Eurotubes "Pro One" Bias Probe Evaluation.......Plus: Make Your Own Bias Probe 

Ala Carte MENU: Plate Current vs Cathode Current @ 01:50 Proper SE Bias Procedure Discussion @ 04:35 Performance of Manual SE Bias Procedure @ 07:16 Performance of Eurotubes SE Bias Procedure @ 12:51 Comparison of Results for SE Amp Circuit @ 14:05 Manual Measurement of Screen Current @ 15:08 Open 1st Gift Box w/Jack & KC @ 16:39 Performance of Manual DE Bias Procedure @ 19:31 Performance of Eurotubes DE Bias Procedure @ 25:33 Comparison of Results for DE Amp Circuit @ 26:46 Open 3 more Gift Boxes @ 27:38 Final Discussion of Eurotubes Bias Probe @ 29:36 Build Your Own Bias Probe @ 32:08 Closing Statements @ 45:58 Car Show @ 47:27

Always a good day when there is a new Uncle Doug video.

Uncle Doug, that was a masterfully done educational video. We love your amp videos and you have such a unique eloquent way of teaching us all!!! Bless you and your family.

Great video! I had an electronics instructor years ago that had been working on electronics for many decades. Some sage advice from him: “if you accidentally or intentionally touch the input of a rectifier while the circuit has power, it instantly becomes a Rectum-Frier”.

Thanks Uncle Doug, you're the best!

Thanks Uncle Doug, good review of measuring for tube biasing. Cheers,

A friend of mine used to own an amp repair business but closed a few years ago. He gave me a pair of these testers and they sure make biasing much easier. Thank you, Doug for teaching us that which cannot be found in any classroom today! I hope you are doing well, Good Sir!

The only suggestion I would make regarding making your own bias probe, is to chassis mount the tube socket, since output tubes can generate a lot of heat and wouldn't want to melt or singe the surface it rests on, and use recessed, isolated probe lead connections in same chassis to prevent inadvertent death sentence execution. As always, top notch teaching of tube theory, testing and appreciate you inviting us to your home, love of classic cars and pets. Miss Rusty.

Welll done video of the manual bias and the Eurotube Bias Probe.

Marvelous Doug! Really a great vid as usual, thnx !

Awesome build! Love the cars too! I see myself making an amp probe soon. Thank you for all the great ideas.

I learn so much from all of your videos. Plus we get gut shots of some real gems. Thanks Uncle Doug.

Thanks Doug for a new project to build and assist in my amp restorations.

THANK YOU for your generosity, David! More learning ahead. Uncle Doug - This vid was SO informative!

I think I will make one of those. Thanks for the gear donners and to you for making it possible.

THANK YOU David Freseto! (I hope I spelled that correctly). That was a very generous donation and I look forward for Uncle Doug to showcase your gifts. I can't wait for that Gibson Echo unit. Thank you Uncle Doug for another great video.

Thank you so much for this tutorial! I am a novice amp tech and was able to use your manual method to check the bias on my own '78 Hiwatt. Seeing you walk through the entire process step-by-step was extremely helpful.

That’s a lovely gift from David. I have to say all my vintage radio friends have always been generous.

You've quite the talent for sharing *great detail* very clearly, Uncle Doug. Plus, there's cats, too.

Uncle Doug, a most fantastic specimen of human being. Thanks for your work and for showing it.

I bought one of these eurotubes bias probe devices some time ago and I really like it. I knew I was a bit too ignorant to attempt getting the readings manually, so doing my best to avoid the Dunning Kruger effect and potentially kill myself I spent the money on it and do not regret it. super happy to know that it's proven accurate by one of my favorite uncles! Thank you for sharing your knowledge.

Great video Doug. A video that certainly needed to be done.

Thank you for sharing this information to help us with this hobby

always look at your videos you give a teaching lesson like no other and i thank you for being a part of my educational on electroniics

Fantastic instruction! The Eurotube tester is certainly convenient but I appreciate your snippet of the DIY method, as well!

Always awesome learning experience with your videos, thanks for sharing!

Very cool! Thanks for the demonstration.

Another great video! When I build mine I think I'll install the tube socket in the junction box.

Love the video. Very clear and detailed amp tech info , unbelievably awsome viewer contributions, and sweet hot rods . Don't think it could get any better than that. Oh yeah, and the cat's. My 6 year old son likes to see Jack because he looks just like his black cat named Herman. Thanks for sharing your knowledge and adventures Uncle Doug.

