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 Post subject: help me understand why UV199 behaves this way?
PostPosted: May Sat 29, 2010 6:32 pm 
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I have a UV199, maybe, that has an internal problem, but I don't understand what it is. I suspect the tube has been separated from its base at some point. The base is stamped Radiotron UV-199, and appeared to have no filament continuity. It turns out the filaments were not connected to the right pins for a UV199. I boiled the base off and found what appears to be original cement, the dark bubbly/crumbly stuff you typically see. Anyway, I used jumpers to the tube tester (Stark 9-66, like Hickok 570) to see if the tube tests okay before putting the base back on. The tube shows no shorts.

When the filament is lit, I can see enough to make out a filament running straight through a cylindrical grid and plate arrangement, and from what I can see it looks very similar to other UV199s.

With 3v on the filament, there is pretty good output similar to another good UV199, but I noticed that changing the grid bias makes absolutely no difference in output. I can disconnect the grid jumper with no effect. The jumpers are good, I've already scraped the bare wires clean for reliable connections, so this tells me there is an internal problem.

Just for fun, I grabbed a couple of good UV199s and tried to duplicate the behavior. An open grid makes the Stark meter try to swing negative. Shorting grid to plate or grid to filament drops the output to about 15% at most. Shorting grid to the other filament drops output even more. I cannot come close to seeing the same behavior as this mystery tube.

Any ideas what might be happening? I know the tube is toast, I'd just like to understand WHAT is happening.

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PostPosted: May Sat 29, 2010 8:09 pm 
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Maybe there is a break in the grid connection somewhere Probable place is in the press where the upper nickel wires are welded to the dumet. I recently had a Marconi DET 1 with a good-looking filament which would not light. After exhausting the regular options, I finally touched a high voltage sparker to one of the filament pins, and a tiny spark could be seen jumping the break inside the press.

Jim Cross


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PostPosted: May Sat 29, 2010 8:42 pm 
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Thanks, that makes sense, probably is where the problem is. I am still puzzled as to why I cannot disconnect the grid of a regular tube and get anything like the same effect.

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PostPosted: May Sat 29, 2010 10:00 pm 
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Location: LONG BEACH CA.( 90808}
what radio are you trying it n Jewel.

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 Post subject:
PostPosted: May Sat 29, 2010 10:38 pm 
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Hi Jewel,

Nothing now, I'm simply trying to make a good UV199 behave on the tester like this one, as a learning exercise.

It came in a Radiola 26 a couple of years ago. During that restoration I obtained some UV199s to get it working and have ended up with the six in the Radiola, 2 more reasonably good spares (although one is quite microphonic), 4 more that are weak and beyond further rejuvination, and finally this dud.

I've been pulling together extra tubes (stuffed in the sock drawer and boxes) and making notes about their Stark tester readings, just so I know what is here next time I'm rummaging around for something. During the process I found two 01As marked as open filament. One needed reheating/solder of a pin, but still tests weak, and the other turned out to be mis-wired to its base (the grid and a filament were swapped!). Once I realized that, it was a simple fix and now measures pretty well. It'll probably go into a Crosley that currently has two "display" tubes.

I'd hoped to have similar good fortune with this UV199, but there doesn't seem to be much hope for it as a triode. For now the bottle and base are still separated.

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 Post subject:
PostPosted: May Sat 29, 2010 11:42 pm 
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The grid may have internal leakage to one of the other elements, enough to keep it biased at some point.


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PostPosted: May Sat 29, 2010 11:57 pm 
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Location: LONG BEACH CA.( 90808}
you need to remember these old tubes are real old the fill may become brittle over tlme I have some tubes that check good on tube tester but wont wont work in a radio the 01A's and 199 tubes will do that Jewel

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PostPosted: May Sun 30, 2010 1:45 am 
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The getter may have been flashed onto the press.

BTW: '01A's can be rejeuvenated too.


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PostPosted: May Sun 30, 2010 3:46 am 
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Hmm I just bought a 327 from eBay, and there is about 10 megs between each of the pins. Nothing at all LOOKS like it is shorted, and the tube does look NOS. Wish I had a tester to give it a check out.

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 Post subject:
PostPosted: May Sun 30, 2010 4:13 am 
Silent Key

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Location: Sandpoint, IDAHO 83864
I have a globe 46 tube that shows the same thing. It is a National Union and the number on it is NU-46. However it is not a problem with the tube itself, but the base.

I don't know what sort of composition they used to make the black base of the tube with, but I can take an ohm meter and measure a couple megohms across any point on the base. Some spots are worse than others. And measuring from the control grid to the plate or screen grid, it measures about 2 megohms.

