Tech Forum

First thing- do NOT plug it in again. You can easily do irreversible damage by putting full power to an old receiver. Do you have the make & model? There are certain procedures to be followed and I can help walk you through them. Let me know through the comments.

Since I don't know what kind of shortwave receiver we are talking about, I have some general comments. It might be useful to check around your local community for assistance as many radio/TV repair shops and radio amateurs have the tools to diagnose the problem.

Since replacing the tubes did not fix the problem, then unless you can identify something external to the unit, additional effort will likely be required to troubleshoot your radio.

The problem you describe could be caused by any number of component or connection failures. Replacement parts for those older radios, if needed, may not be readily available today - kind of like finding parts for an old car. If it's a major brand of radio, then you might have some luck finding the manufacturer's website to get more information.

There are websites that advertise tube and/or old-model radio and TV parts that may be able to help. It may also be useful to look on line to see if you can find some technical specs, such as Sam's photofact, for your radio.

Nearly any serious restorer of antique electronics, especially old radios, will first replace all electrolytic and paper dielectric capacitors in the receiver. This is especially true if the radio has been in storage for a long time. Electrolytics dry out and power supply filtering and decoupling become poor. Paper dielectric caps get leaky over time. But paper only. Don't worry about ceramic and mica caps at this point. And don't play with any caps in the "front end" of the receiver as these are rarely paper except for a few that may be in the power supply decoupling circuits. These, you replace.

A leaky coupling cap on the grid of an audio preamp in a higher-power output amp can cause that tube to go into full conduction and drive one of the output tubes full-on to the point that it will burn out the primary of the output transformer, a common problem in many old console radios.

Your best friends will be found on the forum at [url=http://www.antiqueradios.com]http://www.antiqueradios.com[/url]. These guys, if they don't own your particular model, will know about it, and will be able to help you tremendously in it's repair and restoration. Don't visit the forum as a lurker. Sign up. It's free (but they'd like a donation, if possible). And then you can be set to be notified when there's activity on your thread.

And don't throw away all those tubes you replaced. There's probably nothing wrong with them.

Since you are producing "static" you know the power supply, final amplifiers and speakers are O.K. Short of having a schematic and using a signal generator and oscilloscope to check for proper operation, I would replace all of the capacitors. Old capacitors have a tendency to go bad more so than the inductors. An old technique involved "jumpering" a known good capacitor around a suspect one, but in the case of an old unit, replacement may be the best approach.

Also check for cracked resistors, loose wiring (I am assuming this unit pre-dates circuit boards), and clean the switches, contactors and tuning capacitors. IF this fails you need a signal generator (frequencies covering RF and IF for the unit) and an oscilloscope to check the circuit for the faulty stage(s).

To fix the problem you need to find the defective part(s). You should look for a schematic that has normal voltages listed; if the voltage is very different than normal, change the associated capacitors. Also measure the resistors; they are color coded, you can look that up, if the value is more than 20% off, the resistor should be replaced. Some restorers recommend replacing all the fixed capacitors because a leaky one can cause noise but not affect the DC voltage.

A Google search for "vintage radio schematics" will turn up many sources, some free, some not. Riders schematics and Sam's photoFact are also sources.

I assume your radio is wired point to point (not a PC board); in those radios the wires were pushed thru a hole and wrapped around, making removal difficult. I recommend cutting the wire of the old part long enough that you can make a loop in it, and then loop the wire of the replacement part through the loop and solder.

Welcome to the world of tube radios! Understanding basic tube radio circuits is not difficult. There are many antique radio web sites, and a good book on antique radio repair is an excellent investment. The schematic for your radio is probably available on the Web, and along with a good web site or book it will help you troubleshoot your radio efficiently.

Finally, remember that vacuum tube circuits contain lethal voltages, including capacitors that can hold a charge even when the radio has been unplugged. Good web sites and books about antique radio repair include information about working safely with high voltages. Have fun, and I predict you'll end up with a whole new hobby!

The first thing a novice tends to do when confronted with a malfunctioning piece of vintage gear is replace all the tubes.

Unfortunately the tubes are almost never the problem, in fact out of a dozen or so tube radios and similar gear I've worked on, I think I've replaced a grand total of three tubes between them all.

The first step is to locate a schematic for the set, you didn't mention the model so I can't help you there. Next, look online for antique radio restoration resources, there are a lot of them out there. One thing most experienced restorers will tell you is replace any electrolytic capacitors before you even power it up. The next most likely suspects are the tubular wax paper capacitors, check them all for shorts to begin with, then replace them a few at a time. Next, it's common for the resistors in those old sets to drift in value, you will probably find more than one that are far out of tolerance.

Resist the urge to replace tubes unless you have good reason to believe a particular tube is bad. Also never, under any circumstances, start randomly messing with adjustments until you know what they all do

Replace all the capacitors. Kits are available on line, do a Google search. Replace the capacitors, one at a time so you don't make wiring errors. A friend of mine used to restore these old radios, and the first thing he did on a full restore was replace ALL the capacitors.

We need more information about the receiver. What bands (frequency range) does it cover and what antenna are you using. Generally, you need a long wire type antenna that is 100' or longer mounted as high as you can get it. Propagation will affect what stations you can hear. You may be listening to a "dead" band that will come to life at another time of day.

Also, many shortwave stations have been relocated to different frequencies in the last ten years to free up spectrum for other use. It's possible your radio is listening in spectrum where stations have vacated. Finally, the restoration of a "boat anchor" is often more complex than just a re-tube and clean up can fix. A common failure is with old electrolytic and paper capacitors.