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Author Topic: test equipment: tube tester  (Read 9549 times)
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David, K3TUE
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« on: August 21, 2005, 10:07:03 PM »

I was looking on ebay at available tube testers.  It appears that Hickok's command a fair price, especially the Hichok 600.  Are they worth it?
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David, K3TUE
w3jn
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« Reply #1 on: August 22, 2005, 07:42:38 AM »

You are to be commended for thinking about assembling the test equipment needed to support your station.  I'd put tube testers somewhere down on the list of necessary equipment, though.  The reason for this is you really can't trust them to give you a valid answer as to whether a tube is bad or not, and further, they will NOT tell you if the trouble you're having is the result of a tube or something else.

Many tubes that read "dead" on a tube tester will still function fine in many circuits.  OTOH while re-doing a National FRR-59A (a massive beast with 60+ tubes) I replaced a busted 6C4 with a brand new Raytheon.  The circuit still didn't work.  The tube tested as new in my Hickok, and I then wasted all kinds of time troubleshooting the rest of the circuit.  I could find no problems, and subbed a used 6C4 and it worked fine.  The new 6C4 wouldn't oscillate in that circuit yet the tester (which simply tests either emmission or, in the case of Hickoks, ability to amplify a 60 hz signal) found the tube fine.

A Hickok, as I stated above, tests the tube's ability to amplify a 60 HZ signal as well as some gas/leakage tests.  Makes it somewhat easier to weed out suspect tubes.  Other cheapo tube testers tie all the elements except the cathode to the plate and test it as a diode, in essence only tsting emission (some test leakage and gas as well).

You can do the same with a VOM.  Pull the tube and test resistances between all pins.  If anything is <1 Megohm throw it.  If any element to the control grid is <10 Mohm, throw it.  Check the filament resistance to make sure it isn't completely burned out.  Then, insert the tube back in the radio and read the voltage across the plate dropping resistor and screen dropping resistors.  Compare with the standard values for the plate voltage as found in a tube data book.  If the current is way low then it isn't drawing enough current and oughta be tossed (or you have too much negative bias in the grid circuit).  If it'ds drawing too much current it could be gassy, or you could have a bad coupling cap.  Check the grid voltage - should NEVER be positive.  If it is, the tube is either gassy or there's a bad couipling capacitor.

Yes this takes more time than just slapping the toob in a tester, but it also is more exacting and tells you much more about what's going on in the circuit than a tube tester ever will.

73 John
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« Reply #2 on: August 22, 2005, 08:30:00 AM »

John 6C4 is an odd beast also the 6U8 some just won't work as oscillators.
The tube was most likely good but from the wrong side of the tracks.   fc
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David, K3TUE
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« Reply #3 on: August 22, 2005, 02:45:51 PM »

You are to be commended for thinking about assembling the test equipment needed to support your station.

I am trying to be smart about where I will spend my money.  Thanks for taking the time to save me the money and the space.

[...]
Yes this takes more time than just slapping the toob in a tester, but it also is more exacting and tells you much more about what's going on in the circuit than a tube tester ever will.

So then would it stand to reason that a tube manual is more useful purchase?
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David, K3TUE
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« Reply #4 on: August 22, 2005, 03:35:11 PM »

You definitely need a tube manual, or at least know where to find the tube data on the internet.

Whether you need a tester or not I cannot answer.  Depends on how much stuff you're thinking of accumulating (remember, it starts innocently enough....) and fixing.  I restore lots of receivers of all vintages.  Were I to rate how much I use my test equipment I'd say the ranking would be:

1)  DVOM
2)  Scope
3)  Signal generator
4)  Freq counter
5)  Bench power supply
6)  Digital R/L/C bridge
7)  Tube tester
Cool  Spectrum analyzer

73 John
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Jim, W5JO
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« Reply #5 on: August 22, 2005, 04:06:16 PM »

I would also look for a Vacuum Tube Voltmeter to have the analog readout.  Most old boatanchors manuals state that you can put a VTVM  across the headphone jack to align the receiver.  A digital VOM is nice, but hard to use for this purpose, beside that you really don't need that accuracy.  I use my DVOM to calibrate my regular VTVM.
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w3jn
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« Reply #6 on: August 23, 2005, 08:28:14 AM »

Agree 100%, Jim, I mentioned that in the threat on VTVMs vs DVOMs.  My Fluke 87 has a bar graph display that does OK as an analog indicator for peaking circuits.  Also a DVOM is often confused in the presence of a strong RF field, which most VTVMs seem to be impervious to.

73 John
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David, K3TUE
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« Reply #7 on: August 24, 2005, 01:13:55 PM »

[...]
Were I to rate how much I use my test equipment I'd say the ranking would be:
[...]
3)  Signal generator
[...]

Would that be an AF or RF signal generator (or both)?
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David, K3TUE
David, K3TUE
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« Reply #8 on: August 24, 2005, 01:24:44 PM »

1)  DVOM

I have secured the an RCA WV-98C, which I hope will serve me well.

Quote
2)  Scope

And I am moving on to the scope next.  I have my eyes on a Tektronix 2235 as a compromise between cost, specs, and size.  Sadly, like filters in old receivers, you seem to have to scrounge for 'scope probes later with most sales I see.
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David, K3TUE
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« Reply #9 on: August 24, 2005, 02:09:58 PM »

An *analog* scope is much better for looking at AM waveforms, etc., than a digital scope.  I don't remember if the 2235 is analog or digital.  The 2200/2400 series are great - lightweight, good triggers, sharp traces.  Weak sppot is the power supply, but still they can go years and years with no problems.

It's good to have both an audio AND RF generator.  You can get by with an old audio sig gen (don't pay more than $20 for one), or a fuction generator that does sine/square/sawtooth.  For RF use I'd spend a bit more and get a HP8640 - look for one that has the freq counter input option - or a synthesized generator.  Again it depends on how much you're gonna use it.  You might be able to get by with an old HP608 tube-type sig gen, about $10, and use an external counter.

Best to start small and upgrade your test equipment as you find it cheaply.  If you find you're not using it you haven't tied up much money in it that way.


73 John
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Jim, W5JO
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« Reply #10 on: August 24, 2005, 03:28:12 PM »

I found a RCA WA 504 audio generator.  Although it is not tube type it produces nice sine/square waves.  They are cheap too.   Frequency counters can be found very cheap almost anywhere.  For example the MFJ 259B analyzer has a frequency counter mode.  If you haven't considered a 259B you might do so if for nothing more than antennas.  The 259 is also useful for determining the reasonance frequency of tuned circuits.

As for the RF gen., if you plan on working on equipment with low IF frequencies, then look for a URM 25 D or F.  They go low enough to align 80 Kc. IF stages.  They have two outputs, one that is attenuated and a high level you can feed to your frequency counter for accuracy.  Another option is a Sweep Generator that will tune those low IF frequencies.  There was an article in Electric Radio in Feb. 2004 on building one.  It uses inexpensive parts and can do the IFs if you don't find an RG Fen. that goes that low.
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Jim, W5JO
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« Reply #11 on: August 24, 2005, 03:31:06 PM »

I forgot to mention, look for a TEK 465M.,  100 Mcy scope and some 465s have a  digital voltmeter.  They aren't very cheap but it is good to have the bandwidth.
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