1955 Dumont Television

This article is the start of a new project. In the 1970's when I was in the military service I was station at McConnell Air Force Base. I was on a Titan II Intercontinental Ballistic Missile I only worked eight twenty-four hour shifts and one stand by per month. On my time off I worked at a television shop called Comb's TV. This is where my electronic career began, besides being in electronics for the military. I worked for Jerry Comb's as a bench technician starting off working at the radio bench working on radios and record changers. After working there for a couple of years I moved to the black and white television bench.

I have many great memories working there and sure learned a lot. When I got out of the service I moved back to IL and went back to school to get a degree in electronics. At the same time I went to work for two local TV repair shops and was asked to teach a class at Lewis and Clark Community College on Radio and Television Technology.

So this is where this story is going. I went to work for a large computer company as a computer technician and got out of the Radio and Television business forever. Thirty-five years later I see this 50's era Television in the window of an antique shop. It sure brought back a lot of memories of a bygone era. When I was younger I had some antique TV's from the 1940's and let them go before a move to the east coast and have always regret it.

After a couple of weeks looking in the window as I drove by. I decided to go in and talk to the owner. It turned out to be a Dumont TV but did not work and the owner was afraid to plug it in. We talked about a price but I decided not to buy it (still to much money and not sure were I was going to put it). After a couple of weeks the owner came into the bicycle shop that I work at part time. He said that I could have the set for the price I quoted him.

Here is a couple of ads for Dumont:

I was pretty excited to see how the chassis looked and if I could still repair a old TV set. Looking on the Internet I found a schematic for the TV set around 15 to 20 dollars. I then looked in some of my old books and realized that I had the original schematic in my archives. That let me know that I was destine to have this TV. I started by taking the chassis out of its case and realized that the picture tube was separate from the chassis. Most of the old sets of that era had the picture tube attached to the chassis and everything came out as a single unit. I had to get the picture tube close to the chassis so that I could hookup all of the connections.

Here is a picture of my setup:

Starting the repair process included powering the TV on with a variac. I turned the variac on with no voltage applied and slowly turned the power up to about 40 volts and let it set there for about 10 minutes. This allowed the voltage to come up slow and not stress the power supply with a high current draw. I then brought the voltage up to about 120 volts and listen for any problems.

The first problem that I had, I could hear the horizontal oscillator squealing. At this point I had some sound and no high voltage for the picture tube. I decided to work on the high voltage first and see if I could get it operational. Hearing the horizontal oscillator squealing told me that the oscillator was off frequency. In that case it is always good to look at the signal coming out of the oscillator with a oscilloscope. I could see that there was additional pulses on the signal. I scoped the cathode of the tube and had pulses on it. This was the problem it connected to a electrolytic capacitor that looked to be open. I was able to take a old capacitor that I used to subsitute in the circuit and the squealing went away. I checked to see if I had high voltage at that point and I still did not. I tried to pull a arc from the plate of the horizonal output tube and that worked so I went a little farther and tried to pull an arc from the picture tube. I still had no output. I went back to the flyback transformer and was able to pull an arc from the filament winding and it worked so I knew that the flyback transformer was good so I replaced the high voltage rectifier tube 1G3. That fixed the problem and I got a picture.

Here is a picture of the picture tube working: As you can see the show playing is Gunsmoke with James Arness (Matt Dillon). How good is that?

I had substituted in a couple of electrolytic capacitors to get the TV set to work. The first thing that I need to do is replace those electrolytic capacitors. It is amazing that the old caps work as well as they do since they were 57 years old. I check a couple of sources and one was Antique Radio Supply. They had some that might work at a cost of 35 to 40 dollars. That was going to be pretty expensive and I never like to spend more that I need to. I had known in the pass that some of the antique radio technicians were rebuilding the existing can-capacitors in their vintage equipment. I used the internet to help in the rebuilding process.

On the internet a lot of the technicians were using a pipe cutter or their metal lathes to cut the can-capacitors close to the bottom of capacitor base. Then after they substituted new capacitors in the can would either epoxy them close or use tape to hold the can together. I did not like either of those methods. I did find another site where this technician had pried open the bottom of the can and then took out the metal ring. This seem to be the best approach for me. I liked this ideal because when you are done the capacitor looks original. I will write up the procedures to rebuild a capacitor on this website so stay tune.

Here is a picture of what the capacitors look like:

The TV has turned out great and it will be enjoyed by the family. I had to replace a couple of other tubes. Also the vertical linearity control was bad. I had a new one in the box it was a 5K ohm control. Hope you enjoy the article as much as I have. Thanks

Here is a picture of the finished Dumont TV: