Simple tests for Tubes with a Multi Meter

[@rogerc2714]

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.

[@FrenchieFilms]

+Roger C glad to hear!

[@edkennedy577]

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.

[@paulbrown6850]

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

[@jeraldjensen7425]

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.

[@shepardleroy6036]

instablaster

[@JonDeth]

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

[@shanesonn]

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

[@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!

[@FrenchieFilms]

Thanks, glad it was helpful

[@zabtej1645]

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.

[@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?

[@FrenchieFilms]

+Russell Catchpole I'm talking about the max before it fails, not the normal oppression point of 6.3 volts. The point was that well over 100 volts went through the heater line and cooked the filament

[@4142Wilb]

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.

[@FrenchieFilms]

Absolutely correct, this is just one way to tell if tubes have failed in a catastrophic way that you can check for shorts. There are even tubes that they will pass a tube tester, and still sound horrible

[@onesadtech]

Great video, thanks for this information.

[@FrenchieFilms]

You're very welcome

[@kevinpaul1719]

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 .

[@FrenchieFilms]

+Kevinpaul Moore gear to hear the tip was helpful :)

[@thomasharlos6872]

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.

[@FrenchieFilms]

You have to know the tube numbering and then you can search for them. I've found ever single one I've needed online.

[@thomasharlos6872]

@@FrenchieFilms Thank you so much. Unfortunately some of the tubes either do not have a number, which I find unlikely or, the number has been rubbed off, which is more probable. However I will keep trying. Have a great day and thanks again.

[@audiophileman7047]

@@thomasharlos6872 You probably figured this out by now, but if you didn't and for others who have this question, I would first look to see if the tube number is etched in the tube base. If not, find a schematic diagram for your radio. Then look to see what the radio manufacturer specified for tube numbers by socket. Those should be the tube numbers for the tubes that went in the corresponding slots. Otherwise, you'll have to find some used and/or buy new tubes with numbers.

[@mottosierra1372]

I recently bought a marshall sl5 but it doesn't sound anything like the ones I see on KZbin 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

[@FrenchieFilms]

That could be the tubes or it could be the multimeter. It can never hurt to have a spare set of tubes and swapping them out to test is easy. Tubes are still pretty expensive, but if they're old they can start to conduct poorly and make significant changes to tone for sure

[@mottosierra1372]

@@FrenchieFilms thank you

[@gilbertocruz1683]

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...

[@allanjohnpaligar4058]

Thank you so much, this video is so useful!

[@FrenchieFilms]

You're welcome

[@johnsimms3957]

Thank you for the tips.

[@FrenchieFilms]

+John Simms you're welcome :)

[@qua7771]

is there any way to match a pair of power tubes? Could I measure each mA value of them through a single ended amp using the same test tone?

[@FrenchieFilms]

You need to measure a lot of variables to match tubes. That works probably get you pretty close though yes. For guitar amps for sure. For hifi maybe not

[@jm101]

I found a 6u10 zenith tube with 12 pins the seal was good but I can't find the data sheet

[@FrenchieFilms]

Here's an article about the tube vinylsavor.blogspot.com/2011/12/tube-of-month-6u10.html?m=1 and in that article it also has a link to the datasheet. It's a GE datasheet, but it's going to have basically the same characteristics

[@buttonsdah5335]

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

[@Endfloat]

Thanks for making this video. Very helpful!

[@FrenchieFilms]

You're welcome !

[@emmaoliver8241]

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

[@mikelee1906]

Can you run 6.3 volts to pin 2 and 7 to just light the filament?

[@FrenchieFilms]

You definitely can, but that is less simple for most than just using a dmm. It also doesn't confirm if other pins are shorted that shouldn't be

[@mikelee1906]

@@FrenchieFilms Thanks for the reply. I was not asking the question in regards to testing. Your way seems perfect. I have received 50 tubes and was wanting to work them into a couple of projects. With microcontrollers and other electronics. I do not want to use high voltage.(I don't trust myself) I just want to light the filaments.I came across your video and you seemed to know tubes inside out. I would imagine polarity matters. Pin 2 positive. 7 ground. Probably will have to find data sheets on the ones I have. I was hoping their was any easy standard way to light any tube. But I am guessing that is not the case. I also assume tubes are not dangerous with only 6 or 12 volts to light the filament. Great videos by the way! I use to have many many tube amps when I played guitar in bands in LA in the eighties. Two of them caught fire during shows. Where were you 30 years ago? We could have used you :) Thanks.

