Need proper method of energizing long unused amplifiers?

[Guest]

Would some one please help me with a method of how to power up a tube and or solid state amplifiers that have been unused for several years?
I may need to replace all of the electrolytic capacitors, but would prefer not to replace any parts that are not nessasary due to expense.
A method of powering up that could reform the old caps would be good, or gently power the new caps if they have to be replaced.

Thanks

Norris Wilson

[erichayes]

Hi All,

Norris, the simplest way to bring up an amplifier is with a variac. I realize that this is not the least expensive way to go, but there are two good rationalizations for going this route:

1. If you're going to be restoring older amps regularly, the cost of the variac drops significantly as the number of amps increases. Besides, any semiserious DIYer should have one for running a new amp up.

2. You can always sell it after you're through with it, probably for the same price you bought it.

I'll post again on the details of bringing an amplifier up.

[Norris]

Hi Eric,

Thank you for the variac suggestion. Would you please let me know what type of variac and its usable voltage range needed for general amplifier duties? I am looking forward to this and your detailed information on how to properly power up the amplifiers in question.

Norris Wilson

[Shannon Parks]

Couple small tips regarding variacs:
- the 2 Amp variety is pretty cheap on Ebay and will suffice for most hobbyist needs. I wouldn't get one rated lower.
- Make sure it is rated for your type of mains AC (120V,60Hz in the US).
- Also look for one with a three prong AC input.

I picked mine up on Ebay for around $25.

Shannon

[Shannon Parks]

Dang! The electrolytic reforming page at Angela is gone. Too bad.

BTW, I would use your capacitance meter on your DMM (if you have it) and just make sure the caps are in the ballpark. You can test them in circuit (unit off of course). This will let you know right off the bat if you have any dead ones.

Here's a decent Ham page:
http://www.w9wze.org/df.php?dn=Tips/Rea ... ld_Rigs.wp

Shannon

[EWBrown]

If i remember right, the Angela page suggester putting a 10-30K power resistor in series between the rectifier and the cap(s), which would limit the current. Combining this with a variac would be ideal.

I have used an alternate method, first remove all tubes, then place a lamp socket in series with the primary, and start out with a low wattage (7-10 watts) bulb, then once the cap reaches its maximum voltage, which will not yet be full voltage, due to transformer losses, then put in progressively higher wattage bulbs, 25, 40, 60, 100, etc and monitor the cap voltage with a DMM. I used the light bulb method to refoem the nOS cap in my unbuilt Dyna ST-35 kit.

I've used this to re-form NOS caps as well as ones that have been idle for too long a time. Now my method is a little more techie, I use a Heathkit
regulated 0-400VDC power supply and bring up the current and voltage slowly. For above 400 VDC, I use a simple home built supply and variac, that can get me up to 500VDC.

If one wants to keep the look of an old amp to be original, a good approach is to "gut" the orihinal large can electrolytics, and then place new capacitors of appropriate capacitance and voltage rating inside the empty cans. The other approach is to simply leave the old can(s) in place, disconnect them from the circuitry and use indnvidual caps under the chassis.

[erichayes]

Hi All,

I was going to save this for the treatise, but Ed opened the door.

When I was a starving college student in the late '60s, I bought, repaired and sold 1930s vintage radios to augment my parental stipend. Since the cost of a variac was hysterically prohibitive, I came up with the "Saint Nick Variac".

Take two or three 15 light strings of the old indoor-outdoor christmas lights--the ones that use the large flame shaped bulbs with the intermediate sockets. I beleive these things are still being manufactured, but if you don't want to wait until Labor Day for the Christmas season to start, you might check thrift stores or yard sales.

Now, getcha a standard single gang electrical box, an ordinary duplex receptacle with screw connections and a plate of your choosing, if desired, as well as a line cord harvested off of some dead soldier clock radio or hair dryer or whatever.

If you look at the receptacle closely, you'll see that there are tabs between the screws on each side that can be broken, thus separating the two outlets. This is so you can make, say, the upper outlet switched and the lower always hot, or for split circuits in a kitchen.

Thread the line cord into the box, break either of the tabs (but not both) and connect the line cord to the two screws that are now disconnected from one another.

Plug the strings of lights together (daisy chain, outlet strip, etc), and plug them temporarily into a wall outlet. Loosen each bulb until it goes out. Then plug the mess into one of the St. Nick outlets, and the amp or radio under test into the other.

Plug the St. Nick into a live outlet, turn the power switch of the apparatus on, and screw in one bulb. Then, methodically screw in one bulb at a time in accordance with the guides I PROMISE I'll submit worthwith.

With two strings of 15 lamps, this will give a ballast of around 200 watts total, which should be plenty for bringing up most reasonably sized amps and radios.