EYEBALLING A BAD TUBE?

[Stellasstillarat]

Is it possible to eyeball a bad (audio/final) tube?. If so I'm assuming I should key up and add audio while I'm looking at them. What might the tube look like if it's weak or bad. I don't have a tube tester but I know just because a tube is lit doesn't mean it's good..

 

[Captain Kilowatt]

I deleted the other thread you started with the same topic BTW.

No you cannot normally tell a tube is bad just by looking at it......usually. Sometimes you can however depending what is wrong with it. If it gets REALLY red fast it may ne bad but it could be other components making it operate hard. A weak tube cannot be seen but is usually niticed by low output and/or distortion.Subbing out a known good one will tell. If there are holes in the plate however chances are pretty good that it is bad.

 

[Tallman]

Actually you can spot a dead tube with a bad heater, or a gassy tube because it arcs.
A gassy tube that has burnt out looks like it is frosted on the inside.
Captain Kilowatt is right about weak tubes, no visual cues.

 

[357magnum]

Ahhh ... Remember years ago you could walk into some stores an they had tube checkers ? I was lucky enough to find a brief case sized one at a garage sale about 25 years ago it even had the instruction booklet I think I paid $3 for it , it has come in handy over the years !

 

[Captain Kilowatt]

Actually you can spot a dead tube with a bad heater, or a gassy tube because it arcs.
A gassy tube that has burnt out looks like it is frosted on the inside.
Captain Kilowatt is right about weak tubes, no visual cues.

Obviously a bad heater can be seen......or is it just a bad connection going to the socket? A lot of tubes will not arc even if they are gassy unless they are power tubes. Small receiving or audio tubes may not arc at all. They may show a little green or purple glow however if they have a really high plate voltage.

 

[Beetle]

Hold the tube six feet or more above a bare concrete floor. Drop it.

If it breaks, it was good.

 

[wavrider]

Take the tube to your local tech. HE or she should have a means to test a tube. Have it tested then EYEBALL your hard earn cash floating away as you purchase NOS tubes that have not been manufactured in 30 years.

Then ask yourself WHY are you f,ing around with old sweep tube stuff,???????

 

[Atlasta]

Gassy tubes will sometimes glow a bit blue under load. I've read several articles on how to fix a gassy tube but IME it's just easier to replace them.

As always, Google is your friend:
https://www.google.com/search?num=1....6.0....0...1c.1.58.serp..5.4.797.pLTUe5yewuk

 

[Captain Kilowatt]

Take the tube to your local tech. HE or she should have a means to test a tube. Have it tested then EYEBALL your hard earn cash floating away as you purchase NOS tubes that have not been manufactured in 30 years.

Then ask yourself WHY are you f,ing around with old sweep tube stuff,???????

I wasn't aware the type of tube was mentioned.

 

[Tallman]

WaveRider said, "Then ask yourself WHY are you f,ing around with old sweep tube stuff,???????"

Because tube units sound better and are not as finicky as transistors.

 

[wavrider]

I agree tube units sound better.

They are fun to use, BUT unless you know how to maintain them and are WILLING to invest in the test equipment required to maintain them then my statement stands.

It is more expensive to operate AND maintain old tubers if you have to pay a tech to repair align the rig OR if you have to purchase the test equipment required to repair it yourself.

Better off getting a SS rig and enjoy making contacts.

 

[wavrider]

Audio/Final tube was mentioned

 

[Tallman]

They are fun to use, BUT unless you know how to maintain them and are WILLING to invest in the test equipment required to maintain them then my statement stands.

It is more expensive to operate AND maintain old tubers if you have to pay a tech to repair align the rig OR if you have to purchase the test equipment required to repair it yourself.

I have a complete repair shop and a faraday cage for calibration work. So for me it is just my preference.

 

[wavrider]

I have a complete repair shop and a faraday cage for calibration work. So for me it is just my preference.

Same here
SWAN 700 CX, Yaesu FT-102, Kenwood ts -820, Kenwood ts- 830.

My preference also, and I have the test equipment to keep those old rigs performing great.

The average hobbiest does not.

Kenwoods use 6146 not a sweep tube, neither is the FT-102 uses 3 of the 6146.

Swan uses the 8950 for a final, I have a box full of them for spares.

 

[Captain Kilowatt]

Audio/Final tube was mentioned

I took the wording "bad (audio/final) tube" to mean either type like a 12AX7 audio tube and a 3-500Z RF tube. Lots of, well most tubes, can be used for audio service if they are able to be used for RF service. 807, 811A, 572B, 833, 3-500Z etc can all be used for either service. The 6146 is what is known as a beam power tube and is actually in the same class as the 6L6 and 807.