The ShermanAudio - Educational Series

This page concerns safety. This is for technicians who work on equipment energized by 100VAC, 120VAC & 240VAC. Yes there was a time when the safety of DC was exploited over the dangers of AC. Well AC can be more lethal than DC in a general sense. But all electrical shock or discharge can create current flow, through the tissues that comprise our biological bodies. There exists here a "potential" hazard of bodily harm. In our modern post industrial society, we live in an electrified world. So it behooves everyone in the world today to learn about Electricity. There are many different AC Power Standards on our planet, and they are all very interesting to understand and also good to know the differeces as a Traveler, makes you a roving McGuyver.

Lethal High Voltage Disclaimer

Tube amps can operate with lethal AC and DC voltages. All undertakings are always at the individual risks of the person working on equipment. I, as a personal, non-profit, pro-bono website, by the information I share, bear no responsibility for any such damages incurred by anyone. This is my digital Tube Amp diary, and by the fact that it is free, contains a great amount of useful practical information about Tube Amps and Electrical Measurements and Troubleshooting. If you want to get into working on hazardous equipment, you should take courses on electronics and safety.


Here are my notes on Safety, Workbench diligence, on-premise electrical & outdoor safety.

One can never have enough safety.

The focus should be on prevention.

Whenever anyone works with electricity, and taking medications.


If you are under medications that indicate not to operate machinery or drive

I don't recall where I read this, but it stuck like jumping Cactus.

"Clever people fix problems, wise people avoid problems"

The Importance of safety

Here are some important things to know, as we still live in the world of 12V Car Batteries.

So starting out with some practical simple examples here

My Website visitors may have never known the actual reason why of things electrical.

As an Electrical Engineer, I have made my share of electrical mistakes.

I have realized, after all the hours working with electricity

that, sharing information about safety, should be at the top of the list.

The learning curve of any hobby, should include safety.

Safety has to become an automatic habit, like making coffee in the morning.

Hobbies makes life much better, like Hot Sauce on Nachos

D.C. Car 12v Battery Tip #1


So.... why must we always first disconnect the Negative Car Battery Terminal, when changing a Car Battery.

To avoid a short circuit.

If you leave the Negative Lead in place and attempt to disconnect the Positive lead first with a non-insulated metal tool ,  and the tool happens to touch metal, when being pulled or pushed, You may accidentally have created a massive DC short circuit.

In less tha a few milliseconds of time, literally hundreds of amperes at 12 Volts DC can flow. This may even weld the tool to the metal, or, the battery can explode.

When installing the new battery, the reverse is true, Positive Lead first, then the Negative Lead last.

You never want to do the opposite.

By connecting the positive lead first, you are safely installing the first battery terminal connection.

The last pole to be connected is the negative cable, if the tool accidentally touches Metal, nothing will happen.

If you do the opposite of this, the likelihood of a short-circuit is no longer zero but a percentage greater than zero.

This is why safety plays such a key role in our lives, we should always be on the lookout for safety and potential hazards.

D.C. Car 12v Battery Tip #2


The reason why there is a specific sequence of jumping a Car. Also one must be very careful not create transient overloads in the electronics between the vehicles.

Older Points and Condenser Cars, did not suffer much risk from electrical transient issues.

Today's computerized cars, are best jumpered by a dedicated transportable battery charging and jumpering DC source or a Professional with the proper tools. If for any reason, you find yourself on the side of the road with a pair of your jumper cables, read this tip.

Caveat, newer Cars can suffer from electrical issues if improperly jumpered. And as with any such procedure, Car jumpering, like tire changes, are both risky things.

So the reason why we must never connect the last jumper lead on a Battery directly-to-the-terminal, you can create a "Spark" between the Jumper Cable and the Battery Terminal as you make the connection.

This is a Spark, that cound potentially ignite an explosion in the battery. Car batteries produce Hydrogen Gas, as in the Hindenburg.

Now a spark will not always cause a Car Battery explosion, but to zero out this percentage as a possibility is again about safety.

And safety is not like a Spice, you can never have enough safety in any recipe, just pour it on like Maple Syrup in Blueberry Pancakes, (does it seem like I am hungry?)

