Simple tests for Tubes with a Multi Meter

How to test your tubes with a multimeter. A simple way to ensure there are no shorts or bad heaters in your tubes.

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Please watch: "Marshall Dual Video 8"
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[rogerc]

Thank you so much for this video. My bass amp blew a fuse a few hours ago and this method weeded out the bad tube quickly.

[paulbrown]

I have just purchased some old valve radios and I needed to check the valves to see if they are OK, now I can check them without getting hold of an expensive valve tester. I have the old wax capacitors to change plus the mains leads and check the wiring as being old but this video is very helpful, many thanks from across the pond
Yours Faithfully Paul

[edkennedy]

My marshall DSL20 took a low fall out the back of a mini van when I was on my way to practice. My amp only put out low sound when I cranked it to ten. I found a bad preamp tube because of you're vid. Great vid, thanks a lot.

[shanesonn]

Thank you so much. I'm restoring a Crosley Model 9-201!

[jeraldjensen]

Thank you for the video I wanted to add that when I tested the heaters on a 12ax7a tube I found that when I tipped the tube vertical to horizonal I lost one of the heaters. Thus you may want to rotate the tubes as you test.

[JonDeth]

Measuring resistances as well as capacitance between grids to plate and cathode will surely be useful as well.

[jettramel]

My old Sivlertone amp just died, needed this video to test my tubes, great start before I take it to the only person around that can work on them. Nice video!

[Wilb]

Yeah, I tried this said method in detecting faulty power tubes. I even used the tap glass with a chop stick and visual inspection but nothing to indicate a faulty power tube(s). I had a whooshing sound emanating from my amp guitar plugged in or not, replaced all preamp tubes - same result. I replaced all power tubes, biased and turned in amp - no whooshing noise thus far. I’m convinced there is really no sure way in detecting a bad tube unless all avenues have been explored - timely & costly at times.

[zabtej]

Instead of the continuity check I like to run low Ohm resistance meter, because it can be helpful with low resistors where the continuity would just kick in. It was particularly useful before the transformer winding ratio measurement and also with the negative feedback causing some ground measurement problems early on when I learned the circuitry.

[gilbertocruz]

Thanks for those tips man...I have three identical Ruby 12ax7 and two of them have continuity on pins 9, 4 and 5...just one of them have continuity only on pins 9 and 5...maybe this one is bad?...when plugged on the amp the power tubes will light up but none of the three 12ax7 will...and the amp has no sound...

[kevinpaul]

I have a bias meter, but to find a the bad ones in my stock this test picked them out. The three bad ones that I found doing it this way were definitely bad. Fast just to tell me the trash from the good tubes. Not how good I will know one day won't I .

[onesadtech]

Great video, thanks for this information.

[emmaoliver]

Perfect, thanks, exactly what I needed to know to test my Brimar ECC83

[allanjohnpaligar]

Thank you so much, this video is so useful!

[Endfloat]

Thanks for making this video. Very helpful!

[neurot]

Hi and thanks for the great video! I have a 1963 princeton amp(was completely serviced 10 or more years ago and prolly played around 6 times until 2018) I brought it out today and the sound is distorted. I tapped the tubes- nothing, i cleaned sockets and resat tubes-nothing, i just multimetered per your video, continuity is good. Is there anything else I can test before taking it to a tech?

[thomasharlos]

Hello, nice video by the way. My question is where do you get these data sheets for the bulbs? Is this something I would have to look up on the web as I am pretty sure some of my bulbs have this writing worn off. It is from an old 1950s' Marconi radio. Any help would be appreciated. Thanks again and have a great day.

[RussellCatchpole]

Really helpful thanks. Just one thing; at 3:43 you say the max voltage for the heater should be 100 - 200v. Shouldn't it be around 6v for the heater and 200v for the plate?

[mottosierra]

I recently bought a marshall sl5 but it doesn't sound anything like the ones I see on YouTube I feel like it doesn't have bite or full of gain like the ones I hear here, I did the tube test as you show and they all have continuity but the numbers on the screen from the multimeter they go crazy going up and down, I think they are the original tubes that came with the amp, do you think I should still change them and see if there is any improvement? thank you

[buttonsdah]

i have two 12SG7 tubes, the heater pins are 2 & 7, they both test fine, however pins 3 (marked cathode & grid number 3) & 5 (cathode) test positive for continuity. I'm not sure if that's supposed to be that way or not, how do I tell if these are bad tubes? I'm looking at the diagram but don't know what to look for