[@FrenchieFilms]

Gotcha, I misunderstood. Heaters can run on AC or DC and polarity doesn't matter. it also depends on wiring as to how much current and voltage you need, and it depends on the tube type. You'd need to look at the datasheet. Many of the common power tubes (EL34, 6L6GC, 6V6) use pins 2/7 for heaters, and need 6.3V (DC or AC). They'll draw varying current per tube and you'd need to look that up in the datasheet. They always list heater current. For preamp tubes, the more common 12A*7 type (12AX7, 12AY7 Etc) they can either be wired for 12v operation, and use half the current or 6 v operation and double. pin 9 is the midpoint on the heaters, if wiring at 6v you jumper pins 4 and 5 and connect one side to 4/5 and the other to 9. If using the other method, don't use pin 9 and connect one side to 4, the other to 5 for 12v operation. Hope that clarifies. To know for sure what you're doing you'd need the exact datasheet of the tube you're planning on using. Each can vary pretty significantly in pinouts and heater configuration(s) and current draw.

[@mikelee1906]

@@FrenchieFilms Great info!! Thanks again!! I appreciate your time. I should be all set to begin to experiment with them. I have been collecting data sheets and studying them for a couple weeks. Also watching videos about how tubes work in general. So what you said makes sense to me.

[@neurot11]

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?

[@FrenchieFilms]

Not that I can think of. It can be dangerous to do more unless you understand how to work with the inside of a tube amplifier. Swapping tubes can help rule out bad tubes but that's about it.

[@CC-te5zf]

Just to summarize: You had a tube that had an internal short. Because the heater circuit is usually tied to all the tubes, the short shared the high voltage with all the tubes and caused multiple component failures? I'm fairly new to tube amps and with all the tube madness going on right now, I'm looking for a bargain in used tubes. But - I will definitely ignore some recent advice I got that basically said, just plug them in the amp and see how they sound. Yikes! I could do allot of damage that way! I've downloaded the spec sheets for my tubes and I will do this simple test for shorts with my trusty multimeter. Is there any other considerations? Is it worth to pay someone to test my tubes, for example if I needed a matched set? Thanks!

[@FrenchieFilms]

You have hit the nail on the head, but the test I did here can confirm if there is a short term any other pin to the heaters pretty quickly

[@CC-te5zf]

@@FrenchieFilms Thank you - this simple test is even more crucial given the tube shortage! Thanks!!!

[@animals.as.teachers9439]

How do you know how many pins should have continuity for each different tube? Thanks

[@FrenchieFilms]

The tube datasheet will tell you which pins are heaters and those are the only ones that should have continuity

[@jimbo1959]

Yesterday I Switched my Marshall DSL20CR watt switch from 20w to 10w while it was on, and not in stand-by mode ( was distracted ). I think I blew a tube,as I only get REALLY low volume now.Any idea to help me out Frenchie?

[@FrenchieFilms]

Sorry, not reading these comments as much as I used to. It's hard to guess from just the comment, you can definitely try swapping out the tubes, and if the problem persists, it may be something on the board and needs a tech to look at it.

[@jimbo1959]

Thank You!@@FrenchieFilms

[@tolerbearALTII]

I have a Precision Electronics S35 and I'd like to convert it to a 2 channel guitar amp. One channel for clean and one for a modern metal distortion with a huge sound. Is this possible without too many changes using the stock tubes? It has 2 6EU7s, a 6C4, and 2 7868 output tubes. Thanks.

[@FrenchieFilms]

If it already works as an audio amplifier, and already has two channels, then yes. It usually requires a few tweaks to the resistors and capacitors in circuit, but I'd suggest getting a schematic and sharing your plans on a forum. They're are many people on forums that may know that specific amp, and have made these types of changed before. Try Hoffman amps forums or ampgarage.com

[@aaronhartley6755]

Possible stupid question, if I connect two heater pins as shown on the data sheet and do not get continuity then is the tube bad?

[@FrenchieFilms]

It's very likely, yes, the heaters need continuity to work. What specific tube are you talking about? (You'd likely put the tube in and get 0 glow, but sometimes tubes barely glow and still work, so that's not a perfect test) Example a 12AX7 has heaters between 4 and 9 5 and 9 or just plain between 4 and 5, if you test between any of those three, you should get continuity beep.

