Super Electronics Troubleshooter- Working On Hybrid Technology And Not Destroying It 

To learn more about electronics in a different and very effective way, and at the same time support this channel, go to Mr Carlson's Patreon page, click here: www.patreon.com/MrCarlsonsLab

So great that there are no jump cuts, no crummy background music, just clear patient presentation

You are a natural born teacher. I've been troubleshooting for a lot of years but I always learn something new from your channel.

You bring so much knowledge to the world, Mr. Carlson. I go on a journey on each one of these videos!

Thanx very much. Have worked in electronics for many years mostly with tv and vcr. The tip you gave about the coupling with the scope is priceless.

never thought of the charge that's kept in the DC blocking caps. now it's so obvious. many thanks from germany!

Special thanks for making this video as I have a Legend 30. It has not work in years. I tried to fix it and gave due to time restrictions. I might after watching this video might try it again. Jeff Healy played this when he was in my studio in Vancouver BC in 1987. So it is special to me. Jeff passed in 2008 but his style of playing lives on in RU-vid. Thanks again B

Definitely enjoy your videos. Brings back memories when I worked on aircraft electronics in the US Air Force in the 1970's. Oh yes, some of the technology was vacuum tubes. This was the APN-59 radar systems prior to converting them to solid state circuits.

Mr. Carlson, I consider you a genius! Your confidence is overwhelming. You are a geek's geek! Thank you for sharing your knowledge and experience. I am in a financially challenged situation and would like to become a patron but cannot. For you to share videos with non-patron viewers is tremendous. Thank you and I will be looking forward to your next RU-vid post. I have an 70s Peavey PA head that works but is noisy, crackling and hiss and would like to repair it. Maybe sometime in the future make a video on noisy ICs or transistors and how to repair them. Thanxz

I now know that it's so important to learn how to read and follow any diagrams you get as it can easily throw you off. I struggle to follow the circuits printed on a page and what it actually looks like. Many thanks love the lab!

I'm an electrician and have been working in electronics for a while and just recently started repairing tube amps, and hybrid amps, and electric guitars. So this is good stuff! I knew about meters carrying a charge when testing caps, but not tubes. It makes sense that the meter would apply voltage but wow! that's a lot!.

It didn’t take me long to subscribe and it didn’t take me long to join your Patreon. I’m learning so much from you and others like you that are sharing skills and knowledge for the price of a cup of coffee. I’m so grateful 🙏

Mr. Carlson, I'm learning so much from your teaching, especially the "traps", like always discharging your probe before checking an IC. Also, I actually know why I'm building a kit oscilloscope now! Thank You!

Absolutely love your channel I didn’t know about the hybrid trick of discharging your scope before working on the solid state Mike

I signed up for the Patreon page. Just the tools alone you can build make it worth it. The additional content though is invaluable if you like hobby electronics and repairing older equipment.

I am learning so much from your videos , thank you keep them coming , your friends from New York City

He is a outstanding teacher. Wish he were my teacher back in the day. Please continue to spread your God given gift.

That's a great video Paul, I think grounding the probe, is the best bit of advice I've heard in a long time, it's now written on a piece of card above me at the bench, probably just good practice all the time working on any thing, Thank You. Paul

Thanks for sharing with us. I am more of an electrician, so these things help me to expand my knowledge in an area that I know a little about, but could use more in. Thanks again!

Knowledge is most powerful when shared freely. Cheers for the upload, you're a true scholar.

Excellent video as usual. I f I were to add one thing, that would have been to DC couple the scope and show the AC portion riding atop. Drive it hard and watch how the AC fills more and more of the DC span. Thank you for sharing.

Your knowledge and presentation are amazing. As usual, thanks for sharing!! Love the tube amp related videos.

I admire your knowledge and professionalism! Very nice overview and lesson.

Ah Hahhh ... a light at the end of the tunnel ! Very valuable info. All these years and I never knew the probes stored a charge. I feel stupid now but somewhat enlightened. I'm no engineer, no secret there. That little gem is worth a paycheck alone ! Thanks a million.

Good thing you are honest. I know few techs who would claim the amp couldnt be fixed and it would have to be trashed. They would offer to buy it for parts then fix it and sell it.

Yo the wood on that cabinet is beautiful! Thanks again for all the tips! The $2 is totally worth it.

