D-lab series Basic Training Tube Guitar amp repair Balance vrs variable bias system fact or fiction

You asked, I deliver. Going back to basics, focus on the real cause of the tube amp fault. This new series will address many common malfunctions, help you to quickly resolve the issue, no BS, instant solutions. I have shown many full repairs in the past, many questions have surfaced, now I will address them and give you to easy resolve. I am doing my best to guide you thru the process. I dont want to leave this world without leaving this legacy! Now, to up the game, I am introducing a new MC "Fred Caddy". He and his sidekick Fink will contain the subject matter for each video. This time we will focus on Fender type bias systems. Bias is very important for the longevity of your output tubes plus the sound quality of your amp. I always recommend to my customers reconfigure to variable bias, install a nice matched pair of tubes. The decision is yours. Hey guys, D-lab is full time now, my mind is at 110%, and need to make this work. Otherwise I will be spinning a cardboard sign. Let me know what you want. Help support d-lab, see d-labelectronics.com

[@analogblues9606]

Yes, this is exactly what I’m looking for! You’re the best teacher to make the info understandable with great topics. Please continue. Thanks Terry!

[@d-labelectronics]

Thank you my friend, doing my best

[@audiotechlabs4650]

Terry, in the mid 60s, in Columbia. Mo., there was a similar TV repair shop called Peoples Electronics! Same setup…..old guy in a tiny shop full of equipment and customer’s repair items. Must have been 1000s of them across the USA! Before I became a “Solder Jock”, I would go in and have “Old Man Peoples” solder things like the old screw on mic connectors! I know exactly what you mean. For me it was better than an arcade! These training videos are great! Even guys like me can pick up tricks from them! Thank you for posting them! I hope you are doing well with the full time working in your own shop! I think it was very smart of you to do so! Love from springtime in the Rockies! Thanxz

[@mcaloon66]

I love the basic training series. Please keep it going.

[@darrenbird2526]

I absolutely love these tutorials. I listen to them all day at work, as a podcast! Might have to sneak somewhere, to be able to playback and watch a certain section! Thanks for taking the time to make GREAT videos Terry! Cheers from Tasmania Australia! Darren

[@albertcorkery2540]

Just found your page. I absolutely love it! Former US Navy electronics guy and guitar enthusiast. Your amp Basic Training series is so informative and your instructional skills are top notch. Going to watch them all. Thank You Terry!

[@preiter20]

This is excellent information Terry! Please keep these basic training videos coming!

[@handlethisyoutube]

Oh yes. This series is a great idea. Thank you Terry.

[@LitesLAB]

I love this series Terry! I would love to see some videos about combining tube preamp sections with solid state output sections.

[@shakeypeet]

God bless my man , been building for about 20 years now , I am self taught , and by reading and learning from other's , You my man are a breath of fresh air to some of us , so cheers , and enjoy your wine , well deserved teach ....

[@jdmccorful]

Yes, continue! Good stuff. Thanks for the look.

[@davehunt5706]

Do we , yessss we dooo 😀 Thank you Terry keep them coming !!!

[@mackfisher4487]

Memories of a kid at seven having Sammy our local TV repairman working on our Dumont TV he had two RCA tube caddies. Glad you're not turning Fred into a guitar amp. Terry I have no suggestions as to what content you should feature, but keep the hammered ham around.

[@chrischwaz7788]

This is a great series keep making them . Thank you

[@miguelrichartmellado2834]

Hi Terry! Thank you . This series is very important for my preparation of audio equipment. Always grateful. A hug.

[@kenk4555]

This is exactly the type of information I’ve been searching for. Thanks for sharing your knowledge in a straightforward and easy to understand way!

[@marknielsen8977]

Yes Terry. More of this type of content please.

[@300poundbassman]

Wow that was my dad's last cady he had. My father's Tv repair was from a bygone age. My Dad's name was Fred Nimmo. His tagline. Was "When your TV's dead see Fred". Nice touch!!

[@christominello]

I like this series. It’s a good second type of content.