[@aaronhartley6755]

All the 12 model tubes tested great. I had issue with two other tubes: 1) 50LgGT Output and 2) 35XZ5GT Rectifier. Here is the interesting part, if you look up the data sheet on the rectifier tube, the heater pins are 2 -> 7 but also 3 connects to 7. If I test 2-7 there is no continuity beep BUT if I connect 3 and 7 it beeps, ha. Does that mean it's actually working fine? This model needs all caps replaced so I have no idea if the tubes are the issue (no sound yet when plugged in) but I thought I would test the tubes while waiting for the cap replacements to arrive. Any thoughts?

[@dnantis]

Great video ! Someone game for free 2 GT 6L6GC tubes and one of them they said it was bad ! Well i measure them and one of them "beep" between pins 2 and 3 (filament and plate) and the other does not "beep"... So my guess is that pins 2 and 3 should be open and that tells me that this tube is shorted ??

[@FrenchieFilms]

That is very possible yes. I wouldn't put it into an amp unless you can get it on a tube tester

[@kevinpaul1719]

Thank you!

[@FrenchieFilms]

+Kevinpaul Moore you're quite welcome :)

[@riccardoz2953]

Hi there any suggestion to test AMPERITE vacuum tube? im triing to fix a GRC radio set. and i have issue on power box

[@FrenchieFilms]

The brand is less important than the type. I'd need more information to help

[@84leafclover]

I have a presonus tubepre, when i connect a condenser mic (MXL 990) the signal is really high even when the gain and drive knob are all the way down, is that a sign of a bad tube? Thanks

[@FrenchieFilms]

Not likely, tubes tend to get weaker and then just quit silently or start making odd noises. I don't know much about that schematic, but if the output is too high, one of the components in the chain designed to keep the tube biased may have gone out and the tube it running hotter. This will shorten the tube life and could have other consequences. You could still try swapping tubes to see what happens, but you might want to have someone take a look at the preamp

[@84leafclover]

Frenchie Films thanks

[@riccardoz2953]

verify if that mic values falls within presonus tubepre range of working, . verifiy also the cable, the phantom power and if that mic has a high signal even connected to a mixer witohut the tubepre of presonus

[@riverraisin1]

On a Tung-Sol 6FD7 I have continuity on heater pins 4&5 but also have continuity on pins 2&3 which both go to grid 2. Is that normal? Seems like if they're both going to the same grid it would have continuity.

[@FrenchieFilms]

+riverraisin1 you're correct, pins two and three on that tube are to the same grid, so you should also get continuity

[@silasfatchett5693]

The EL34 cathode and suppressor grid are not connected internally. If a pentode's cathode is connected, it will be connected to grid 3, the suppressor grid.

[@FrenchieFilms]

+Silas Fatchett thanks, I did the video about a year ago, so I don't recall all the details, but I do recall the most important points. 1. Only heaters should have continuity, 2. Check your datasheet got the pinout of the tube you're working in to be sure if for some reason this is in error. The major fault I ran into was the anode was shorted to the heaters, and roasted the entire amps tube heaters

[@qddk9545]

I am planning to do a little 9-pin preamp tube tester with a fixed freq oscillator, 2 sockets, one for 12AX types and one for 6922 types with the tubes wired for 6.3v. Configured as common cathode amp stages. If I put say 100 mV in, I would be able easily to calculate the amplification pr. stage. BUT ... how do I determine if the tube still is very good, good, fair, not good. Does it loose amplification when it gets worn out?

[@FrenchieFilms]

I don't know the exact answer. I think there are rated response curves with input voltage and the like and it should amplify current and voltage by expected ratios as defined in the datasheet. This is a bad explanation, but the best I can think of to try. There's a thread about this and the design by R.G. Keen of geofex.com on the Ampgarage forums you should look for.

[@qddk9545]

@@FrenchieFilms Than you :-)

[@Blaydrnnnr]

Cool vid.... I'm just starting to try to work on my vintage amps and this was a good quick test for tubes. I have a Marshall at the moment that is microphonic ( by tap test ) in the first preamp.. but when I change the tubes out, its still noisey when tapped. Maybe a bad socket??? I'm going to go through my stock of tubes with this test just to check them out and get used to my meter better...thanks...

