The Family DuMont

[wa2ise]

Originally Posted by CaryLee

Mystery Tube! That black metal tube center-left in first photo has all the numbers rubbed off..

You can usually find the tube number embossed in the metal part that surrounds the octal plug part of the tube.

[CaryLee]

Originally Posted by wa2ise

You can usually find the tube number embossed in the metal part that surrounds the octal plug part of the tube.

Thanks. I took a look but don't see any number there. It's a JAN military surplus tube, apparently Ken-Rad..Ken is visible, "Rad" is worn off. The only numbers on it are a "V4", and "SC961A", but I haven't found any cross-reference to that number. There is also a barely visible "2" like it's the end of the a number, and cross reference to a 6AC7 is an 1852, so that's a possibility. Visually, it does appear to be the correct 6AC7, and the heater pinouts match, so I'm going to figure that's what it is for now since I don't have any reason to think someone would have put the wrong one there. It's the only metal tube in the TV, and apparently the 6AC7 is only available as a metal tube. I've now seen photos of the embossed number like you mentioned, and this tube definitely doesn't have one.

[CaryLee]

Recapping has begun! No turning back now....

[David Roper]

Originally Posted by CaryLee

apparently the 6AC7 is only available as a metal tube

A vanishingly rare 6AC7GT was produced. There is at least one vendor selling them for a very reasonable price; it's tempting to get one or two for experimentation to see if they are at all suitable for use in TVs.

[holmesuser01]

Your set must be an early version. My RA-113 has a 7 pin miniature tube in that spot.

I've got a couple of used 6AC7 GT's here, according to my lists. Don't know if they are good or not.

[CaryLee]

Originally Posted by holmesuser01

Your set must be an early version. My RA-113 has a 7 pin miniature tube in that spot.

I've got a couple of used 6AC7 GT's here, according to my lists. Don't know if they are good or not.

According to the SAMS Photofact, production changed bulletin, your set might be earlier than mine. SAMS says: "To accommodate tube availability the video amplifier tube, V9 was changed to a type 6AC7. The tube socket wiring was changed when the 6AC7 tube was used." (I'm no expert, but that last sentence seems kind of obvious...since the tube it replaced was a mini glass tube and the "new" replacement uses an octal base.)

The bulletin doesn't give dates, but serial numbers and some chassis codes. Apparently this change was made on the 112A at #1232254.

The bulletin also seems to indicate that the change was only made on the RA-112A. There's nothing in the SAMS production changes bulletin that says it was ever changed in the RA-113. Don't know why they'd change it "to accommodate tube availability", and not change it across the board.

[ChuckA]

Originally Posted by CaryLee

Thanks. I took a look but don't see any number there. It's a JAN military surplus tube, apparently Ken-Rad..Ken is visible, "Rad" is worn off. The only numbers on it are a "V4", and "SC961A", but I haven't found any cross-reference to that number. There is also a barely visible "2" like it's the end of the a number, and cross reference to a 6AC7 is an 1852, so that's a possibility. Visually, it does appear to be the correct 6AC7, and the heater pinouts match, so I'm going to figure that's what it is for now since I don't have any reason to think someone would have put the wrong one there. It's the only metal tube in the TV, and apparently the 6AC7 is only available as a metal tube. I've now seen photos of the embossed number like you mentioned, and this tube definitely doesn't have one.

Military tube then the number missing is VT-112


Chuck

[CaryLee]

Originally Posted by ChuckA

Military tube then the number missing is VT-112


Chuck

a-HA! Thank you!

[CaryLee]

Yesterday was a marathon recap day! I'm not a very fast solderer, I have big hands, a 30 watt iron, and can't friggin' see close up through my glasses anymore (I'm resisting bifocals). And some of those caps are in VERY tight spots, particularly the two that were in the metal box in one corner of the chassis..it took forever to finagle those out and then in again.

I still have the HV section to tackle today, but I feel I'm on the downhill side!

Here's a couple noteworthy events:

The parts list in the SAMS photofact appear fairly accurate. In general, in replacing the paper caps, I ordered one or two spares of each, in case I screwed up and ruined some, and that's about what I ended up with. EXCEPT the .05 value. I ordered 11 of them, and I'm pretty sure I ordered at least two spares and maybe three, because it uses far more of them than anything else..and I only have ONE spare left.

I will say this: I didn't take into account the productions changes bulletin when I ordered caps, primarily because I didn't think of it until after the order was placed, so that could account for coming up "short"...glad I ordered extras!

There are a couple other values that I have extra leftovers of, and that might coincide with the "shortage" of .05's.