The proper manner to jumper a Dead Battery in a Car, is to first, be absolutely clear, on the circuit you are about to create.

Car jumpering requires that a known good donor battery, and a discharged battery be 'parallel' connected.

A parallel circuit is connected with a specific battery to battery polarity, this is absolutely critical for jumpering a car.

Positive to Positive

Negative to Negative.

and NEVER cross polarities!

Once you have your jumper cables ready, always protect the far end (discharged vehicle side) of the jumper by taking the Positive Clip and clipping it to the rubber insulation to avoid these clips of shorting when connecting to the donor Vehicle Battery.

Also, leave the far end of the jumper cables on a non-conductive surface such as the dirt road, asphalt, grass, sand, concrete, wood, etc.

Once the donor vehicle battery is properly connected to the jumper cable clips, Red to Positive + and Black to Negative -,  you can pick up, from floor, the deliberately pre-insulated end of the jumper cables you had previously safetly insulated.

You next connect the + positive lead to the + drained and failed battery terminal.

Next is the most important step, you have to make the Negative Connection to any available bare metal exposed part of the vehicle inside of the Engine bay.

Never directly to the Negative Terminal.

This is often tricky in the dark, but assures that any spark produced, will never have a chance to ignite a Battery explosion due to the distance of the spark and the Negative connection. If you connect this directly to the drained battery, you risk igniting an explosion if the drained battery is emanating Hydrogen Gas and the spark is a few inches from the Gas.

Safety is key Tip #3

Safety protocols apply to a workbench, any field work or any electrical system.

Learn to NEVER use both hands on or near any energized equipment to measure voltages or currents. Always follow the one hand rule.

Also, always discharge power supply capacitors if working on a piece of equipment, to avoid possible nasty, biting DC discharge shocks.

Sometimes a DC discharge shock can pass enough milliamperes of current through a human Heart and bye bye, or get first aid and live.

Never deliberately work on energized equipment. Forgetting to turn somthing off when working on it often leads to nasty shocks.

Life is already hazardous; Tailgaters, Road Rage, Accidents, Weather, so why add risk?

Never touch any unknown metal electrical panel, until you measure the potential to ground with a DC/AC meter.

Always take both measurements, DC and AC, as the Law of Superposition can strike at any time, in a bad way.

You see, any electrically energized system can have, simultaneously on the same wire, chassis or terminal, both AC and DC on the same surface (wire, post, PC Board) at the same time.

So to accurately measure things like Power dissipation, you need to calculate for both AC & DC Voltage/Current dissipation then add both the AC and DC Power Dissipations together Pac + Pdc, for the total dissipation in Ptot Watts .

I highly recommend that you always have a simple but effective AC/DC Voltmeter handy in your GloveBox, Purse, Backpack, etc.

AMAZON sells the ASTRO-AI meter for $12.99 ea. priced to order at least one for the home and one for every Car Glove Box.

You never know when a Car Battery will die, they can sometimes give you hints, when electrical systems on the Car behave strangely.

All Batteries seem to die at the most inappropiate time. You can also use it to test D, C, A, AA, AAA Bateries.

The short and skinny on small DC batteries, if the nominal voltage is 1.5VDC you are good.

A fresh one will have a voltage of 1.6 to 1.7V for a new good battery.

If a 1.5VDC battery reads less than 1.5 VDC, such as 1.4vdc, 1.3vdc, 1.2vdc..... it's on the way out.

Also change Batteries at least 2x twice a year to be safe, or every year as a minimum. Note that some batteries will leak acid, so if you aren't using the remote, take out the batteries, save the remote.

On properly Measuring Electricity

The safe way to take any electrical measurements is to prepare. Like throwing a Dart at a Dartboard, you have to concentrate.

Being careless, especially if working with energized circuits of any kind, think first.

A safe way to measure voltages when troubleshooting or testing is to always dedicate and connect the NEGATIVE terminal on the Metering Device to DC Ground.

This is usually best on the very first Power Supply Capacitor NEGATIVE connection terminal, or strip of you are lucky.

I nice and strong DUAL ALLIGATOR CLIP is wire is needed to firmly connect the NEGATIVE lead directly to DC Ground.

