Dumont RA-103 Project Redux

[Chris K]

What a dumb and fruitless time unless you count frustration and knowing your limitations as experience building.

The resistors came and I spent hours mounting and installing them. The area under the canohms seemed a perfect spot for bolting on these chassis mount resistors but I discovered the area was inaccessible from the top of the chassis due to the lower strap supporting the CRT. After making the appropriate changes to the layout plans, I finished the work and did a few other things most importantly, getting modern safety caps on the AC line. I buttoned everything up and began the testing. Turned it on...nothing. Panic. It was completely dead so I began investigating the AC hookup and the on/off switch and wiring. Long story short, I accidently clipped one of the wires going to the switch when I installed the caps. This chassis is a crammed full mess with hard, heat cured wiring twisted and hidden everywhere. I fixed it and began again. It powered on but my relief was short lived. When the relay closed there was no change in the amps being drawn. Obviously I had messed something up in the resistor install right? I spent several days tracing every circuit and checking the schematic over and over but I couldn't find any mistakes. I looked a square inch at a time over anything I might have moved or accidently disconnected or dropped solder on. Nothing. I even began putting together a detailed presentation for you guys with pictures of the work and the schematic detail etc. Maybe something in the relay got messed up again??? I started tracing voltages. In plane crash investigations there's something called "confirmation bias". You take an action and soon after, something goes wrong. Obviously it's something you did and you begin to see all subsequent events through the lens of your actions and focus just on that. The big picture is missed. The source of my problem with the RA-103? When I zip tied together some of the dozens of wires feeding up the side and across the chassis, I must have tied one too tightly. The wire from the choke to R285 snapped like uncooked spaghetti but couldn't be seen because it was hidden inside a wire bundle. Five minutes later it was fixed and the TV was working like it was before. Five minute fix after five days of fruitless troubleshooting over work that "obviously I must have messed up"! Well, technically I did mess it up but I lost an unbiased approach to the troubleshooting. Lesson learned...maybe. Can't make any promises on that one! More updates on progress, I hope, in the days to come now that I'm out of the self-induced quicksand.

[Chris K]

Are there 2 tuning dials for channel selection in various models of this tv? The brass gear on the back of my tuning dial stripped out at some point in its lifetime and I replaced it with the dial from my parts chassis and the 2 dials are completely different. The tv I’m servicing has the stripped gear and ascending channels when it’s turned clockwise. The parts chassis dial is the opposite…ascending channels when turned counterclockwise. I cleaned the tuner and the picture is so much better. Thought I was home free on this one

[Electronic M]

Originally Posted by Chris K

Are there 2 tuning dials for channel selection in various models of this tv? The brass gear on the back of my tuning dial stripped out at some point in its lifetime and I replaced it with the dial from my parts chassis and the 2 dials are completely different. The tv I’m servicing has the stripped gear and ascending channels when it’s turned clockwise. The parts chassis dial is the opposite…ascending channels when turned counterclockwise. I cleaned the tuner and the picture is so much better. Thought I was home free on this one

Not 2 but 3! There's 2 round dial RA-103s and a square dial. I've never owned a square dial but I have owned the other two. Yes one dial goes clockwise and the other counter clockwise. As I understand it the more common early round dial uses the tuner shaft for the knob shaft...which is bad since the portion inside the tuner is ceramic and tends to break if the user knob gets stuck on pressed on too hard. The later sets fixed that by using a separate knob shaft geared to the tuner shaft but at the expense of making the dial spiral the other direction and having to rotate the tuner superstructure 90 degrees.

[Alex KL-1]

Originally Posted by Chris K

What a dumb and fruitless time unless you count frustration and knowing your limitations as experience building.

The resistors came and I spent hours mounting and installing them. The area under the canohms seemed a perfect spot for bolting on these chassis mount resistors but I discovered the area was inaccessible from the top of the chassis due to the lower strap supporting the CRT. After making the appropriate changes to the layout plans, I finished the work and did a few other things most importantly, getting modern safety caps on the AC line. I buttoned everything up and began the testing. Turned it on...nothing. Panic. It was completely dead so I began investigating the AC hookup and the on/off switch and wiring. Long story short, I accidently clipped one of the wires going to the switch when I installed the caps. This chassis is a crammed full mess with hard, heat cured wiring twisted and hidden everywhere. I fixed it and began again. It powered on but my relief was short lived. When the relay closed there was no change in the amps being drawn. Obviously I had messed something up in the resistor install right? I spent several days tracing every circuit and checking the schematic over and over but I couldn't find any mistakes. I looked a square inch at a time over anything I might have moved or accidently disconnected or dropped solder on. Nothing. I even began putting together a detailed presentation for you guys with pictures of the work and the schematic detail etc. Maybe something in the relay got messed up again??? I started tracing voltages. In plane crash investigations there's something called "confirmation bias". You take an action and soon after, something goes wrong. Obviously it's something you did and you begin to see all subsequent events through the lens of your actions and focus just on that. The big picture is missed. The source of my problem with the RA-103? When I zip tied together some of the dozens of wires feeding up the side and across the chassis, I must have tied one too tightly. The wire from the choke to R285 snapped like uncooked spaghetti but couldn't be seen because it was hidden inside a wire bundle. Five minutes later it was fixed and the TV was working like it was before. Five minute fix after five days of fruitless troubleshooting over work that "obviously I must have messed up"! Well, technically I did mess it up but I lost an unbiased approach to the troubleshooting. Lesson learned...maybe. Can't make any promises on that one! More updates on progress, I hope, in the days to come now that I'm out of the self-induced quicksand.