Thanks UD! I learn something every time I see the videos you post. That was some mail call. Thanks David. Thank Jim

David, thank you! Your generous gift will bring hundreds (?thousands) of viewers more UD videos!

Another great video Uncle Doug! Glad the probe is accurate

Nice video and lesson Doug, thanks!!

Great educational video, thanks Uncle Doug!

The best channel in the whole internet! Thanks Uncle Doug!

First I must say thank you, David and Jim!! Any fodder for future videos is awesome!! Next, I have to say these educational vids are my favourites!! Thanks so much for sharing your knowledge with us! Oh and say hi to Jack and the rest of the kitty clan for me!!

THANKS UNCLE DOUG hope u have a great day. I saw the cobra then POOF aww man my fav !!!! blue 427 side oilier and white stripes!!! GIMME GIMME GIMME ;-)

Another great video. I’ve done lots of business with Eurotubes since they’re local to me. I shared this video with them. Hope you and the cats will be celebrating Cinco de Meow this weekend.

Very good, Doug.

Yet another awesome contribution, sir! Thanks!

The most informative video about biasing. Thank you very much!

Excellent, Thanks for the video Uncle Doug & Warm Greetings from the Sunshine Coast, Australia

A most professional video. Wonderful generous patrons. That Gibson amp "David" sent is fabulous, not to mention the other items. I've purchased stuff from "Bob" at Eurotubes years ago and always recieved excellent quality and friendly service. Again, thanks for sharing your passion and patience in your videos/tutorials. The car shows are great! Keep your eyes peeled for an old Buick Roadmaster sometime, they have some nifty options on them. I had a few classic cars stolen when I was a younger that I miss. I recently seen an identical one that had been modified from a post into a hardtop and that was a 1950 Plymouth coupe deluxe with visor. The modifications to the body that they did made me wish I still had mine, so I could do the mods too. Absolutely beautiful! Mine was parked by a little old farm lady in 1964 just before she passed over. It had a imitation wood grain dash with a real cool large round clock with a ship on it too. It was stored there and during the Iraq war, metal prices went up and someone snatched it off the property before I could move it. So, who knows what happened to it? I reported it stolen, but the rural county law and state law weren't in the least bit interested in investigating it for some odd reason? Ya win some ya lose some. I believe it had a flat head 6. Pretty nice old car. Thanks!

Wow! Great video Uncle Doug and thanks to David too. So generous. Amazing!

Very cool little gadget, and fairly easy to copy. Thank you for taking time to show it! The black '34 was impressive, the T-bucket does look odd. Just when you said "tasteful flames", I was thinking "orange kelp". :))

Thanks Doug for another excellent informative video.......................................Berni

Not saying your old because obviously you're young at heart BUT I wish my uncle was as coooool as you.. Thanks for all that information, a real legacy

Very nice DIY bias probe.

Uncle D- You really are so deserving. You give so much to the community in your depth (or shall I say "girth") of knowledge. I wish I had something to offer. God bless you, Brother... (Edit- You got to love those fighting men that came home from WW II and just jacked up a bunch of cars!! Started a culture..)

Great demonstration Uncle Doug, of how to use "and build if so desired" the bias probe.. Your gifts from viewers like Jim and others, are out of this world.. I'm expecting some grandmother to send you her Mary Kaye Strat she bought new! You'll have to finish the Corvette story in another video.. Be well, Tom

Sweet video! Love the time stamps as well

Uncle Doug, Based on your posts I am pretty sure you are older than me by a few years, but wow, when I watch your videos do I ever connect with your "vibe", and I am guessing that there are thousands of others out there who feel the same. Please keep doing what you do. It is very educational and very important.

Thanks UD!! Another beauty!!

Great video. I got one of these, after waiting for almost a year for these to be back in inventory at Eurotubes. I think it was worth it though, as it's not easy to find one that reads plate voltage. Only other one I found was a kit that plugged into an existing multi meter. Now it's been sitting for almost a year and I never yet had the need to bias anything. Soon I have a '71 Super Reverb arriving though and I'm going to want to check bias settings for the (new make) Telefunken 6L6GC's I have set aside. I believe for this amp it would require changing a bias resistor (it has a balance pot but not a bias, if I remember right). This video is a great reference on using this probe. This channel is a great reference library on tube amp function in general

Learn something new every time, Always good stuff

I thought this was a 55min video on tube biasing, watched 10mins then stopped. It stuck in my head though so a few days later I've watched the rest - Wow, what a tressure trove of random elements that together prove its not all maths and music theory, its a whole lifestyle - Please keep adding car meeting sections, hot rods is what kept me playing 30 years ago!