MOST notable is that I came up one short on 10uf 25 volt electrolytics. There is only one listed on the parts list (I didn't order any spare electrolytics, primarily because of expense, and not being familiar enough to know what I might use in the future, and I might lose them down the road anyway...you should see my shed..I figured they're a tad more durable with their aluminum housings, too) Turned out there's one in the "main chassis", and there there's another one "hidden" inside the aforementioned metal box in one corner of the chassis. The SAMS photofacts photos show it there, with the cover off the box, but there is nothing at all denoting it's existence. None of the usual arrows corresponding to SAMS location numbers point to it. Seems it was missed somehow. I didn't find it in the production changes bulletin either. Luckily it's a value that our local Radio Shack appears to stock, for a couple bucks, so I'll go get one today and get it in there.

Evidence of prior replacement caps: In one case, location C2 on the SAMS, calls for a 50uf 150 volt electrolytic. What was actually there was a 16uf 150. It's listed as a "filter". Don't know the result of such a change, but it's back to the value as listed in SAMS. I'm sure it was an early replacement, as it was soldered to a cut "pigtail".

There was also a couple older plastic caps in there. A HUGE Mallory .5 "Plascap" and a plastic Sprague.

Pretty much every old paper wax coated caps was "gooey". I saw in a previous write up by someone that they had to get the residue off their hands with Boraxo. I keep Boraxo around too! Works wonders!

I did not "restuff" any of the old cardboard or aluminum caps, but did leave them in place for aesthetics. Frankly, I'm not completely confident in my abilities, I've never worked with multiple can caps before, and figured if something goes haywire in the power up, I wanted to be able to see, smell, and hear what was going on...and having everything out in the open will make replacement in that case easier.

Here's a photo of what appears to me to be a couple of obvious failures:

[ggregg]

Been my experience that some of the worst looking caps still work. You just never know.

You didn't leave the old caps in circuit, did you?

[CaryLee]

Originally Posted by ggregg

Been my experience that some of the worst looking caps still work. You just never know.

You didn't leave the old caps in circuit, did you?

No. I cut them out and replaced them all, except for the one electrolytic I came up short on..I soldered it back in as a "placeholder" until I can get a new one today.

I did leave the aluminum cans in place, so I assume their "grounds" are still attached to the chassis. (Except for one that is attached to an insulating board which seems to have a separate ground as part of another circuit, C6 in the SAMS: Decoupling and Vert. Amp. Cathode, so it's ground is still connected to it's circuit) But the positive leads were cut loose and soldered to the positive leads of the new electrolytics.

Would there by any problems associated with that? Should I "gut" the old aluminum can caps?

[Phil Nelson]

The appearance of an old capacitor tells you basically nothing unless it has catastrophically exploded.

Caps may look perfect on the outside and be utterly worthless on the inside. Conversey, as ggregg noted, an old cap can also look awful on the outside -- all grungy, dripping, etc. -- and still be operational.

It's like finding a 60-year old car in the barn and trying to guess the condition of its engine by inspecting its paint job. Not a reliable guide

The failure rate for 60-year old electrolytic and paper capacitors is so high that you will save a lot of time and grief if you simply replace them all.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[CaryLee]

Originally Posted by Phil Nelson

The appearance of an old capacitor tells you basically nothing unless it has catastrophically exploded.

Caps may look perfect on the outside and be utterly worthless on the inside. Conversey, as ggregg noted, an old cap can also look awful on the outside -- all grungy, dripping, etc. -- and still be operational.

It's like finding a 60-year old car in the barn and trying to guess the condition of its engine by inspecting its paint job. Not a reliable guide

The failure rate for 60-year old electrolytic and paper capacitors is so high that you will save a lot of time and grief if you simply replace them all.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Howdy Phil!

So a cap with both ends bulged out can still be, technically, "good"?

Guess I should save those for spares!

[CaryLee]

Photo of finished recap..except for the one electrolytic next to the transformer center-left, which is the one I came up short on because the SAMS parts list only indicates one 10uf 25 volt cap used. That one will be replaced later today, "Radio Shack be willing and the creeks don't rise". The other one is upper far right, normally covered by a metal box. It's tucked in behind the upper end of the yellow replacement cap up there. I put the one I had up there because it looked tough to get to, and it was, without a doubt, the most frustrating cap to install on the entire set so far.

If some of the electrolytic replacement looks a bit "ham-fisted", well, "c'est la vie", once the chassis is back in the set, I won't be able to see 'em, even from my house!

[Kevin Kuehn]

Lookin' good. I used to could see up close at a microscopic level back in my 20's, now I need to rely on a couple different strengths of reading glasses that I pick up at the grocery store.