[@FrenchieFilms]

+Blaydrnnnr yup it's a quick way to find duds, so you can put them in the bin

[@driventone]

V1 most Marshalls is very high gain. Almost all tubes amplify at least some sound when tapped. In my 2204, I thought a good tube was microphonic because I heard the tube shield rubbing against it, through the speaker, when I put the shield back on. You will hear sound of you tap the tube on that amp. If it’s microphonic and truly bad, the sound will be very very loud when tapped, and probably also ring.

[@andrewdg90]

Hi, do you know what pins should and what pins shouldn't have continuity on 7027A tubes? Thanks

[@FrenchieFilms]

Pins 1 and 4 (grid 2), 5 and 6 (grid 1), 2 and 7(heaters) everything else no connectivity

[@andrewdg90]

@@FrenchieFilms thanks a bunch! I might need to ask about 2 more types (on an organ amp). Anyway, for now have a Happy New Year!!! Thanks again

[@FrenchieFilms]

Same to you!

[@Dodzee.44]

i wish i knew someone like you,i have a couple of amp need testing

[@FrenchieFilms]

Sorry, I would love to, but unless you're close to the Seattle WA area, that would be hard :)

[@Dodzee.44]

can i hear if my tubes are faulty by tapping the tube with a screwdriver gently of course

[@FrenchieFilms]

+Gregory Dorrell yes you can, but something a bit less hard, like a pencil or chop stick is better, tapping a bad tube tends to make all kinds of noises. The first preamp tube can sometimes make very small noises this way and isn't a sign of 'bad' things because it is the most sensitive in the amp, but if it makes really obvious noises it may be bad too. It can't hurt to try and swap it with a new tube to see how it sounds.

[@BCTGuitarPlayer]

Gregory Dorrell buy a multi-meter and give it a shot, or check out the blogs and enter your questions thru your amps manufacturers websites. If it worked for me...you might get lucky too. Not to mention saving lots of money and learning a ton at the same time;)

[@w9x7cv3vg6]

is this the only way a tube can go bad ? with shorts on all pins besides the filament !

[@FrenchieFilms]

No they can just start getting weaker over time and start sounding bad, or start cutting out. They can become microphonic as well and start picking up noise that way too

[@TheStringbox]

Thank you, sir!

[@FrenchieFilms]

You're welcome!

[@SaveAmerica-TRUMP2024]

I need to test tubes for an old radio, but I have no idea what pins should have continuity and what pins should not. I need a vintage radio repair guy who has a tube tester to test my tubes. I was just going to buy a tube tester on ebay. I quickly realized either the tester is some crazy amount like $200-300, or the seller is listing as non-tested/ as is. Since I only spent $35 on the radio its not worth buying a super expensive tester, it would actually be cheaper to just replace every tube with new ones at $7-10 each. An un tested, who knows if it works ebay tube tester is worthless to me. I wish it was 1962 again and I could just go to a local grocery store and simply test my tubes...

[@FrenchieFilms]

Yeah, not fun. The old radio's likely also need other work, like electrolytic capacitor replacement etc. If you are anywhere near the Pacific Northwest I could help :)

[@georgegrat]

youre the best, thxs

[@FrenchieFilms]

Very welcome!

[@CRYSP45]

I got 3 boxes of vacuum tubes my fiance sort of inherited from his father after he passed looking on eBay some of these are worth a lot of money got a few Emitron Kt66's for example... but it's 3 boxes of all kinds of things mixed together some I'm not sure if they work or not... .. you don't happen to be in SC do ya. lol

[@FrenchieFilms]

+crayzee Crystal sorry nope, I'm up in the Pacific Northwest.

[@CRYSP45]

Frenchie Films lol I got 3 boxes full of these tubes and I don't know anything about them other than I see some of them.going for a pretty penny on ebay

[@FrenchieFilms]

Yes but to sell them for those prices, you'd need to get them tested to confirm they're good, or know they're new in the box (NOS New Old Stock). You may be able to find someone willing to test and sell them for you and take a part of the profit, or buy them bulk from you. Send me a message, I could take a look at some photo's to tell you some pointers etc.

[@BCTGuitarPlayer]

Can most guitar amp tubes be tested the way you showed us with the 12AX7B? It worked great! I just tried it on my questionable 12AX7B, so thanks for that!

[@FrenchieFilms]

Most 12a(letterhere)7 that I know of are identical pinouts. You can always pull up tubes data sheet to confirm which pins are the heaters

[@nsc217]

This doesn’t show that the tubes have full power?

