Testing for tube shorts

Zero Cool · 31st May 2008, 07:17 PM

How does the "shorts" function of a tube tester work??

Lets say i have a bunch of triodes and no tube tester with a shorts function. How can i set up a testing system???

IE: when a tube shorts. is it generally a direct short that could be measured with a multi meter?? or is it a low impedance situation that shows up with the tube filament is lit and HV is applied??

Lets say i have a test set up where i have a tube in a socket with a filament transformer and a HV Dc supply. How would you test??

Geek · 31st May 2008, 08:09 PM

Hi,

Basically, it's a neon bulb in series with a capacitor, limiting resistor and the tube and AC is applied.

A good tube or tube section will have a diode effect, rectifying the AC to DC, which cannot pass through the capacitor, hence the bulb doesn't light.

A shorted tube or section won't have this diode effect and AC will pass, lighting the bulb.

Cheers!

Zero Cool · 31st May 2008, 08:22 PM

AHHHHH I see....Ok, Any suggestions on the size of the capacitor. I have one specific tube in mind to test that has a 250VDC plate rating. If just use 110v ac line voltage as the test with a neon and resistor rated for line voltage. what size cap should i use???

Geek · 31st May 2008, 08:48 PM

Hi,

Never use the line voltage. Isolate it.

Here's the schematic for my DC grid-shift tester. Take a look at the shorts indicator circuit:
http://geek.scorpiorising.ca/GeeK_Zo...24471#msg24471

Isolated 120V, 0.1uF cap with 6.8K resistor (between the 6.8K and 0.1uF, current is limited to the bulb OK) and NE2H. The 220K across the bulb bleeds the DC out of the cap.

Cheers!

31st May 2008, 07:17 PM	#1
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	Testing for tube shorts How does the "shorts" function of a tube tester work?? Lets say i have a bunch of triodes and no tube tester with a shorts function. How can i set up a testing system??? IE: when a tube shorts. is it generally a direct short that could be measured with a multi meter?? or is it a low impedance situation that shows up with the tube filament is lit and HV is applied?? Lets say i have a test set up where i have a tube in a socket with a filament transformer and a HV Dc supply. How would you test??

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31st May 2008, 08:09 PM	#2
Geek diyAudio Member Join Date: Sep 2004	Hi, Basically, it's a neon bulb in series with a capacitor, limiting resistor and the tube and AC is applied. A good tube or tube section will have a diode effect, rectifying the AC to DC, which cannot pass through the capacitor, hence the bulb doesn't light. A shorted tube or section won't have this diode effect and AC will pass, lighting the bulb. Cheers!

31st May 2008, 08:22 PM	#3
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	AHHHHH I see....Ok, Any suggestions on the size of the capacitor. I have one specific tube in mind to test that has a 250VDC plate rating. If just use 110v ac line voltage as the test with a neon and resistor rated for line voltage. what size cap should i use???

31st May 2008, 08:48 PM	#4
Geek diyAudio Member Join Date: Sep 2004	Hi, Never use the line voltage. Isolate it. Here's the schematic for my DC grid-shift tester. Take a look at the shorts indicator circuit: http://geek.scorpiorising.ca/GeeK_Zo...24471#msg24471 Isolated 120V, 0.1uF cap with 6.8K resistor (between the 6.8K and 0.1uF, current is limited to the bulb OK) and NE2H. The 220K across the bulb bleeds the DC out of the cap. Cheers!