DuMont RA113 saved from becoming an aquarium! - Page 4 - Videokarma.org TV - Video

holmesuser01 · #46 08-16-2010, 08:57 PM

I think it will fit. A big public thanks to you.

Bruce

***Eric H*** · #47 08-16-2010, 08:59 PM

Cool, I'll ship it off to you tomorrow sometime.
You can pay me with PayPal when it gets there.

Someday I want to fill one of those flat rate boxes up with Lead wheel weights or Iron bars and see what they say when I want to ship it flat rate.

holmesuser01 · #48 08-16-2010, 09:10 PM

I'd sure hope my box of NOS 2A3's is not traveling under your lead wheel weight/Iron bar box!!!

I cant reply again until tomorrow afternoon. I gotta to to work in the morning, (kicks dirt with toe) I gotta go to bed.

holmesuser01 · #49 08-20-2010, 05:15 PM

It's now Friday.

The transformer has arrived. Thanks, Eric! I'll be sending you something on Monday.

Now for the fun task of identifying wire colors, and replacing brittle wires, painting, etc, etc...

It has begun.

Waiting for a Mouser catalog to arrive.

*Bill Cahill* · #50 08-20-2010, 05:50 PM

Quote:

Originally Posted by holmesuser01

I really appreciate the offer. I bet the 2nd 5V winding was for a 5Y3 rectifier, as alot of early sets had more than one rectifier.

Are the wires fairly well marked as to what they are? I dont want to blow up my set... I've replaced wires on a tranny before.

Bruce McGee

Nope. It's for damper winding.
Bill Cahill

*Bill Cahill* · #51 08-20-2010, 05:53 PM

Quote:

Originally Posted by jr_tech

By not using the 5V 2A winding you lighten the load by 10 watts... also the 6.3 of the RCA transformer is 9A, while the DuMont is designed for 7.4A, so that winding will not be running at full load, another 10.1 watts lightening of the load.
The additional draw at 770V from .240A to .260A is only 15.4watts, so the transformer could actually run cooler. DuMont tended to over-design, so the actual current draw in the B+ may be somewhat less than 260ma.
I would consider adding a couple of plate resistors in the 5U4 plate leads or one resistor in series with the input choke, to drop the extra 10 V.
Are the dimensions/bolt patterns similar?
jr

Don't connect your damper to six volt line!
You'll blow entire set!
That has hv pulse on it!
You MUST use that five volt winding the original used.
Bill Cahill

holmesuser01 · #52 08-20-2010, 06:11 PM

Dont Worry, Bill.

The DuMont has a separate filament transformer for the damper (a 6W4GT) on this set.

The 2nd 5v winding on the RCA transformer will not be used.

While I'm posting, any tips on getting the wire color to come up out of the filth on the current wires in this RCA transformer? I wet them with water and dried them with a rag. They still look mostly black.

***Eric H*** · #53 08-20-2010, 06:20 PM

I was hoping perhaps the colors might be more visible inside the transformer, or at least they might be numbered.

Resistance checks should identify the primary's, wouldn't they have the highest resistance?

I think they were the smallest pair of wires but I can't remember.

holmesuser01 · #54 08-20-2010, 06:32 PM

Im going out to dinner tonight. I'm going to pull the shell off the transformer tomorrow...carefully.... And we will see what we can see....

*Bill Cahill* · #55 08-20-2010, 07:42 PM

That black color is tar.
I'd check voltages, first.
Hint.
Five volt colors for 5U4 should be yellow.
Plates, red with yellow tracer.
B- brown with black tracer.
primary: both black.
Regular six volt two green.
Other six volt would have been two blue.
You could disconnect filament pin from cathode, install a 6AX4, and, use that.
Bill Cahill

wa2ise · #56 08-21-2010, 12:03 AM

Quote:

Originally Posted by holmesuser01

Dont Worry, Bill.

The DuMont has a separate filament transformer for the damper (a 6W4GT) on this set.

The 2nd 5v winding on the RCA transformer will not be used.