In fact, this hobby sometimes is very challenging in various aspects... sometimes I found myself re-opening several times TV's due to several reasons...

[Chris K]

The gear on he back of the TV dial makes setup easy. I used the signal generator to output a crosshatch pattern on channel 4 and when it was perfectly tuned, I slipped the dial onto the shaft engaging the dial gear teeth with a lower reduction gear on the tuner and channel 4 illuminated by the dial light and the tuning bar through the opaque portion. I tried checking the accuracy moving the generator to channel 7 output and rotating the dial towards it and that's when I noticed the dial mismatch. I'm curious to know how the FM tuner works. Both dials spin in the same direction but at different rates, the FM dial turning much faster than the TV dial. There's a wide, opaque region on the TV dial labeled "FM" and my guess is by the time that area traverses the dial light, all of the FM stations on its dial will spin through the opening allowing tuning across the broadcast FM band. But none of this is going to happen until I find the appropriate dial or...dare I say...swap out the tuners. That's a daunting prospect for sure.

[Chris K]

Sound and picture aligned. I'm going to install the 12QP4 later tonight and see if it's any better but this is performing well. Soon I'll turn my attention to the cabinet. It has all the original brass screening on it and it's in pretty good shape. I have an original hinged metal back on the parts chassis and I got a decal set from RadioDaze.

[Chris K]

Started on the cabinet. The lacquer on the cabinet is so thick! I hate strippers and the mess they make so I used my scrapers to get the bulk of the finish off. Slow going but this is going to be a collection showpiece so I’m taking my time.

Image deleted...see below

[Tim]

Great progress. It can be tough along the way but if you persevere you will get there! If you go to page 21 of this Dumont Service News it shows the different dial configurations and part numbers. https://www.earlytelevision.org/pdf/...s_vol23-11.pdf

[Chris K]

Sorry for that gigantic picture. I uploaded it from my phone and I guess it chose the biggest version available. Here's a more reasonably sized group of photos.

[Chris K]

Originally Posted by Tim

Great progress. It can be tough along the way but if you persevere you will get there! If you go to page 21 of this Dumont Service News it shows the different dial configurations and part numbers. https://www.earlytelevision.org/pdf/...s_vol23-11.pdf

What a great resource Tim. I thought I had downloaded everything the ETF had to offer on Dumont TVs from this era. Thanks again.

[bandersen]

I'd switch to lacquer thinner at this point to get the last traces of finish off and even out the color. You don't want to sand through that nice veneer.

[Chris K]

Originally Posted by bandersen

I'd switch to lacquer thinner at this point to get the last traces of finish off and even out the color. You don't want to sand through that nice veneer.

Will do. I made a vow… no power sanding!

[Electronic M]

Swapping tuners on these isn't too hard...3-4 wires and some screws. I had to pull the tuner on one in the last year to get in and fix the antenna coupling cap that had went open... Until I did that I was wondering why the tuner was so darn snowy.

I favor lacquer thinner and steel wool for stripping...Seems to be the best combination of cheap fast and minimal cleanup.

[Chris K]

Originally Posted by Electronic M

Swapping tuners on these isn't too hard...3-4 wires and some screws. I had to pull the tuner on one in the last year to get in and fix the antenna coupling cap that had went open... Until I did that I was wondering why the tuner was so darn snowy.

I favor lacquer thinner and steel wool for stripping...Seems to be the best combination of cheap fast and minimal cleanup.

I got just about everything off the top and I've gone as far as I'm going to go. No sand throughs.



My big concern, for both stripping and finishing, are the angled vented sections that transition the top from the sides. I said earlier the brass screening here and on the bottom of the cabinet are pristine. When I do the front, I intend to remove the safety glass and surround and the brass ring around the tuning 6AL7. The screens are another matter. I can't see removing them (just the vents) but how in the hell am I going to spray a finish on this without getting lacquer all over these screens? Masking them would be very difficult but an option.

[bandersen]

How are the screens attached? Stapled on the inside? If so, pry they off with a screwdriver.