[@MrMeik1970]

Perfect Terry 👍🏻 More Tips and Tricks please 🙏🏻 I like to see more Marshall Amps.

[@stevelueb7787]

Yes i want to learn more. Thank You, "Terry of Tube Guru"

[@edwardhannigan6324]

Hey Terry, great video and lots of info..Thanks for sharing, still learning..Ed..uk..😀

[@MaBaKar]

Thanks for this series, very informative.

[@ross3818]

Solving oscillation problems would interest me greatly.

[@mikiegood]

Love this series. Keep them coming. Thanks

[@d-labelectronics]

Will do Sir

[@zbaby82]

Yes Terry we love information. Maybe sometime when you are biasing a Marshall with EL34s you could show us the sine wave along with how many mV or mA via a meter the tubes are drawing. Thank you for your videos.

[@andrewmcwhirter2238]

Nice video, thanks! I would have liked to hear how "bad" the amp sounded with the unbalanced tubes (biassed so the hottest side dissipation was still within spec) after being modded.

[@richardweinberger2756]

Terry - I really like your basic training idea. I would be very happy to learn more about radios - I love tube audio too. Thanks :)

[@dirkfuchser737]

I allways enjoy your videos - Greetings form Germany

[@haywarddaryl]

Yes thank you! I would also love it if someone could teach me other audio equipment repair like preamps and car amplifiers. If only I had a neighbour just like you!

[@f.k.burnham8491]

Great info. This is data I need to fix these amps. Thanks.

[@tigertownmusiclab]

Awesome and excellent!! This is a great series!! Thank you.

[@Theoobovril]

Great, Terry, extremely useful piece of technical info'. many will find this very handy to know, more of this type video please.

[@Finom1]

Bless you Terry, you are an amazing educator:)

[@srtamplification]

In the first example, the variable resistor is being used as a potentiometer. In the second example, the VR is being used as a rheostat.

[@doitlickyoumeanit]

I think that a pot is a rheostat,...variable resistor,...

[@srtamplification]

@@doitlickyoumeanit No a variable resistor can be connected to create a voltage divider using three points (potentiometer) or can be connected using only two points to control the amount of current (rheostat). It has just become common to refer to all VRs as pots even though they may not be used as a potentiometer in the circuit.

[@TheFlyingRobert]

This is great, lots of good information here for rescuing these great old amps. Thank you!

[@theonewease]

Hi Terry! I think you should show us a Mod that gives us Both bias voltage and a balance control so we can use any set of tubes.

[@michaelhager4270]

replace the resistor on the balance pot with a trimmer set up as a variable resistor. one leg to ground middle leg to the balance pot.

[@josephmagedanz4070]

I think it is a good series...no matter what the topic, I always learn something new, so thanks for all your work!

[@audiotechlabs4650]

By all means….continue! You may hit upon common tube amp situations that can be fixed or reconfigured to make your tube amp be more reliable and work properly for all us ampaholics. Question….would you put a bias adjust pot for each output tube? That seems the way to match tubes exactly, no matter if they are matched or not? We are trying to make our amps the very best we can instead of mass producing several and we don’t care if it costs more money to do so! We are only doing one amp at a time, so what the heck. This new series of informative videos is fantastic, to share your knowledge with us! Thank you Terry and I hope being a full time solder jock will be enough to pay the bills and keep you in vino. Love from not yet spring in NW Colorado.

[@VashthStampeede]

Makes sense. I would love to hear the why nots on this great sounding idea. I have often wondered why no one does it that way.

[@kengevers8738]

The best bias system is to have variable bias, in addition to bias balance. That way if you have odd tubes, you can set the bias and get the other tube to balance. I think the S/F twin reverb amps were like that. 👍

[@ali2ndmail]

Love it! Exactly what I find useful to hear about.

[@fredcoston6580]

Wow , that was fast . Thanks so much. I've learned a lot from your d lab.

[@roncarter2188]

I love it Terry and need this information, thank you for all you do.