[@FrenchieFilms]

this doesn't test emissions or any other functionality of the tube other than the heaters should have continuity, and no other pins should... Some tubes have shorts and are clearly defective, this can be proven easily with this method.

[@whynotme5926]

good info,thanks.

[@FrenchieFilms]

+why not me you're welcome!

[@orlairyissa1148]

thanks frenchie

[@FrenchieFilms]

+orlairy issa you're very welcome :)

[@MichaelBorne-rh8co]

Which two pins on a 6L6 tube? Out of peavey encore 65 amp. When powered on it hums loud. And with no instrument cable plugged in or not. Nothing plugged in, power it on, after about 20 secs loud hummmmmmm. Constant. Knobs dont change anything. So, I still wanted to check the two 6L6's, just not sure which pins to use, they have 6 pins. There's 2 of these tubes. I checked all four of the pre amp tubes. Showing 150 continuity on each. Assume they're good. You know which pins to check on 6L6's? And theres no numbers on these type as well. Thanks!!

[@FrenchieFilms]

6L6 heaters are on pins 2 and 7 so you should only get continuity on those two. Nothing else.

[@huriyazubairy342]

kitna kharcha ata hai tube test mai

[@FrenchieFilms]

+huriya zubairy sorry I didn't understand

[@landoe8383]

Cool

[@reyznbran9586]

Frenchie Films are you french ? good tips by the way, thank you

[@FrenchieFilms]

I'm not french, but speak fluent french, and have french bulldogs :) Thanks for the feedback!

[@reyznbran9586]

Frenchie Films si c`est celui sur la photo il est mignon, lache pas la video, au revoir !

[@FrenchieFilms]

Oui, c'est Maximilien mon petit Bouledogue Francais ;) I'l est drôle, mais un peu bête :) Merci bien!

[@kevinpaul1719]

I speak French I have an apartment in Paris. The terrorists Shit I have not been there in a couple years.

[@doncalloway9745]

You talked too fast. Cannot understand what # pins to check on the 12ax7 for continuity ! Not much help.

[@FrenchieFilms]

Sorry I can't undo that, and I only get told I talk too fast constantly. I've tried, but fail to slow down... it's just how I am. On the other hand, youtube does have a feature to slow down the video and thereby the audio. Give it a try.

[@arkhilious]

I'm a bit late, but you could look for the datasheet online.

[@nor4277]

I wish more company's still made tubes I think someday they will be hard to find .

[@Cam_B]

there's plenty of companies out there (JJ, EHX, mullard, sovtek) the list goes on...

[@SaveAmerica-TRUMP2024]

Well either all 5 of my radio tubes are bad, or this method of testing is useless...

[@FrenchieFilms]

What tubes are your radio tubes?

[@jeridwalters9204]

It probably depends on the type of tube. Keep in mind, he only tested one particular model of tube. Probably best to get a diagram / schematic that tells you which pins should have continuity...

[@riccardoz2953]

@@FrenchieFilms he has the model TROLL . nice video i liked how u easily explained it.

[@SilverMoonJoe]

Thanks for the video! Very Instructive!! 73, joe-k4jga

[@FrenchieFilms]

+Josef Ayala thanks, appreciate it!

[@FrenchieFilms]

+Josef Ayala thanks, appreciate it!

[@valvoxvo2755]

YOU DON'T KNOW WHAT YOU'RE DOING

[@FrenchieFilms]

Interesting point of view, could you help clarify what specifically I don't know? I'd love to learn more.

[@ehtcom]

You really need to test for shorts with the tube hot and a high voltage applied. Using a low voltage ohm meter will not give a reliable indication of shorts.

[@kevinpaul1719]

I used this test and all the tubes from my amp that blew up failed. I tested the new tubes and they were good. I very good easy test that I will use all the time. Very helpful. You did a good thing today.

[@RussellCatchpole]

@ehtcom Yes but then you can kill the PT while you are performing the test right? The point of this video is a very simple test for a shorted tube without a tube tester and no risk to the other components.

[@kevinpaul1719]

Russell Catchpole how? The amp is no where in sight?

[@valvoxvo2755]

that's not the way to test tubes,LEARN MORE

[@FrenchieFilms]

That's a very productive response, I'll definitely LEARN MORE!