Newby here: Just picked up an old Sparton Radio. Should....

I be able to hear anything if only 1 of the 5 tubes is not working? Sorry for the novice question, but I am just that.

I picked this up from a guy who collects junk and thought I could use it as a project to get my hands dirty in this hobby. I am not even sure of the model because I can't find it anywhere on the net.

When I plug it in, all I get is some buzzing from the tubes and one tube does not light up. I hear nothing from the speaker, not even white noise,making me think the speaker is shot also and I should just junk the thing.

Any advice on this is greatly appreciated.

Thanks and Cheers!

One tube not working is enough to kill the sound in any monaural player.

One of the tubes supplies the high voltage for the other tubes. The rest of the tubes hand the signal from one tube to the next. If any tube is not lit, it acts as an open circuit, stopping the signal at that point.

Because the audio output tube has more work to do than the other tubes (Other than the power supply tube), it burns out more often. If the output tube fails, the speaker is essentially disconnected - it won't make ANY sound without that tube.

There is one thing that bothers me. Every Sparton set I ever saw had series-wired tubes. I never saw one with a power transformer to supply heater and plate voltages.

In a series set, if one tube burns out, all of the others should go dark. Except for another fluke, the entire set should go dark. That fluke is a heater to cathode short. The cathode is usually connected to the chassis in most tube circuits. And here is the weird part of that: One of the lighted tubes could be the troublemaker.

In a transformer set, if one tube goes out, the others remain lit.

DANGER:

Be extremely careful when working with a set with no transformer to supply power (only the speaker output transformer is there). Touching the metal chassis with the set plugged in can KILL YOU. These sets have the metal chassis (and all of the knob shafts) connected to one side of the power line, and rely on the insulating case and plastic knobs to protect the user from the power. All you need to do is touch the chassis and a grounded object (a workbench, power tool, water pipe, or furnace duct) and you are connected across the power line. Even worse, the power switch often switched the connection to the chassis, making it change polarity when the set is turned on or off.

In addition, a series dropping resistor reduces the heater current to a safe value. IT GETS HOT. Don't touch it while the set is on, or for several minutes after the set is turned off.

Remember that the plate voltages in either kind of set are well over 100 volts. And the filter capacitors can store this voltage after the power is turned off.

You can tell a series set in two ways:

- There is no large (an over-3-inch cube) transformer.
- The tubes have high voltages (the first number in the tube specification is the filament voltage). These voltages are often 50, 35, and 25 volts, with a few 12 volt tubes mixed in. A transformer set has ALL low voltages (5, 6, and 12 volt).

I can't thank you enough! Awesome info.