[@dominiquecerdan8255]

Terry you rock!!! Heck yea

[@openup007]

Great... perfect for the DIY electronic tech. I'd like to see a Fred & Terry (F&T) on high-voltage safety tips that will help educate DIYers on standard best-practices while working on high-voltage circuits. Thank you.

[@Bbendfender]

Great video. This helps me. I'm not a tech but I have maintained my Fender amps through the years by trying to keep them in good working order. I do have a local tech now who helps me when I reach a point that I don't know what to do.

[@juliochingaling5824]

Excellent video my friend. I ran into this problem on my 73 super reverb. Now I know it's a balance. A bias is a great 💡 idea. God bless 🙏

[@donbrock7885]

I think it’s great Terry Iv learned so much from you

[@fredcoston6580]

Yes , this is great info. Thank you. D lab

[@xtrchessreal]

😉I have installed a dual bias balance circuit. It this case you could have turned the one running hot down to level the other was running and extended tube life in these days of "No Tubes Left" We have to make use of these tubes until they actually fault and end their life. In general run tubes cool to moderate 55% to 60% dissipation and get many years of life. I think the idea of running at 70% is outdated for the times. Not arguing with you, adding in other options. I think this is a great series please keep it up. 🙂

[@firstchurch7543]

Excellent video, Terry. Most helpful. Also, it doesn't hurt for you to point out exactly where the parts go in the circuit. Thank you much

[@johnmac8084]

Yes Terry, this is useful, thanks

[@christyler9026]

Please continue!!!!

[@memorypalace8009]

Thanks for what you do.

[@CRUNCHCOLE]

Great video. I really need to learn how to read a schematic and translate it to the amp.

[@dankaptur6393]

This is great. Can you do a Basic Training episode where you discuss and demonstrate the way you solder to aluminum in some of your other videos?

[@wesleymatthews137]

TERRY, good stuff there. I’m curious if there is an option for a hybrid bias on that fender baseman. The best of both worlds…where the total bias can be adjusted and the balance of the bias can be adjusted? The ability Mai allow the owners to use tubes that are not as precisely matched?

[@giulioluzzardi7632]

I don't "fink" I know I need this fantastic and informative channel. Salute!

[@williamsmith4734]

This is what I been looking for. Keep this series going please. I been watching and taking notes. Thanks Terry.

[@daveogarf]

LOVE this, Terry! Practical lessons on common and less common problems. Thank you!

[@PhoenixGuitars]

Yes. Starting with sone basic fundamentals is great. Reckon in a pinch you could set the bias in between to get a happy medium? Thanks Terry!

[@scole901]

yes great series

[@tomasjones3755]

Thanks Terry; Fred, as well. I appreciate your ‘refiment mod’ vids. I also like your low power amp builds; actually, most all of it. Your vids are one of my inspiration & design tools. I’m about to repurpose an ’47 Admiral 6V6 single end radio. It has a stout PT & a sizable choke. I’m retaining the front glass & lighting the chassis, thanks to you

[@d-labelectronics]

Glad I can make a difference, Thanks for the comment, made my day : )

[@garysmith1532]

Keep the great content, never too many tutorials on basic amp faults which can be tricky to remedy..👍

[@RitusG]

I really enjoy this type of video. It always seemed to me it would be nice to have dual pots. One for each tube to dial in unbalanced tubes?

[@elgen0314]

Some amps have this and it is very convenient indeed

[@GonzGunner]

@@elgen0314 TubeTone Amps is one company that does. You no longer need to have a matched set. Very innovative, I must say.

[@MikeGervasi]

Yes. Also the amp build series I mentioned last video :)

[@ClumsyFlounder]

The intros for these basic training videos are top notch. Great info D-lab, keep it up brother

[@MrMrjauregui]

Hi Terry!, great video.. One suggestion: Could you do a video about your career? Those types of videos are always a success.. Best regards from Tecate, Mexico..

[@avcow]

Thanks for lessons

[@donaldfilbert4832]

Excellent !! Great clarification. I always wondered why some were "bias set" and some were "bias balance". Now I know !!

