and then it may be a shorted filter cap.

Step 2. If the lamp is dim (no short) in standby mode, switch from "Standby" to "On/Play". If the lamp lights brightly and stays bright, this indicates a short somewhere in the amp downstream from the standby switch.

Step 3. Remove power tubes, one at a time. If the light stays bright after a particular tube is removed, that tube can be replaced in the amp as it is not defective. If the light dims dramatically when a particular tube is pulled, the tube you just removed is shorted. If none of the tubes appears to be shorted, go to the next step.

Step 4. Remove all power tubes together. If the light dims, the problem is probably in the bias supply. If the light remains bright, the problem is (probably) a bad rectifier, shorted power transformer, or shorted filter cap - see next step.

Step 5. Now switch the amp back to "Standby" mode. If the light dims dramatically or goes out, the problem is in the filter caps downstream from the standby switch. If the light keeps shining bright, the problem is in the transformer, rectifier or any filter caps upstream from the standby switch - see next step.

Step 6. Remove the vacuum tube rectifier, or disconnect the diodes if it's a hard-wired solid-state rectifier (with the amp unplugged from the power source and drained of all power of course). If the light dims when the amp is turned on without a rectifier, the rectifier is bad. If the light stays bright without a rectifier in place, the problem is probably in the power transformer.

[Tone Junkie]

Good info, I hadn,t seen the whole write up before.
Wish i would have made one when I first got here several years ago . I learned the hard way. 
 LOl
 Bill

[kagliostro]

 

Very Good mind reminder

Thanks for Sharing

--

BTW, someone can post here a list of W of the lamp to be used in relationship with the power of the amp under test ?

(for 120V and also 220V line, so we will be happy on both the sides of the pond  )

Franco

[SoundmasterG]

I usually use a 100 watt incandescent bulb for most amps myself, but I've stocked up on 60W and 40W bulbs too. As far as the proper one to use for which wattage of amp, I haven't given it much thought as the 100W works well for most things that I have tried. It wouldn't work for the SVT that I used to have though because the variac itself in my current limiter circuit is only 5 amps. I could sub in a 10 amp variac too, but I never have needed it.


Greg