Another great video, as usual, thanks!

Thank you for another great video.....

Classic cars and tube amps. Sounds like a great TV channel.

Wow fantastic, i would love a tube tester but way out of my budget in the UK, what a great gift

My cat, Souixsie Queue, saw Jack and Casey on the screen, and had to get a closer look. THEN she saw her brand of treats. You've got a new 4 legged fan!!!

Thanks for another great video!

Excellent video!

Thanks for another great video.

Best instructional videos on you tube. Thank You

Hello from Canada, Toronto Ontario. Like Always your Videos are educational, Thank you for your efforts.

Druel,druel! Old amps old cars. Love the biasing tool! I loved the black Ford. It is very similar to the last one I helped build. More engine than car.

You never fail to amaze! The probe part components are available on several sites on the web. I think building your own probe, like building anything, you know exactly what is in it and, most important, how it works! Like you said, the Euro tester is nice and accurate, but you can build one for under $20. Go figure. If you build it yourself, you can fix it yourself. It's a no-brainer! The cars ARE wonderful! In the early 50s we moved from Mo. to Roswell, N.M.. My dad bought a late model Hudson Wasp. It was, in his words, the best damned car he ever owned and he had many. We moved back to Mo. a few years later to help my Grandfather and the Hudson got repossessed. My Dad never got over it! Oh well. I learned a valuable lesson about over extending yourself. Thank you so much for sharing! Can't wait for the videos on those amps you got in the mail! Love them kitties! Thanxz

i made one of these for $20 ... this was a cool video love the cars

Thanks Uncle Doug, this topic is (currently) out of my pay grade, but I remain teachable. :)

I really enjoyed this video. Right about the time I started thinking about what might be inside the Eurotube unit, you started talking about how to make one. Perfect timing! I had pretty much sketched out what you had but was trying to figure out how I could power the meters from the filament voltage so I would not have to use external meter(s) to make the measurements. I would need two fully isolated supplies to power the meters which could easily be done off the filament voltage if it was in the 6vac to 12vac range; but then I hit a dead end when I thought about the much higher filament voltage tubes such as the 50L6......

Thank you for another great vid UD. I'm Glad you were blown away by my donations, They are worth the price of shipping for these master classes in amp restoration. BigDave.

Today!!!! was the big day!!! first time power on the supro tremverb. perfect!!!! thanks verry much Uncle doug!!!!! used this bias method for the class a 6v6 and it came out on 12.6 watts, but the 6v6s by jj has a max of 14 watts so thats perfect. it will eat a 6v6 tube once a year, but the sound is just amazing!!! also checked temperatures of all components using a infrared temp. meter all seemed verry cool. thank again!!! greetings from holland!!!!

Great video thank you.

Pretty amazing the way The mind works once You gain knowledge On things good idea On making your own current probes for electron tube biasing.

great one Uncle Doug

Great! That's exactly what I was looking for, how to make my own tube bias probe

Thanks to all the gentlemen that generously gave to Uncle Doug, and thanks to you Uncle Doug for another great video.

I think I'm addicted to these vids. I better go speak to someone. Lol... no seriously excellent to the point technologist makes it look so easy. Luv the concluding segments.