It is best to have a work bench dedicated for these things. But I have worked on Hammond Organs on premise and the work although rewarding, is not much fun after you do it for awhile.

I prefer to make new stuff, than to fix stuff. But I have become a good troubleshooter of electrical issues. After all I learned by working as a Technician for the first 5-8 years of my career, then I went purely into Engineering.

Proper soldering iron, wire, and all of the nice to haves like a illuminated Magnifying Glass Mechanism, A anti-static bench mat, a Anti-Static Wrist Strap with a Button to the Anti Static Mat.

A nice long, protected AC power strip and a slew of test equipment....

A anti static floor mat/rug, and finally Anti Static shoes. This is the best overall basic setup. Then you add test equipment.

I like to have all of my tube testers out and ready, as I never know what kind of test I need on a particular day and time.

So use an alligator clip, or you can temporarily solder a wire jumper to Ground or create a good adapter to make a secure firm connection to DC Ground.  Soldering a wire is always the best method to get a good DC ground when working on equipment, and far outweighs the down side of soldering on a terminal, big deal.

Make sure that the Black (Neg) ground lead connection is also out of the way and does not tangle with your Red Probe Wire.

Use only one hand when measuring Voltage or Current, the other hand should be in your pocket or held away from the equipment.

This same safety principle applies to any electrical device such as a Breaker Panel.

Use only ONE HAND to unlatch any electrical panel door.

The act of placing both hands on unknown metal surfaces, can potentially create a current path through your Heart, and only a few milliamps can be fatal and stop your Heart from beating properly.

Interesting Residential Electrical note

The reason why 120VAC - 0 - 120VAC  (L1 - N - L2) residential and commercial "Bi Phase" AC power exists in some countries, so the likelihood of a 240VAC Shock is minimalized. A person who dwells in a U.S. Facility, Home, Office, will only ever have a 120VAC shock, if a mistake or accident should happen. The only way to accidentally receive a 240VAC shock is by actually "touching both HOT leads L1 and L2". This is why the US 240VAC Mains is split into two 120VAC Phases, for safety. Hence the term Split phase, or Bi-Phase. You would literally need to pull off the cover of your Breaker Panel and deliberately touch both L1 and L2 rails at the same time. A 240VAC Shock is far nastier than a 120VAC Shock, and believe me I know, from when I was a Teenager,replacing the Power Cord on our Range

Electrical Theory & Music Technology

I have never been able to understand how a hobby like HiFi and Audio has become fraught with

all kinds of ideas and misconceptions. Electrical Theory is absolutely the basis for everything related to music

reproduction using active and passive components to create Amplifiers, Buffers or Preamplifiers.

Sometimes I visit other forums like Motorcycles, Cars or Hunting and cannot read the nonsense that I come across

on Audio Forums.

People, if you want to learn, please pick up a Calculator, Pencil and a Book.

Nothing in the realm of Voltage, Current, Power and Energy comes easy.

Opinion has little effect on the laws of nature and physics.

Learn resistor color codes, read about how Capacitors and Inductors work.

Spend time on a schematic and trace the signal flow with colored marker.

Be able to explain how to convert AC to DC.

Learn basic DC/AC Theory, how a Power Supply works.

Learn what Regulation is and how to Calculate it

Learn how Diodes & Transistors operate, Shockley's Equation, Ebers-Moll equations

Learn how a Vacuum Tube operates, and learn each Tube Type.

Learn how stuff works in general, even if it's not electrical.

Realize that troubleshooting electrical problems, takes years of practice and experience.

You cannot just wake up and fix stuff.

Buying old Tube Amps on Ebay is not for beginners

Usually you buy one, and expect it to work.....

Personally, I have rated the equipment

I have worked on on this Website, in the Classic Amp Section...

with a rating of a level of difficulty from 1 to 5

Please, also learn Ohms Law, Kirchhoff's, Norton's and Thevenin's Theorems.

It will help you become a keyboard jockey

Who actually make sense and contributes to the whole.

Learn the safety aspects of changing out a Car Battery,  like which "pole" do you remove first?