I have found simply wax in many devices against shattering and so. In warm environments works well. And thankyou for bringing back my memory about this discharging the probe before fumbling in the ICs or transistors. In the 80s we hat to look for this. 73 from Germany.

such great knowledge !!! thank you. i have a late 90's Crate amp that sounded great but one day i was playing & the sound volume just started to slowly decrease, just like you was gently turning the vol. pot. to 1. when the volume went low, it didnt go silent, i could hear the guitar, but very faint. now, if i turned the amp mains AC off, and came back later or the next day, it would power up , and play normally . but after about 15 min. the sound would slowly fade, just as before... keep in mind that i love the sound/tone this amp has, so i didnt give up... after checking the fuse had continuity, i came back once a week & would turn it on & try different things ,such as; used a different guitar, cord & played without the onboard DSP , next time i used no Dist/OD. the amp has 3 channels. i would play on each one at different volume levels. i was relentless in my hopes that the amp wasnt ruined & i had lost my $500 investment. after a few months, kinda giving up on it, when the volume faded, i angrily gave the top of the housing a "whack" with the side of my fist.. not real hard . AND the volume instantly resumed . but after 5-10 min. it would fade out again. another fist bump & it worked then fade. after a few times of that, im thinking a loose connection. so i gathers my tools & gently opened it up, visual inspection= no burned componets or PCB's , no swollen or leaking Caps , i made sure all jacks & pots were tightened. what i could see looked ok. but it had ribbon connectors to outboard PCB's and to get to the underside to look for lifted solder pads was gonna be more involved that i felt capable to do. the amp is a Crate GLX212 . i still have it & it will still sound great for 15 min. i stopped the fist bump... i wish you was local & i could afford to pay you to diagnose it & possibly repair.. i think it is fully SS. i didnt see any tubes. sorry for the long comment, i did say i love this amp & i havent found any helpful info until i seen your vid of guitar amps.. thanks again

Thanks Paul. You likely will save me and others from ignorantly destroying components. Keep these type of precautions videos coming. J K

I'm pretty sure the chip you pull at 32:45 is the legendry RC4558 chip used in the first version of the Ibanez TS808 Tube screamer, amazing! The guitar nerds will know what I'm talking about.

I'm really enjoying being a Mr Carlson Patreon! Great content, Paul. I'd recommend others to give it a try - there are various levels you can choose from to fit your needs. Supporting this really awesome channel and teacher has, for me at least, been a wonderful return on investment. Highly recommended!

The JRC 4558 is the famous tube screamer chip , found in the TS 808 overdrive pedal. Nice video.

Man I'm waiting for you to restore a Hammond organ, I'd LOVE to see you bring one back to life and improved!

Another great troubleshooting tip Paul. Thanks for sharing.

Back in the 1970's I worked on a lot of TTL logic, no high voltage problems like this, but the TTL was +5V, and there was also + and -15 Volts for Op-Amps...we had these clips you used on the 8-14,16 pin DIPS that looked sort of like a big clothespin...it got the pins spread out and helped prevent shorting when probing around.... When I first started that job-1970, we were still using Simpson 260's but soon progressed to Tek-Tronics scopes ...There was 90 volts and 120 volts DC for the X-Y-Z axis drive motors on the NC machines, but pretty well spaced away from other components...lots of General Electric systems. Still all those voltages appeared on the same PC boards.

Hi Paul thanks for the great tips as always! Have a safe and great day friend. Alex.

Very interesting video. Ah yes, the venerable 4558, those are everywhere, along with younger siblings the 4559 & 4560. Depending on the architecture a solid state amplifier can run full blast into an open. Since they're mainly current amplifiers without a load they don't dissipate much power. As long as it's stable, no oscillations or nonsense, it'll just sit there. Another choice for either glass or silicon is a moderate load. One could test with something like 800 Ohms. With tubes you can drive it a bit harder than into an open but still have decent sensitivity for delicate measurements.

I just successfully repaired one amp after blowing up 99 guitar amps prior. I just found out 99 ways how not to repair an amp. Thank you sir. Keep up the good videos.

I didn't know about scope probes "storing charge". VERY helpful.

My hats of to you sir your are good at electronics i learned from the USCG love the way you work !

thanks for your tec tips every video I watch from you is a new lesson thanks for your time!

I have a Legend amp sitting in storage, can’t wait to go through it. I just sub’d and liked, you have a new fan. 10/10

This is such a good tip. Thanks as always Paul,,, good stuff.

Mister thanks for the tips !!! oh yeah it's a gold nugget .... Never before i'm hearing that and now i'm sure about AC and DC discharging on the ground by the probe !!! good day for you .... and Happy new year mister Eric from France.

Thank you for all your time and sharing of your knowledge.

Another great video! Do you plan on doing a video on troubleshooting a DC coupled guitar amp? Discrete DC coupled bipolar transistor amps are especially difficult to diagnose because an issue in a previous stage can upset a later stage to the point that the later stage will burn out, etc.

Great video as always...such good information delivered well :) Thank you for all your work & sharing of your skill set.