[@electrolytics]

Great stuff. Thank you D Lab.

[@waterknot1]

Great work! I think you meant "No way to adjust" not "No way to Measure" bias. You can always measure the Voltage drop at the Output transformer center tap to plate and calculate the Bias Current based on the Plate Voltage, Output Transformer DC resistance. I created an Excel spreadsheet that does the calculations for me. I suppose you could argue that directly measuring is better, but I've found calculated values are good enough for rock n' roll and usually match the measured current pretty closely. 🎸🎸🎸

[@parachuteman4]

Loved it. Thanks!

[@silvermica]

Yes, continue. I have a '79 fender twin that I repaired in 1989. It was my first amp. I still have it. I also have a few Orange Rocker amplifiers. The Orange Rockers all have scratchy pots (gain and volume). Cleaning them works for a little while - then the static/scratchy sound comes back in a few months. It's annoying. I thought maybe, somehow, a DC voltage sitting across the pot(s) might have been the issue. Pretty sure I checked with a voltmeter and found no weird DC voltage sitting there. Now, I'm wondering if these are just cheap potentiometers. I wouldn't be surprised if that's the case.

[@rciancia]

Good Stuff as usual Terry !!!!

[@pauldow1648]

I think I like your thinking. Sherlock like. You remind or inform how componet is supposed to work and point out how/why it is or isn't, then demonstrate corrective approach......

[@bigmac4948]

D-lab Basic training is an awesome idea Terry. “If you give a man a fish, you feed him for a day. If you teach a man to fish, you feed him for a lifetime.”

[@jerryogle8798]

Great video Terry. What about a video on your ratio meter?

[@dwightjt]

Nice job Terry on the stereo home brew. Your sore knees try some natural anti- inflammatories like eat foods with tumeric in them and garlic is very good for your knees your cholesterol and blood pressure a lot of spices you buy at the grocery store are healthy and anti-inflammatory will help the old arthritis good luck love your videos your friend Dwight from Allen Park Michigan.

[@ivanpowell8310]

Ivan Powell please continue

[@stevebrown4085]

Tell you what I think? I think you are going in a good direction. And I am sorry that I can not send you a bottle of good wine in the mail for your troubles being that I am not a distributor.

[@hardball107]

Hi Terry, I'm building a Super 6K6 from a 520. I have the filament circuit done along with the B+, it's pretty straight forward but I could use a review on the signal wiring from the input to the power tubes and output transformer. For me it's a little convoluted and instead of just following a schematic I'm trying to understand the path and function of the signal with tone, tremolo and volume controls. Might be a good subject for a mini class. Thanks, love the series.

[@mintmindofficial]

great series idea! i think alot of us that watch these types of videos are trying to learn this stuff but need someone to take it slow. i also think that most folks buy matched pairs or quads now so the hum balance pot has become somewhat obsolete and since more folks maybe want to save a few bucks and maybe want to try biasing themselves that a bias pot makes much more sense to have.

[@Bianchi77]

Creative video, thanks you :)

[@pauldavis6356]

Yes. Keep this content coming. Queation - you referenced the increase in wall voltage that we have these days and I can see how it can adversly affect tube bias - but do transister amps have the same concern? Should we be worried about output transistor bias with increased wall voltages?

[@Ian-jt2yz]

Terry, greeting from Canberra, Australia. I think I smell a rat, however this is very helpful. Tthanks for spending the time to do these. I look forward to them continueing.

[@DustInTheWindAZ]

They say there are no "stupid questions, so I'm going to test that theory. After watching this video, I'm wondering, "Can't you use a "hybrid" circuit that can both adjust the overall current (bias) to the tubes AND balance them, using 2 potentiometers? Kind of like having both volume AND balance controls on a stereo ( instead of a choice of one or the other)? Does that sound stupid? Being "noob", maybe I'm not using the correct terminology, but I think you get the drift of my question.