Why do we have to clamp the Negative end of the jumper cable, to the dead battery Vehicle's chassis

and not directly to the Negative Pole?


This is how our ancestors learned not to walk up to a Tiger in the wild and Pet it.

Why Children and Paper Clips are a hazardous combination

Why the US Electrical Grid uses Bi-Phase Power in Homes, and not just Single Phase 240V like Europe?

Do you know what Phase means?

What is more dangerous a 120 Vac shock or a 240 Vac shock?

Many of you would be surprised at the opinions and ideas people have when asked this question.

and here is the reason why

 120V is safer than 240V for residential AC power... rant on.......




This hobby is hazardous when you start to tinker with Mains Voltages and High Voltage DC.

Numbers speak facts, not opinions or ideas, this is the bottom line people, reality is not based on beliefs.

This is so for all disciplines, and that is why we call them disciplines.

They take focus and dedication to learn stuff the right way

There is nothing that you cannot learn, that can be as valuable as the knowledge of Math and your Hobby

And for most people, Math does not come easy, it did not for me, it was my worst subject, after English.

Once you can visually manage basic mathematical relationships, a veil lifts, as you apply these to your hobbies and life

Math can help us become visual mathematicians.

We can become adept at looking and coming up with basic figures visually.

Algebra.... as you were saying in High School:


A = B*C, A = B2/C, and A=B2*C

The Square Root Algorithm

The Quadratic Equation to solve for

y = x2 + x + 1

Slope, Graphs, Limits, Exponents.....

To be given A and C to Calculate B?

Remember the name of your High School Algebra Teacher?

Most Math teachers never explain why you are learning these symbols, and that was a let down, I agree.

Practice formulas, until you memorize them, and can visually calculate when given simple whole numbers.

V=IR, P=VI, P=V2/R, P=I2R

When you can manage the very, very basic and fundamental relationships above

You map them to Schematics and the veil starts to lift.

You will understand your environment better, and your quality of life improves.

Most Audio Forums  lack the Sun of knowledge

When you have then earned your knowledge, you are not just repeating a Google search result

Something basic like a set of Christmas lights, is a simple Voltage Divider circuit.

Then learn to draw out a Voltage Divider, neat stuff.

You will understand and can explain ands draw why pulling out one Lamp, makes the whole set turn off

A voltage divider circuit.

What is Voltage division? Current division?

 Learn about Time Constants, Attenuation, Amplification factor, Low-Mid-High Frequency Analysis

Op-Amps and Regulator Tubes and IC's

Plan to design and build your very own 12V Power Supply at home, handy.

Then when you pick up a schematic, those symbols will start to make sense

And you will realize that it is just a roadmap you are navigating

The closest thing to compare this to is a Piano or a Guitar Fretboard

A similar effort is needed to learn them well.

So what are the fundamentals?

Learn about Voltage and KVL

Learn about Current and KCL

Learn about DC Power and AC Power Factor

Learn Current Node analysis I1 = I2+I3

Learn Voltage division analysis Vt = V2 +V3 +V4

Learn how to calculate Series and Parallel combinations of Resistors, Inductors and Capacitors

Learn why very old Tube Equipment did not use a Power Transformer, and these Amps were called Widow-Makers

There is a very cool place called knowledge where 70% of Forum Experts have never visited, or cared to.

A Smartphone is not a College Degree, and don't ever believe the lies that that a Degree is useless.

Unless you study the lifecycle of an Antarctic bacteria with no chance of ever visiting Antarctica.

We have to be practical and wise, and this has nothing to do with academics, it comes from our Parents.

Once the Fog of opinions and endless forum conjecture (some insults) lift, you will realize how amazing an electron truly is.

You will automatically tend to visit less Audio forums, and seek true knowledge

That Math class now makes more sense that back in High School !

You will begin to shake your heads when you read posts, but instead, order a few good books.

You will chose not to add to posts, as putting facts, generates hate and weird comments.

It is all in our minds, and the care and feeding of this our most precious resource, our Brain

the fundamental way to also take good care of our ears and protect our hearing for life.

Then you will move on to Alternating Current analysis and also Signal Tracing.

Once you learn how to use an Oscilloscope, you will become a good fixer of Audio Circuits.





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