Thank You! I would not have thought of the AC coupled scope

Great video! I started in electronics back in 1980 in the USMC. In all these years, I’ve never come across your tip on charging up the probe coupling cap. That was a very interesting demonstration. I’m curious, what is the maximum dc voltage you would measure with a 10x or 1x oscilloscope probe? Do you go strictly by the rating of the probe and scope input? I’m always paranoid about blowing out the input to a scope, so I bought some diff probes (20/200x) and a HV probe (1000x) for working on tube circuits, but I’m thinking that’s probably overkill. My scopes say 300 or 400V peak, but for some reason, I wouldn’t feel comfortable applying that much voltage directly to the inputs.

This is a very clear explanation like all your videos! I have a question for you: Sometimes I fix old audio gear. I am thinking about replacing all OP amps with newer ones, especially when the old ones are 741 that where fine in the 70's, but are considered crappy sounding and noisy today. If I look at the data sheets to find OP amps that as a higher slew rate, lower noise and is internally compensated for unity gain, can I be sure that the circuit will not get into oscillation?

I'm not trained in electronics, but I've been watching your videos, hoping to learn something about how amplifiers and the components within them work, and I'm finding your videos very interesting and informative. I have a question - I've heard you mention how there's a difference between how an electronic technician and a musician look at their amplifiers. The last time I brought my, what I believe is an all-tube amp (a Dean Markley Signature Series CD-60 Combo) to someone for repair, he swapped out the 8 ohm speaker that was in it and put a 16 ohm speaker in it instead. When I asked why he did that when I went to retrieve the amp, I was told because he "liked the way it looked on the scope better". What I have always wondered since then is, is it safe to change back to an 8 ohm speaker (as the speaker output jack is labeled that the amp was designed for), and was this just a case of him looking at the amplifier from a technicians point of view, judging by what his equipment was showing him...? or would the amp, as he claimed, be more "unstable" if I were to put an 8 ohm speaker back in it...? I'd be interested to hear what your thoughts might be on this...

I noticed that spring reverb unit is nearly identical to the ones used in the Hammond console organs - mainly the earlier A, B, and C series models. In fact, it reminds me of my last teardown of a C3G console.

Thank you for this excellent tutorial and advice Paul. I would like to ask if you forget to ground the probe after checking the V-tube, could this dangerous charge carry to other channels of a scope or are they insulated ?

What an interesting video ! Thank you a lot.

Thanks again Fine Sir. I always learn things frome these videos

Great video, I am going to build the discharge capacitor from patreon now!

It's worth noting that on some scopes (such as my Tek 2225) switching the coupling selector to "GND" (which grounds the input) will drain that capacitor (at least according to the manual). Tektronix even had the foresight to put the ground selection between AC and DC coupling on the same switch. Trap for young players I guess

This Channel is "Awesome"!!

Your an awesome teacher Sir

Thank you from Croatia, very nice !!!!!

I love these videos. I might just learn something....

Brilliant, Just another epiphany, Destroying components, while troubleshooting.

That just makes sense, thank you kind sir for sharing!

So what he's saying is the quality of a Legend is just a Legend?....

Very Nice video again!! The best from Oslo Norway!

Thank you for another excellent video.

BRAVO, well done!!!!!!

Hello Paul, enjoyed your presentation.

really am digging your channel, please more musical equipment repairs! As an amateur musician/guitarist and at home recording engineer LOL who isn't these days, right? I use so many electronic devices every day, I am so ready to learn to repair or modify/build my own equipment ( Fender Bassman tube guitar amp clone ;)) last month I took in my guitar effects/amp digital modeling device (helix) for repair and was told the wait was at least two months or longer to get it back if they could find the issue and then get the parts and repair it, that is another reason why I am signing up for your course through patreon but my big issue is I have a condition called essential tremor meaning my hands can shake slightly to very badly when I actively use the muscles which makes fine handwork like soldering nearly impossible at times or using small screwdrivers etc. Do you have any ideas of what I could use to help with this? In my day job, I am an aerospace manufacturing engineer specializing in advanced composite materials I don't have trouble in my work which is mainly on a computer typing albeit slowly and at times not very accurate but I manage to get the work done and still can kick out some jams on my electric guitar

You mention the benefit of silicone as an electronics friendly and non oxidizing adhesive. Which specific brands do you recommend for this application?

Could you tell me what type of diode I would need to install a signal light buzzer on my wife's Triumph motorcycle. I have a beeper from a Honda Goldwing, they used a double pole relay. I need a diode to control a load of 2 12v 3-5 w bulbs. The diodes are needed to keep the voltage from feeding back up the wires to the opposite signals, that would make them 4way flashers. Sorry it's not a electronic question but I need info on what I have to find....Hal

I'd like to know what you use as a contact cleaner? I have a Dynaco SE10 equalizer with very noisy sliding pots.