You could place that 2nd 5V winding in series with the primary, to add approx 5V to the 120V primary's rating, to compensate for today's higher voltage powerlines. You'll know if you got the phasing correct if the old primary has approx 5V less voltage than your powerline has. And if the various secondaries produce about 4% less voltage than before. If they go up in voltage, reverse the 5V secondary lead connections.

holmesuser01 · #57 08-21-2010, 09:52 AM

Quote:

Originally Posted by Bill Cahill

That black color is tar.
I'd check voltages, first.
Hint.
Five volt colors for 5U4 should be yellow.
Plates, red with yellow tracer.
B- brown with black tracer.
primary: both black.
Regular six volt two green.
Other six volt would have been two blue.
You could disconnect filament pin from cathode, install a 6AX4, and, use that.
Bill Cahill

The blackness is not tar. In fact, the wires are just cooked pretty good. We got the cover off, and I'm getting an expert with colors (my sister) to help with the ID. I think I found the primary wires. Im absolutely NOT connecting anything to power until I know whats what. Ohm meter? I love mine.

I wasn't sure about the wire colors. I've replaced a few transformers in old Fender, and Magnavox amps, and the color codes were the same as what you said.

All of the tubes in the set are now testing good. Now, we wait for the Mouser catalog. I have a few capacitors laying around from other projects that I can replace in the meantime.

This may take some time. I'm having to go to work this afternoon and replace a $1000 4,000 watt xenon lamp in a projector. Happily, for job security, I am the only one there that knows how to do it.

holmesuser01 · #58 09-30-2010, 08:48 AM

Progress!

I have a complete RA111 chassis on hand for parts. It uses the same power transformer as the RA112/113.

My first Mouser order got cancelled, due to alot of substitutions on their part. Not a problem, though.

I will install the transformer and leave out the rectifier for now. Replace the 7-8 electrolytics, and go from there. I've gotten alot of PM's about DuMonts and quality.
I look forward to seeing the soft glow of the chassis... minus B+ for right now.

The RA111 chassis has a fuse socket mounted on the chassis. It is much newer than the chassis. I will be fusing my set, too. I sure dont want anything like this to happen again. 2010 has been my year of bad power transformers. But, its also been good as I have found replacements for them. I have my friends here at VK, and ARF, to thank for this!

More to come, as it happens...

holmesuser01 · #59 10-04-2010, 06:07 PM

Pulled the old transformer and rectifier tube socket as an assembly today. Found one side of the rectifier tube socket had been very hot at some point and had broken away. Installed in the set, I couldn't see this side of the socket. Thankfully, the doner RA111 has the same transformer/rectifier socket mounting so I reinstalled the transformer using this mount. While in there, I found a single wire that had almost no insulation that was cooked thoroughly. Apparently this wire had a long time working while damaged in this set, as there is rust in several places along its run. Turns out that it runs from the power interlock to the back of the switch.
I attached the new wire to the end of the old one, and gently pulled it through under all the other wiring from the switch back around the side of the rectifier tube socket and up to the interlock. It is working.

I'm not applying any B+ anywhere on this set until I get a load of capacitors replaced. I did turn on power thru my variac just to see what it would do. It powers up fine, all tubes are lit, so I left it running this way for a little while just to let the chassis get somewhat warm, and to see if this transformer is OK, which it is. I have to re-solder the transformer filament winding lead after I move some wax caps out of the way. Someone in the past has done some not-so-pretty repairs in the past around this area of the set. I'm fairly sure that this transformer has been replaced before. The one I removed has the same part number as my replacement does. I've found some snipped wires at solder connections with the same colors on them as what the transformer has. I sat here looking at the tubes glowing in the chassis, when...

Suddenly, POP!

I looked quickly at the chassis while fumbling for the switch on the variac. I watched one of the 2 flat capacitors connected to both sides of the power line to ground slowly open up like a clam. Cut power, and cut it out of the circuit along with the other one. The Riders schematic doesent show these caps, so I will leave these off, unless instructed otherwise.

So, here we are. It lights up. All the controls are cleaned except for the tuner itself.

It's all ready to run after the cap replacement.

holmesuser01 · #60 10-04-2010, 06:28 PM

Some new pictures of the switch wiring, the front of the tuner dial, and some of the transformer with most of its wiring finished, especially on the rectifier socket. You can see the exploded capacitor, and its undamaged, but very warm sister, both since removed.

Also, in the first pic, you can see the routing of the very yellow replacement wire snaking thru the chassis under everything else there. Notice the rust. The wire I removed was thoroughly cooked with very little insulation left.