Repair Safety First

[mykey]

It occurs to me that while teaching so many to work on tube amps and even solid state amps that so little has been said about safely working on these amplifiers.
A shock as little as 32 milliamperes can stop your heart from beating; and with so many killed by electrocution every year, now is the opportunity to add your safety tips and rules.
First let me remind you that a tube amp stores quite a bit of power in it's filter capacitors, long after the amp is unplugged. Before working on one of these amps the power supply(s) should be discharged- learn how BEFORE starting your repairs.
So then with that in mind, please take electrical safety seriously; and not as a bothersome formality. Many have categorized safety rules as a joke.
I would hope that the more experienced techs post their safety tips here, and that the learning techs read and follow these safety tips.

[mykey]

On Jun 14, 8:10 am, Jim <a...@beforeyousend.com> wrote:
> Patrick Hoelscher wrote:
> > I am interested in learning to build my own guitar amp. Possibly a tube amp
> > or hybrid. I am a Computer Science graduate with a small amount of
> > electrical engineering knowledge. What is the best way for me to learn? Buy
> > a couple different used amps and take them apart?
>
> A very good way to start is to buy an Epiphone Valve Junior and modify
> it. You can also buy an old hi-fi or PA and modify it. Old stuff needs
> more attention, such as replacing filter caps.
>
> DO NOT proceed until you understand HIGH VOLTAGE safety issues. Filter
> capacitors can store enough energy to KILL YOU, even with the amp off
> and unplugged! Always discharge the filter capacitors first, and I keep
> a lead between preamp plate and ground while working on a dead circuit.
> Learn the "one hand rule" when working on a live circuit. It's WAY
> different than computers or modern electronics.
>
> I have two yahoo groups that might interest you. The Epiphone Valve
> Junior mods site is by invitation only. You need to post your real
> E-mail and request an invitation. In that invitation, you must convince
> me you know the safety rules.
>
> The "open enrollment" site is:http://launch.groups.yahoo.com/group/guitar_amplifiers/
>
> ALL are welcomed at this site. General discussion on guitar amplifiers
> WITHOUT personal attacks, religion, politics (the usual alt.guitar.amps
> NONSENSE).

[Amp Kat]

Certainly you want to practise safety in amp repair but it's kinda like an Indy race car driver. Before they get in the car they are aware that they can be killed at any time or any wrong move. Same here so if your scared you may be shocked don't work on it. I also stated a while back that different people have different resistances and capacitances in there body. So it may kill this guy but not kill the other and of course othere medical issues that could cause something fatal totally objective in someone else. That being the case I should be dead because I've been hit with everything from 1 to 1000 AC & DC and I'm still here but what is does is give you respect for where your touching and what your grounding yourself on. I'd be willing to bet that there are some damn experienced techs out there that still get shocked even with the precautions and experience they have. And don't even tell me you never get schocked because if you do I know better. You are aware that some capacitors will recharge themselves even after discharged if there aren't discharge resistors across them so discharging isn't always as safe as it seems but yes it is a good idea and very easy and quick to do. Still not a reason to keep newbies from working on their amps but most of the ones I've seen are aware of the dangers before they do it. Do you have some numbers on the people that get killed every year working on guitar amps ?

[Rob Mercure]

Mykey,

You might want to review the Forum archives and the old Ampage archive to see how strongly we've stressed safety over the years - especially with one topic that reoccurs periodically: working on/restoring old line connected guitar amps. I dunno, I do you hope take this in the spirit I offer it but you seem to offer us strong opinions/facts intended to be helpful - and they are - without realizing/researching that we've addressed these again and again over the past decade +.

As far as electrocution hazard it really isn't the voltage but, as you noted, the current flow that kills and some folks with naturally low skin resistance have been killed by as little as 60 volts accidentally applied to a wet chest - and all of us who have serviced TVs sometime in the past have a tale, or a dozen, describing how we were "knocked" across a room when we accidentally encountered the ultor of a CRT or, if old enough, the HO plate cap, et al. KB noted how caps can "recharge" themselves over time and since a CRT is nothing but a big cap anyway when unpowered I've been "bitten" more than once by 30 KV, or so, that developed across a picture tube when the clip on the bleeder slipped off.

My personal gremlin has to do with safe grounding and I won't let an amp leave my shop unless it has an intact properly grounded cord with both the fuse and the switch in the hot side of the line.