[@d-labelectronics]

Yes Sir, could be done

[@JasonTHutchinson]

Fender amps are easier to work on than some of those old Silvertones, etc. that have hot chassis.

[@robertkibbler1564]

Hi terry love the vids! Don't understand them fully but keep them coming. Do you ever work on Vox amps? Especially AC30 my 1963 hums bad am I doing it damage if I use it.....Rob from UK.

[@LoganFillmore]

Hi Terry! Thanks for sharing your knowledge with all us sinners. I've been listening to The Truth About Vintage Amps podcast too. Skip Simmons is a great amp tech in CA. Could you go over 12AX7 / 5751 / 12AT7 and their applications. I'm thinking of things like differences in current requirements, suitability for Phase Inverter uses ect. One last thing, should you have balanced triodes on a PI tube? Thanks!!!

[@elgen0314]

With all due respect, you could have changed the bias resistor for less than $1 and kept the balance circuit and the good old tubes in tact. I find the bias balance control to be very useful, although I seem to be in the minority. Adjustable fixed bias + bias balance control gives you the best scenario and you don't see that very often.

[@d-labelectronics]

Yes, I would agree both variable + balance would be the ultimate. The main thing to concentrate on is the idle current thru the tubes, They need to be set correctly of their life span will suffer.

[@VashthStampeede]

@@d-labelectronics Can you design a circuit that can be easily added to any tube amp that would serve the dual purpose? I have heard someone say that a guitar amp sounds better with a small difference in output tubes. Any truth to this?

[@elgen0314]

@@d-labelectronics Please let me clarify. Changing the value of the bias resistor will change the negative voltage applied to the control grid of the output tubes. This effectively raises or lowers the idle current draw of the output tubes. It takes 10 minutes and costs less than $1. You can retain the balance control and the mismatched tubes. Less cost, less bench time, more control over the circuit. Win-Win-Win. No need to buy matched tubes.

[@georgebush8038]

i would mind you making an adjustable resistor box and tuning grid resistors like brad (the guitaroligist ) for individual musicians.

[@johnnaighley9252]

I consider your new training series a good approach to the basics. It's helpful - you don't get more ignorant when watching your vids, far from it! ;-)

[@emmanuelgranatello1896]

Hi Terry, I love your channel! Quick question: is there anything that prevents having both bias level AND balance adjustment (with separate 2 pots, naturally)? Thanks and keep on !

[@d-labelectronics]

Can be done, Just did not go that far in this vid

[@kenzuercher7497]

Good description, Terry! By Bedford, are you referring to Bedford, Michigan?

[@doitlickyoumeanit]

I have no idea why my last comment was posted twice, and I feel like I didn't ask the right questions, or I didn't have enough info behind my inquiry. I also see that it will take me a little while to bring myself up to speed with you and your subscribers. I have a general knowledge of the function, of most of the components, but very little knowledge of how to put them together. I took basic electricity , in high school,...E / I X R , and so forth . What, besides a volt ohm meter, will I need to continue. I will take the chassis out again, so I can look for obvious problems and leaking caps. I appreciate any guidance you may have for me Terry, for now this is Kevin Keller saying I'm out of here.

[@danpearson2471]

This is great! Do you set bias to 70% of its rated value at idle?

[@waynemarc77]

LONGER VIDEO'S WOULD BE NICE...

[@Earlvis]

I have a ‘69 Super Reverb that’s blackfaced with adjustable fixed bias. I’m struggling with it because the bias adjustment no matter where I set it will not give me more than 10 ma of current per tube. I’ve replaced the bias range resistor, rectifier diode, 47/100 electrolytic cap, bias pot, several different bias pot resistors and nothing makes the circuit function properly. I’m at a loss at this point. 🤦‍♂️

[@TheDesertRat31]

Nice video. What pin on the power tubes does the 1ohm resistor connect to? It should be a precision tolerance, yes? I went ahead and got an extra multimeter (a pair of old USAF fluke FM/27s) to monitor both tubes simultaneously.

[@daveanderson5680]

Pay it on into the future