Topic: Restoration of a 1934 RCA radio.

[mowinmachine]

I'm not a wizard at this stuff, but to my understanding radio waves have either "short" or "Long" wavelengths. AM ( Amplitude Modulation ) and shortwave have shorter wavelengths and these carry much further than FM ( Frequency Modulation) which uses a longer wavelength but also can carry a higher quality signal. The FCC also has regulations about how far radio waves can travel per station. In the old days it wasn't uncommon to pickup stations across the country. Nashville had a very strong signal for the Opry that could be heard across most of the country. Even when these rules were passed a lot of the "Quack Doctors" that sold snakeoil headed for Mexico and setup huge powerful stations that could overpower others in the US.

 I occasionally pickup Cuban stations and those are interesting. One is in English and talks about what its like there. One show was about getting PC and auto parts. Sometimes you can pickup ships at sea. A lot of old radios have police bands too so you could listen in to what the cops were doing. Can't really do that now.

[matts mowing]

we might restore em when we get bored. good point

[mowinmachine]

Well, the radio is finally restored. As mentioned this was a particularly difficult set because none of the components were marked thus I had to identify what they were using a schematic that was out of date.

 These sets use several different types of capacitors. The wax, paper and foil varieties under the chassis and usually a couple of larger value capacitors housed in metal cans up top. The can capacitors on mine were rated at 4uF and 8uF. Usually I just buy modern equivalents and wire them under the chassis leaving the cans up top for appearances. The + end of the new capacitors connect to the leads and the - ends are soldered to the chassis.The most confusing part of the restoration was a part of the chassis called the "resistor board". I had a heck of a time figuring out what was what and where the replacement capacitors would attach. This took days of looking at the schematic and wiring diagram. There was a mention in the schematic and parts manual that there was a 3 lead multi-value capacitor on the board. Yet I could not find it. I was suspicious about a large tar-packed capacitor on the back of the board. I wasn't able to identify it's value so for the first test I left it alone.

 Due to the fact that radios like these are 75-80 years old, it makes me nervous plugging them in the house. So I put this one out on the porch to give er' a try. I've had a few put on a fireworks show for me over the years. The first test was a failure. All the radio did was make a loud buzzing sound.Hours more were spent examining the diagram and chassis. Did I do something wrong? Who knows. At this point 2 months had been spent rebuilding the chassis so I was determined to get it working. As a last resort I pulled the last remaining capacitor- the suspicious tar-packed one in the back. Lo and behold it was the 3 wire unit. This capacitor fed into one of the main amplifier tubes. Thus since it was likely bad, it would cause the loud buzzing sound. Additionally there was one remaining capacitor feeding to volume control that I replaced. The radio worked after that.And here it is.

[George Herrin]

Beautiful...

[Wheelhorseracer]

There is nothing like a tube amplifier or radio. You don't realize how hot those tube get until you grab one right after you shut it down to check it. Blister up a finger doing that.

I'm glad it worked.

How did you learn how to do all this? I would love to learn old electronics.

[mowinmachine]

I've been working on these since I was 12. But I've only recently been getting into complete electronic restoration. There's a number of rules you need to know. Once you learn them its not all that hard. You mainly deal with tubes, wiring, and capacitors. Most radios have the capacitance and voltage ratings on them. There are generally 2 different kinds of capacitors in these radios: Electrolytic and line-filter capacitors. With Electrolytics as long as the values are the same or higher than the original you are good to go. So as crazy as it sounds, if you had a 5uF electrolytic rated at 250 volts, you could stick a 12uF, 650 volt replacement. With non-electrolytics the uF rating needs to be within 20% of the original and the voltage needs to be at the same or higher.

 Tubes are different animals. Either they are good or bad and they can be bad even when they light up. I live close to 2 older electronics supply stores that have tube testers. I bring them in and test them out. If one or more is bad I order replacements. Luckily they made zillions of these tubes so I can usually find them on Ebay for $2-$3 each.
 
 Yup, they also get HOT. If I leave any of these on for an hour or so it'll heat up the room. That's why none have back covers. They need lots of air to keep cool.

[Wheelhorseracer]

Ya..  I notice some newer tube amps that use a circuit board are enclosed.. On my old 1969 Traynor tube guitar amp I try to leave it open. Some people mount a fan to blow the hot air out.

I've always wondered.. what do they do when they bias a tube amp. Mine was done when it I first got it.I just didn't know what that meant.

[matts mowing]

looks really good