Thanks Uncle! cheers from Colombia

Hey Unkie It's me again- (seems like I recall a Frank Zappa line that started that way???? Ahhhhh Yes I think the Central Scrutinizer) I guess I just have too much time on my hands sitting here in my boxers all day riding out these days of minimal social physical social contact waiting for the coast to be clear of that pesky little virus that is creating so much havoc here in 2020! Spending alot of time online binging on You Tube and working some DX on the ham radio. 15 meters has been opening up a bit too..... Might you be a ham too? Well what do I have to say today that is relevent? Ok, great videos and great karma. This one is no less than great with excellent info and excellence at describing and explaining the processes of measuring bias. I never could understand why someone would go to such great expense as to purchase a tailor made commercial bias measurement device when there is a multitude of ways to measure bias and dissapation for free with your multimeter. Or for that fact it is so simple easy to build your own break out setup as illustrated in your video. I have employed many different techniques. In most scenarios I would usually measure the voltage drop across a cathode resistor and take the plate reading and not worry too much about fudging for the grid. I figured that it would fudge my dissapation calculation just enough to ignore and yet offer a margin of safety above over dissapating my output tubes. I often used to have an ear and a habit for runnin' em hotter anyways... Oh the errrr of my evil ways! When I started doing alot of amps as a service to others instead of just my own , it became more convienent to build a plug in device where I wouldnt always have to remove a chassis. So I built my own break out. Mine a bit different than yours for sure but likely not as accurate because of grid error and maybe not quite as versatile. BUT..... Certainly much SAFER! I employed a 1ohm precision resistor inside of my "Probe" with no high voltage current traveling thru my leads or into my meter. I am scared of high voltages (would you believe I have a specialized tube with a 7000V plate at over 500mA,power supply??? YIKES double digit kW output!) Getting off subject I digress except to say that yeah I am very fearful of high voltage but thats healthy! Long story short, I dont like running flying leads to the tubes and I would also like to add that maybe you might want to re edit the video to include a warning that whatever a potential builder to this device does, is that they clearly make sure that the leads that they use can clearly support higher voltages and that they dont use some innappropriate low voltage signal wire that could potentially break down the dielectric properties of its insulation! I didnt want to be critical but it might be worth pointing out. Back to the commercial bias measurment devices..... I thought I wouldnt ever find value in buying one of these types of devices UNTIL I ended up buying the most expensive, easiest, laziest and probably the safest and accurate one of them all. (this is not a product plug as a matter of fact I think that the maker has since retired and its no longer available or rarely avail. I am not sure?) I have a device called the CompuBias. It is a breakout socket similiar to all the others and it reads the actual current and voltages all very safely at the actual socket with no dangerous currents thru the meter or the leads. It has a microprocessor with its own firmware program (probably a PIC of some sort) and it will read your voltage, current and power all on its own LCD screen. YES for those kids born into the calculator age and slide rule is foreign to them,,,,,, This device performs all the calculations for you and gives you the power being dissipated too. EASY PEASY STUPID SIMPLE but almost stupid expensive too! However, it is such a productivity time saver and I was able to justify it as a start up business expense.... Which also I must comment on your estimate of professional help costing to bias an amp! I KNOW I AM UNUSUALLY CHEAP AS FAR AS WHAT I CHARGE AND I DONT HAVE ANY SET PRICING ON MY SERVICE But DAMN $100 bucks to bias an amp! WOW! Maybe I need to research my marketplace better. I know that I am probably in a more competitive location where amp techs are likely a dime a dozen with all kinds of fly by night hacks that do more damage than good but I just cant look someone in the face charging a hundred bucks while I pull out my little black box and it is so simple! The guy that called with a twin the other day, I only quoted him 20 bucks to check bias on the new tubes he bought and installed. (I know that was lowball and the luthier that I partnered up with on the shop gave me a ration of grief, but I figure it is a good investment in yet more future business,,,, (like as if I need to advertise or get more clientele, I am comfortable with the amount projects that I have to do for others for the next few weeks ) Finally in closing, I also want to thank the genrousity of your viewers and all the goodies that seem to be sent your way! I enjoy watching as you unbox some of these treasures! Especially the thoughtfulness to include goodies to your co-stars . I never been a cat person and now we have three. My snowshoe being my favorite furry child...... Wow! NOS tubes and vintage valvco and other misc..... Glad to see that good karma goes around (as if karma really works like that) and comes around. (Its good karma when I wake up and nothing bad happens and I dont learn a lost lesson the hard way!) Nice guys dont finish last after all! PS: your videos remind me of and look suspiciously like those machine shop videos by "TUBALCAIN" Your undercover is safe with me! GO CHECK HIM OUT!

Hi Doug...When I first started building amps, my buddy gave me some home made bias probes for the tube sockets. At some point, they got put in a box and mis-placed. I just started using my meter (an old Simpson 260 my dad gave me). I got fed up looking for my probes, so I finally got some new ones from Eurotubes. I was tempted to get these with the meters, but I felt I would just use my digital meters and save the money (I have an old Radio Shack one and a Fluke 77IV). A few years ago I finally bought an 87V Fluke. Those in your video from Eurotubes look great....easy to use, current and voltage on each tube. Super easy. I keep fighting the urge to get them. Great vid!

