http://www.antiqueradio.org/dimbulb.htm The Dim Bulb method uses light bulb(s) in series to vary voltage to your amp. Different bulb wattages to "Ramp up" like a Variac anything that hasnt been fired up in a few years. Take note of course that Filter Caps at least should be replaced on old equipment. USE AT YOUR OWN RISK. Still better than just "Plugging it in"
Heres the text
The Dim-bulb Radio Tester
The moment you bring home a "new old" radio, the first temptation is to plug it in and try it out. That's always a bad idea. For all you know, the set may have short circuits, a defective power supply, dried-out electrolytic capacitors, or (very often) failed paper tubular capacitors. Plugging it directly into the high-amp current available at your wall plug may damage the set further or even start it on fire.
Many experienced restorers will replace all of the old paper and electrolytic capacitors in a radio before attempting to start it up. If your radio is valuable or has great personal value to you, that is the recommended course. Read the illustrated article Replacing Capacitors in Old Radios for details on how to do this. If you don't want to "recap" your radio before powering it up, read on . . . .
With a device called a variac, you can start the set at a low voltage and gradually increase the current. This allows you to detect problems before anything terrible happens. It can also "re-form" dried electrolytic capacitors, although I have not found re-formed capacitors to be very reliable. New variacs are not cheap, but you can often find used ones for around $20 to $30 at swap meets and hamfests.
The poor man's version of a variac is called a dim-bulb tester. You can build one in about as much time as it took to write this page.
Before looking at the tester, here's a diagram of what happens if you plug your radio directly into the wall socket.
o<<-----------------------------+
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120v AC Radio
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o<<-----------------------------+
If there is a short circuit in the radio's power supply, the radio behaves like a length of wire and blows the circuit breaker or the fuse.
The dim-bulb tester puts a 120-volt light bulb in series with your radio. The parts that you need are some 120-volt power cord with a plug, a light-bulb socket, an outlet, plastic twist connectors, and (optionally) an on/off switch. When you put a bulb in series with the radio, instead of bringing down the house, you'll just light the bulb.
o<<---o-(bulb)-o-----o<<--------+
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120v AC outlet Radio
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o<<------------------o<<--------+
The resistance in the light bulb limits the voltage that can reach your radio. By starting with a low-wattage bulb, and gradually building up to higher wattages, you can slowly increase the power that the aging components receive.
Here's Phil's dim-bulb tester, a few leftover electrical parts mounted on a piece of scrap wood. This one includes an on/off switch.
To use the tester, start out with a 15-watt bulb. If it lights brightly, stop! You have a short-circuit in the power supply, and should not plug the radio into the wall before investigating and repairing the fault. If the 15-watt bulb doesn't light, move on to larger wattages: 40, 60, and 100 in turn. Generally speaking, if the larger wattages don't glow, it's safe to plug your radio into the wall outlet.
Passing the dim-bulb test doesn't mean your radio works perfectly, of course. There are many other faults that can't be detected by this device. But it does allow you a safe start-up.
If you want to add an on/off switch to your tester, wire it in between the wall outlet and the bulb. If you use a three-way light socket, you can install a 30-70-100 watt bulb and simply turn the switch to increase the wattage.
A dim-bulb tester can be used to diagnose some basic power supply problems. Here is a handy procedure which I found in an old radio service book. It is used to check the transformer and input filter capacitor in a transformer-type power supply. (This will not work with an "AC/DC" type power supply, which lacks a power transformer.)
1. Remove all tubes from the radio. Make a note of where each tube belongs, so you can later replace it in the correct socket.
2. Place a 25-watt or 40-watt bulb in the dim-bulb tester and plug the radio into the tester.
3. A good transformer will cause the lamp to glow dimly after a few moments. If the lamp glows brightly, you have a short circuit; the transformer should then be disconnected and checked.
4. If the transformer is OK, put in the rectifier tube, put a 100-watt bulb in the dim-bulb tester, and try again. If the rectifier tube lights up and the lamp glows brightly, you have a short-circuit in the filter capacitor of the power supply.
When you replace the tubes in the radio, be sure to put them back into the right sockets! Although this method is quick and convenient, there are other ways to check the transformer and filter capacitors, of course.
For example, you could disconnect each filter capacitor and test it with an ohmmeter or capacitor checker. Using an ohmmeter, you should measure almost infinite resistance between the positive and negative leads of a filter capacitor. If you measure zero or small resistance, the capacitor is shot and must be replaced.
Some people would use a tester like this to "re-form" electrolytic capacitors. In theory, this improves the characteristics of the capacitor's dried-out paste electrolyte, allowing it to function again. I haven't had much success with this, but if you want to try this, here is the procedure.
1. Put your lowest-wattage bulb (say, 25 watts) in the dim-bulb tester, plug the radio into the tester, and let the radio run at low power for an hour or two.
2. Substitute your next-higher wattage bulb (say, 40 watts), and repeat the process.
3. Continue substituting higher-wattage bulbs until you get to 100 or 150 watts.
At this point, the filter capacitors are probably as good as they're gonna get. If the radio plays normally at the highest-wattage setting, it is probably safe to plug directly into the wall.
Not all filter capacitors can be succesfully re-formed. If, after completing the re-forming procedure, your radio plays with a loud hum that is not affected by the volume control, then one or more of the filter capacitors is junk and must be replaced.
Some people don't believe in re-forming filter capacitors and routinely replace them rather than take a chance that they will fail. I follow the "replace 'em" rule when restoring a valuable radio or one with lots of tubes that draw lots of current. With a small, simple radio, however, you might find that the original filter capacitors work reliably for a long time.
