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 Post subject: Tube tests good, but does not work in the radio
PostPosted: Sep Mon 20, 2021 6:14 pm 
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The tube is a UV-201A. There are no visible markings on the base or glass, so the brand is unknown. It tests GOOD+ (as a 201A) on an Espey 105 (i177 type), Hickok 600A, and Navy TV-3B-U. The tube was tested for gm, shorts, and gas - no problems found. The radio is an Atwater Kent model 12C 4910 breadboard. The tube does not work in any position in the radio, although is does light up. How is this possible?

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Mon 20, 2021 6:24 pm 
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Some other area of the radio is defective????

Rich


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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Mon 20, 2021 6:48 pm 
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Rich, W3HWJ wrote:
Some other area of the radio is defective????

Rich

The radio works with many other good tubes in my UV/UX 201A collection plugged into any of the 6 possible positions in the radio. Since it is not marked, it has only been TESTED as a 201A. I suppose it is possible that it is NOT a 201A. It is definitely not a UV 200A since it has the typical flashing pattern.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Mon 20, 2021 9:39 pm 
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Corrosion on the grid pin or possibly the plate pin of the tube. The contact point in the tube testers is different than the contact point in the receive sockets.

Norman

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Mon 20, 2021 9:48 pm 
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Braithwaite wrote:
Corrosion on the grid pin or possibly the plate pin of the tube. The contact point in the tube testers is different than the contact point in the receive sockets.

Norman
Exactly, The tube tester sockets contact the sides of the pins, the radio contacts the tips of the pins. Clean all that grey oxide off of the tips of all the tubes and use a stenographers eraser (gritty rubber) to polish the tangs of the tube sockets...

GL

Chas

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Last edited by Chas on Sep Tue 21, 2021 3:01 pm, edited 1 time in total.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Mon 20, 2021 9:58 pm 
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I have wondered how a tube that tests good at audio frequencies in a tester (60 hz) might still be lossy enough to function poorly or not at all when used as an amplifier in an RF stage. Does this logic hold water?

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Tue 21, 2021 7:20 am 
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Y'all need to remember that a Hickok tester, any Hickok tester, tests a tube under very limited conditions. I haven't worked with vintage tubes, but I have no problem believing that a tube would test good but not work in the radio. I do know that a '60s era 6C4 can test good, work in an AF amp, even work in an RF amp, but not work in a receiver LO.

The ultimate tester is the circuit the tube came out of - as long as the circuit itself is good.

John


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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Tue 21, 2021 2:18 pm 
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The usual cause for a tube that tests good but fails to work in a receiver is a weak cathode. Tubes most susceptible to this are oscillators, converters, and power output tubes. Reason is, testers limit the cathode current to a low "average" value to ensure you do not damage the tubes by testing them. But circuits like oscillators and converters depend on the peak current currents cathodes can deliver, not low or average values. In audio output stages and television deflection circuits this is true too. So under those circumstances a tube may test good but prove unsatisfactory in the equipment.

However, in this case the OP tested the tube in every socket in the radio, which would include both audio and RF stages, as well as the detector. It's a TRF, so no oscillation or peak currents being drawn there. If the tube has enough emission to check OK on the tube tester, then it should be capable of working in at least one of the stages in the radio. It is possible that a malformed or distorted grid could cause a tube to oscillate in an RF socket, but then it should still work in the detector or audio sockets. If the tube had no Gm, but it passed the shorts/leakage/gas test, then what was the I-177 tester reading?

Thing is, in an Atwater Kent breadboard the tube sockets are bayonet types, using the locator pin to hold the tube in place. Contact is made with the bottoms of the pins. This is different than the 1940s tube tester mentioned, which has standard Bakelite sockets with side pin contacts. Now Chas and others have already mentioned that the bottoms of the pins have to be clean and making good contact in order to work in the radio, but not necessarily in the tube tester. I would go a step further and check the lengths of the pins; if one is shorter than the others by a small amount, it won't make contact with the socket either.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Tue 21, 2021 2:50 pm 
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Are the pins of that generic UV-201A actually making contact in your AK set. Keep in mind, the contact points on a tube tester is along the sides of the tube's pins. The contact point on the AK receiver is at the tips of the tube's pins. Could it be that one or more of the pins aren't making proper tip contact due to shortness of the pins or quality of the old solder at the tip of the pins?

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 1:24 am 
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I use a home-built UV (short pin) to UX (long pin) adaptor socket with a cable that plugs into the 4-pin tube tester socket. So both the tube testers and the radio are contacting the bottom of the pins. I also have cleaned the radio contacts. I think there is something wrong with the tube, since in one of the testers the tube almost pins the meter on the "English" scale. The gm readings are also very different from tester to tester. I plan on ditching the tube, and to rely on testing in an actual radio. I tested my box of 201A tubes that tested weak or slightly weak. More that 3/4 of them worked perfectly in every socket in a AK Breadboard 12C. And a few in my GOOD box (tested) worked but required significant increase in filament voltage in order to get decent reception. None of my tube testers have been professionally calibrated. Only the filament, plate, screen, and bias voltages have been checked.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 3:09 am 
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Sounds like a gassy tube. Did you test for gas? It will cause a tube to test high but the tube will not work. A small amount of gas will not illuminate between elements.

