testing rectifiers in tube testers

[Scott Johnson]

My $.02-
The one type of tube you can surely test on even an emission only tester is
a rectifier, but it will only confirm a bad tube. You may have a gassy tube
that will not test gassy because of the relatively low applied voltage (not
enough to ionize the gas in the tube) this holds truer for rectifiers
because the higher plate voltages they encounter. Also, with 5U4 type tube,
if the oxide material is flaking off the filament, chuck the tube!  This is
an indication that the tube has had a shorted load, or has many thousands of
hours.  I check voltage drop per the data sheets on a home made jig with the
stated load current, this is probably the most conclusive test.

73,
Scott KC7BGE

-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTSERV.TEMPE.GOV]On Behalf Of WSHU ENGINEERING
Sent: Tuesday, January 15, 2002 8:36 AM
To: BOATANCHORS at LISTSERV.TEMPE.GOV
Subject: Re: testing rectifiers in tube testers


----- Original Message -----
From: john w. king <jbkking at BELLSOUTH.NET>
To: <BOATANCHORS at LISTSERV.TEMPE.GOV>
Sent: Monday, January 14, 2002 3:14 PM
Subject: testing rectifiers in tube testers


> I have several 5U4GB rectifiers that I have tested on my B&K mutual
> conductance tube tester. All of the tubes check weak or QUESTIONABLE  on
the
> tester. Are tube testers relatively accurate indicators of the quality of
a
> rectifier tube such as the 5U4$GB . Whaty has been your experience? 73,
> John, K5PGW
>
John,

Most tube testers have a diodes OK line which is usually in the "BAD"
portion of the meter, if it reads above that line, then the tube is supposed
to be good. I agree with the philosophy that the only true test of a
rectifier is in circuit. put a volt meter on the B+ of a power supply under
load and compare the results of the tube(s) in question against a know good
or a new tube. You will usually see fairly radical differences on a bad
tube. The warm up characteristics are also an indication of how much life is
left in the tube. If a good tube brings the B+ up to snuff in under 30
seconds but another tube reaches the same voltage but only after 2 or 3
minutes of operation,  the slow tube is nearing the end of it's life even
though it still works.

73
Paul A. Litwinovich
Chief Engineer/ Webmaster
WSHU AM&FM, WSUF-FM
N1MUC
"RF IS GOOD FOR YOU"

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