Very interesting that the scope probe holds the HV charge from the vacuum tube plate and must be grounded before probing a semi conductor component. Is there that much of a reason to build hybrid circuits in the first place? How old were you when you became interested in electronics. I was about 4 when I stuck a flashlight bulb into a light bulb socket and a big spark turned my fingernail black.

Thanks for sharing this. Great Info.

this is gold. thank you.

Fantastic information Paul, thank you for sharing. Would it be correct to say that it would be a good practice to always ground out your scope probe before putting it to a different point? I know it's not always necessary but if you developed that habit, can you think of a situation where it would NOT be a good thing to do?

another great video,as usual...!!!!

What about the metal cans in the middle of the chassis? Are those voltage regulators? I know a few people who have built their own guitar amps with oddball valves (common and cheap enough because they were pulled from old TVs and radios), but how often do you encounter a commercial guitar amp with anything other than jellybean valves and op amps with standard pinouts?

if you have ground lift in oscilloscope how you can discharge probe ? What is better put oscilloscope on isolation transformer or is better connect amplifier to isolation transformer?

You've piqued my curiosity about the probe charge. Is this charge within the probe itself, internal to the scope or perhaps a bit of both? I wonder now if you could dc couple the signal with the scale set appropriately. Would the scope trace the discharge when you ground the probe? I'm unclear as to how you would trigger it. Maybe it needs a storage or recording scope to capture it?

Great troubleshooting information

You mention using a signal generator to test with scope. How was the sig generator connected up to amp?

i have been watching your vids and subscribed to your patreon site I am working on a blown peavey guitar amp there are two trace blow out I need some more info on what could cause board trace to blow , a short to gnd was what I thought but that checks out do you have any ideas or vids that can help.

The RC4558 is a G.P Opamp . The TL072 has lower noise.

I wonder are those integrated circuits all the same, if so and one gets popped what about replicating the Op-Amp with discrete components until you can get replacement chip.

Excellent! Thank you!

Thanks Mr Carlson lab loved it.

you say the distortion the amp makes is a harsh sound, but i think the technical term for it is a kickass sound

this is good for as many teaks as possible to know

Totally great video! Can I ask something, In the previous video 6L6 tube has a coil stopper, why this amplifier did not? Thanks Mr Paul.

Holy crap! I would not want to be sitting in your chair when those shelf brackets give up.

Yes! I remember All Electronics selling those mechanical reverb units in the mid 80s for a short time. Never ordered one though. :/

Do you actually need a capacitor discharger or could you just unplug the unit and power it on/off a couple times ?

I don't know the complete history of the Legend amps but I do know Billy gibbons used one on the Eliminator album. There very loud and well built amps

Hi Paul, could you talk more about the use of contact cleaner (27:53) in potentiometers? I was looking into doing this on scratchy pots a few years ago, and as usual on the internet, everybody had an opinion on what product to use, and whether it was a good idea to use solvent when there might be grease inside the pot. Some said that any benefit would only be temporary. Could you comment on your experience with this? I appreciate that you might not want to get into contact cleaner brand names. Thanks!

Mr. Carlson, I'm something of a tube guitar amp nut. When I replace Fender (Mallory) filter caps in amps from the 1960s, the old ones very often measure close to twice their rated capacity with zero ESR. Are they really acting as capacitors of those readings or is there something else going on? I ask because my favorite amp "seems" to sound more sterile since replacing the filter and bypass caps throughout. All were dated 1964 and they all read 50~85% higher capacitance than labeled. Many thanks for your opinion on this. I would expect a change in the tone/sound, but surprised that it might be a less desirable tone after doing reasonable maintenance. Thanks

thanx for sharing any explanation as to why or what causes the scope to charge like a capacitor

A lot of contact cleaners contain very aggressive acids in order to do their job. It's always a very good idea to wash the parts after cleaning with an adequate liquid. The manufacturers of contact cleaners themselves recommend this. Leaving the acid on the cleaned parts will eat them up in very little time.

The late 70's and 80's saw a push by the industry to get musicians to accept solid state amplifiers. This saw some degree of success by companies like ROLAND and PEAVEY especially in jazz and country music where a clean tone was needed. But despite years and years of engineering , marketing, and return trips to the drawing board, solid state amps have never achieved the status of tube amps in rock music. Randall is the only manufacture to have major touring rock acts use solid state amps (a few exceptions not withstanding) Hybrid amps were an attempt to approve the tone by either making the preamp tube (like LEGEND and some MUSIC MAN) or making the power amp tube section tube (like the PEAVEY Classic). Point is solid state sections are widely recognized as a trade off in tone for a lower price and higher reliability in rugged applications. I have NEVER heard a musician say he chose a solid state amp for the harsh distortion tone! Great cleans? maybe (PEAVEY Renown series - ROLAND Jazz Chorus)

39:52 Teased so many times... and finally the release.