Norman

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 3:14 am 
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processhead wrote:
I have wondered how a tube that tests good at audio frequencies in a tester (60 hz) might still be lossy enough to function poorly or not at all when used as an amplifier in an RF stage. Does this logic hold water?


I used to replace the IF stage ( 70 MHZ) tubes in Sperry radars and watch the tuning meter or my Oscope to see if the signal got better , my boss would check them on a Sencore tube tester and put them back in boxes and on the shelf .I would go out on a service call and try tubes in the IF and the signal got worse ( and picture ) , so i threw the old ones away before coming back to the shop .

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 7:27 am 
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Oh, it is horror with the 6GH8As... :shock:

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 1:41 pm 
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Braithwaite wrote:
Sounds like a gassy tube. Did you test for gas? It will cause a tube to test high but the tube will not work. A small amount of gas will not illuminate between elements.

Norman

Yes, the tube was tested for gas and shorts in the Hickok 600A and TV-3B-U testers. There was essentially no change between GAS1 and GAS1+GAS2 on the tester. Due to tube flashing, I could not observe if there was any sign of gas (blue glow) between elements. But I may not be performing the gas test correctly. On the TV-3B/U Navy tester (Hickok) it says to press GAS1 and adjust Bias control so that the pointer is on the first LARGE division mark on the 3000 scale. So I set the GAS1 point to 500 micromhos. Then hold down GAS1 and press GAS2 - the pointer must not move more than one SMALL division.

I think that it is significant that OTHER tubes in my stock that test GOOD work, but perform poorly unless the filament voltage on the radio is increased. The tube in question does not work regardless of the filament rheostat position on the radio.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 3:44 pm 
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So have you any other radios that use that type? Otherwise you could set up a bench experiment like we did in high school to demonstrate triode function. Need something like power sources, a milliammeter and a resistor or two. See if there is emission, if there is plate current, and if variable grid bias will control the plate current. And you have other tubes for comparison.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 5:29 pm 
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Getter flashing patterns are a 100% unreliable way of determining what kind of tube it is. According to General Electric (which made the tubes for RCA), the UV200 and UV201 were identical in every respect, except the UV200 had a trace of argon gas at very low pressure introduced into it before it was sealed.

If you have assured yourself of good connections to the pins then it is very likely what you have is a UV200 there. It sounds to me like every tube tester you tried applies AC to the tubes under test, which would tend to prevent the tube from ionizing and blocking signals completely. On DC in the radio it could be doing just that. Unfortunately the gas in a UV/UX 200 is not intended to be ionized, and if it happens by accident, it de-sensitizes the tube permanently. This is why the plate voltage limit was not supposed to exceed 22.5 volts. (The later UX 200A contains a hard vacuum and is more forgiving as long as its plate voltage is kept under 45 votls). So if the tube has been tried on various tube testers and in various sockets at higher voltages it is probably not going to work as a 200 or a 201, though it may still be capable of some amplification at lower plate voltages.

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Wed 22, 2021 5:32 pm 
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Dave are you familiar with this practice?

http://www.nostalgiaair.org/References/ ... lash08.htm

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Thu 23, 2021 12:28 am 
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If I read your post right, you said you were operating the suspect tube at the end of an extension cable that also changed the socket type. Using any type of extension cable is pretty much guaranteed to make an RF amplifier inoperable, too much capacitance. What it would do to a detector or AF amplifier is harder to predict but it wouldn't have any effect on a tube tester. Can you make an adapter that is very small, say 1 inch or less?

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Thu 23, 2021 1:04 am 
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Jim Mueller wrote:
If I read your post right, you said you were operating the suspect tube at the end of an extension cable that also changed the socket type. Using any type of extension cable is pretty much guaranteed to make an RF amplifier inoperable, too much capacitance. What it would do to a detector or AF amplifier is harder to predict but it wouldn't have any effect on a tube tester. Can you make an adapter that is very small, say 1 inch or less?

The extension cable is only used for TUBE TESTERS. The radio accepts both UV and UX tubes (AK 12C 4910 Breadboard).

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 Post subject: Re: Tube tests good, but does not work in the radio
PostPosted: Sep Sat 25, 2021 7:52 am 
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battradio@ wrote:
processhead wrote:
I have wondered how a tube that tests good at audio frequencies in a tester (60 hz) might still be lossy enough to function poorly or not at all when used as an amplifier in an RF stage. Does this logic hold water?


I used to replace the IF stage ( 70 MHZ) tubes in Sperry radars and watch the tuning meter or my Oscope to see if the signal got better , my boss would check them on a Sencore tube tester and put them back in boxes and on the shelf .I would go out on a service call and try tubes in the IF and the signal got worse ( and picture ) , so i threw the old ones away before coming back to the shop .

Yes, the radar business be a little, well, a lot, finicky. When I was working HAWK maintenance in the US Army, I spent a little while working on PARs. The PAR (pulse acquisition radar) has two identical IF strips: one for the main channel and one for the side lob canceler. In addition to setting identical gains in both channels (pretty simple), the tubes in each stage WERE SUPPOSED to be gain matched to the corresponding tube in the other channel. I kept 8 to 10 matched pairs on hand and replaced the corresponding pair when one failed.

We lacked the test equipment to really tell if it made a difference, but I always thought that the closer you can get to nominal operation, the more slack you have when something does go a little bit wrong.

John


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