Excellent installment, Doug! This will be the go-to reference for bias measurements on RU-vid. I know you've covered this stuff before, but a nice companion piece to this one might be about the decision process that goes into selecting a particular plate dissipation. Would be great to bring up some sine wave test tones on the 'scope and show how they're distorted by the output tubes in different ways under different biases as well.

Thank you so much! Very helpful.

thanks for sharing!! glad ppl are feeding your kitties too,.,.,🌿

Ótimo fim de semana para o Sr.obrigado por mostrar esquemas detalhado Sul do Brasil

I just love the cats. Jack must be a union guy on his off day! Uncle Doug, not only are you super helpful tube amp creator, you take care of all the stragglers and homeless bum cats lurking around your yard. Since the strays can’t talk, I’ll say *THANK YOU* for them!

Doug, you and I are in general agreement as car critics ;) Great video as always!

I have two of these. Very much worth the money

Excellent. I have a Compu Bias unit that is similar but has two leads so it will measure two tubes at the same time. Also gives a direct display of Plate Voltage, Plate Current, and Plate Dissipation. Makes bias adjustments a breeze. Pricey, but one of the biggest positives is that it improves safety by eliminating the need to insert your hands in the HV multiple times. If you Google it, you can see some excellent photos of it in action.

nice instructional video. had a watch last night and the old grey matter dragged up a memory from college regarding DVM accuracy i seem to remember we were told to pretty much ignore the last digit displayed so for 23.33 we would take it as 23.3 and 23.37 would be 23.4 as the meters were not precision instruments. there is probably more to it than that for sure and that was mid 1980's but as I said the grey matter thought about that and your results and thought they would be even closer between the two sets for manual and with that nice piece of kit if taking that view of the meters. but of course it all falls down with the one displaying 263V as there was no decimal to worry about. now to watch the end with the hotrods, what a great mix of viewing pleasure.

Another super video, Uncle Doug. The Eurotubes device looks like a great buy if one has to bias a lot of amps, as in a repair shop situation. For us who only own several tube amps, the traditional bias method will suffice very nicely.

41:34 That's too funny! Great job as always. Sweet cars too.

Great vid! I've been doing cathode bias measurement the wrong way! Love bias probes, though. I have a Weber Bias Rite I got from Eurotubes. My favorite tube supplier, BTW. Love it except that the "heads" are super fragile.

I use this guy. Love it. It’s great

I am so impressed by your accountability in learning Uncle Doug. You learned a new understanding of determining plate voltage, confessed to it, and made it the object of this lesson. Talk about metacognitive teaching and modelling! BTW, I am still trying to put together a linear list of your instructional/electronic theory videos, starting from "How a Tube Amp Works" in about 2014 (?). What I chase on this topic is scattered all over RU-vid. I have begun a document that lists topics by date of posting but I am so in need of a master list by anyone who has a list of Uncle Doug's "How it Works" videos that starts from the beginning and ends at the most recent. This is stellar learning/teaching and I know it has a logical progression that I can't easily determine. Enough of my beef. I am prepared to send some Bluegrass recordings to the first person who can furnish me with the chronological list of how the amp works from input to output with all the components in between. I warn you: these recordings are my wife's, she being 3x Grammy nominee Claire Lynch. I bet you'll enjoy listening to her music while soldering up and testing your next great build/repair.

42:27 - A lid from an aerosol can! Great new 'killer app' :)

Good video! I use my Eurotubes Pro One bias probe to bias my Marshall 2203X 100 watt master volume head. I believe using this probe will pay for itself after about two or three tube changes. Not only that but lifting and carrying this amp to a tech is quite a chore as it's really heavy. The bias probe is worth it in my opinion. I use the probe to keep my tubes out of the danger zone so to speak. I fine tune the bias by playing my amp with the probe installed. I found that I like the tubes to be biased at about 60% dissipation. This gives me more clarity in the bottom end. Which also gives me more crunch without a muddy tone. Another cool thing about the Pro One is it doesn't need batteries.

tube amps, cats, dogs, hot rods, education, if this was the only channel on RU-vid it would be worthwhile.

Gosh you're pleasant to listen too.