That would drive a person to the nuthouse wondering why the control grid was going positive after replacing a coupling capacitor. I think the only thing the tube had going for it was it probably came out of a set with Class B output. That would require transformer coupling and the low resistance of the transformer secondary winding would swamp out the tube leakage.
Curt

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 Post subject:
PostPosted: May Sun 30, 2010 4:49 am 
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Curt,

I bought a large estate of tubes and other Ham ephemera in '79. As I perused through my treasures I found a number of '10's and '50's with blistered bases and crossed saw cuts on the bottom of the bases. I gave the fellow a call about the tubes and he told me that was common practice for Hams to cut the bases. The Bakelite didn't like RF and the bases would conduct and blister around the pins. Cutting the base greatly extended the rf path and made the tube usable, even after blistering.

Is there a possibility the 46 saw RF service?

Chas


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 Post subject:
PostPosted: May Sun 30, 2010 12:23 pm 
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Not likely the base was installed wrong.
The grid had to be touching the filament and welded itself, opening up the existing filament run.

I've seen lots of these tight fitting cylindrical element type tubes short. I've repaired a few as well.


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 Post subject:
PostPosted: May Sun 30, 2010 2:05 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
Chas- I am aware of hams of yesteryear would make hacksaw cuts to the tube bases to reduce losses, especially when trying to get the tubes to operate on some of the higher bands.

On that NU-46 there is no sign of the base ever overheating. There is no blistering or discoloring of the material. It simply shows leakage across the base. At one time, I thought the inside of the base may be damp, so I sat the tube on top of the refrigerator where it is quite warm. I forgot about it and the tube sat up there for close to two years. When I found it again, I checked it, and it still had that leakage.

So I think it was simply a foul up in the mixing of the stuff that forms the base of the tube.
Curt

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(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: May Sun 30, 2010 2:08 pm 
Silent Key

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Location: Sandpoint, IDAHO 83864
I also wonder if there was some attempt to re-base the UV99 tube in discussion? Maybe to fit a UX99 socket? One thing a few people don't understand is that the pinout of the UV and UX99 tubes is also different.
Curt

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 Post subject:
PostPosted: May Sun 30, 2010 2:25 pm 
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DING DING DING!!! The bell goes off in my head. Thank you for that! Indeed, the UV199's filament is now returning through the grid. The original return is severed and connects to nothing. This also explains why the tester did not see any shorts. Makes perfect sense.

Curt, I had the same thought, I wondered if someone had tried to re-solder the tube and just assumed the wrong pinout. The thing that turned me away from that is that the pins seemed to be tin, not easy to melt like solder, and when I boiled the base off I see no evidence of new glue. But, it is certainly possible.

The above assumption of a grid short also gives a possible explanation of why I cannot take a good UV199 and connect the grid to the filament at the tube base to get the same results. Doing so does not place the grid at the same potential (relative to the filament) as an internal short, because when connected at the base, there is some additional filament resistance in the way.

Maybe with pure dc test signals I could more closely duplicate the dud tube with a mis-wired good tube, but that is a project for another day.

Thank you ALL!

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 Post subject: Re: help me understand why UV199 behaves this way?
PostPosted: Feb Sat 24, 2018 1:34 am 
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These old threads really help. I purchased my first UV-199 and I tested the filament and it tested open. However I did get continuity from another pin. I assumed some kind of short. This old thread taught me about the different pin connections of a UV-199 from the UX-199. Thanks to all those who contributed to this "vintage thread".

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 Post subject: Re: help me understand why UV199 behaves this way?
PostPosted: Feb Sun 25, 2018 1:16 pm 
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Location: Cedar Rapids, Iowa, USA
There is another trap to beware of. There were two kinds of UV-199. The "official" one (RCA) had the nub pins, and was later called the small base type. Later, other manufacturers created what they called the large base UV-199. It had the more "standard" UV base with the short pins. I have some examples, and have seen several old ads for them, but have never seen a tube manual with them. I think they were made with the UX-199 pinout 4D so the older radios with 201A's could be re-tubed with UV-199's and run from dry cells instead of the older storage batteries. There were also adapters made so the small base tubes could be used the same way.
I am sure RCA was not keen on keeping old radios working with new tubes. They would much rather sell a new radio and new tubes.

--edit: the small-base V99 as listed by RCA and GE used wiring diagram 4E. The X99 used diagram 4D, same as the 01A.


Last edited by tubemaster on Feb Wed 28, 2018 12:34 pm, edited 1 time in total.

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 Post subject: Re: help me understand why UV199 behaves this way?
PostPosted: Feb Tue 27, 2018 9:45 pm 
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No doubt your right tubemaster, corporations never change! :lol:

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