Oh, and I'm glad you mentioned the "one hand rule" - can't stress that often enough (especially since I work in hot electrical panels often). But I really worry more about an inexperienced "technician to be" forgeting to unplug the piece of equipment under repair and electrocuting themselves across the mains input than I do from any residual "B" supply. The "newbie" probably has some idea that tubes involve higher voltages and may be a bit on guard while completely forgetting that his little solid state practice amp is pretty directly connected to his friendly neighborhood lightwater reactor.

And thanks for your "invitation" - I'm sure that we all appreciate it. One thing that I've treasured about this group/Ampage from the start is the lack of flames, ego dogfights, personal attacks and emphasis on solidly backed technical information instead long rants in support of whatever fad modifications are in vogue.

Take some time and get to know us - while we can be a bit "laid back" if not lethargic now that summer has heated up for those of us north of the equator - we do strenuously emphasize safety related issues and tend to be "one big happy family" (especially since that last lobotomy "took" - was running out of scalp - <grin>).

Rob

[mykey]

no, I won't pretend that experienced techs don't get shocked because we know they do. and a large portion of those killed are the pros who should know better and have let their guard down.
the tendency of a capacitor to charge itself is referred to as the chemical charge. the capacitor will slowly charge itself up, even after sitting unused for years, and even when there are discharge resistors across it.
what are some of the favorite methods for discharging power supplies before working on an amp?

[mykey]

Originally Posted by Rob Mercure

Mykey,

You might want to review the Forum archives and the old Ampage archive to see how strongly we've stressed safety over the years - especially with one topic that reoccurs periodically: working on/restoring old line connected guitar amps. I dunno, I do you hope take this in the spirit I offer it but you seem to offer us strong opinions/facts intended to be helpful - and they are - without realizing/researching that we've addressed these again and again over the past decade +.

I am glad you have stressed safety, and I am bringing it up again just to keep the thought of this fresh in people's minds. And to remind those who have just started the adventure of amp repair and tweeking.
In fact there should be a separate safety category in this forum, just to remind everyone, every day.
I have repaired amps for 34 years, especially tube amps, and we need to pass what has been learned, along to those in particular who have just started doing this.
repair safety cannot be a part time job, it must be job #1.

[Steve Conner]

Well, Ampage may be a big happy family, but for better or worse, it's also part of the Internet. The Internet is huge and open to anyone with a computer and a phone line. You don't have to sit any kind of exam to get on there.

So on Ampage, like on any forum, you will encounter a bewildering range of people, from hardened techs like Enzo all the way down to the kind of simple folks who would happily clean their sneakers with gasoline by the light of a candle. While smoking a cigar.

What I'm trying to say is that many people who read this board are probably so dumb that they will ignore any safety warnings we post and kill themselves anyway, and then their moms and dads will sue TBoy. I read the other day about some guy who climbed into a power substation with a hacksaw and tried to cut off some 132,000 volt busbars to sell for scrap. While they were turned on. Did he notice the Danger Of Death signs and 15 feet of razor wire? Did he have the slightest conception of what 132,000 volts at a couple of thousand amps does to human flesh?

In the light of this, I don't even bother with safety threads on forums. I think they are more of a liability than an asset: what if someone posted safety information that was wrong? or could be spun as wrong by a cunning lawyer?

If I were TBoy, I'd post a prominent disclaimer saying that all information on Ampage is provided without warranty and any liability is disclaimed, and leave it at that. In fact he probably did that already, I hope.

Your safety is not someone else's responsibility. It's yours. Use common sense at all times. Educate yourself. Don't do something just because you read it on the Internet.

[MWJB]

Jumper wire from a preamp tube pin to chassis - as long as you can see it there (and it's been there more than 30 secs) you know you are safe, no worries about caps recharging.

If you KNOW that the amp you are working on has first stage filters wired in series with smoothing resistors/as a totem pole (if you don't know, refer to previous paragraph), always verify that the standby is in the "ON" position. Leave for a short while (I put the kettle on and make a cup of tea, by the time it's boiled, you're safe. Coffee works just as well). Again, easily visually confirmed, caps won't recharge and much reduced risk of suprises later.

[drewl]

I like getting zapped.....wakes me up.

[R.G.]

Originally Posted by mykey

the tendency of a capacitor to charge itself is referred to as the chemical charge. the capacitor will slowly charge itself up, even after sitting unused for years, and even when there are discharge resistors across it.

Actually, if you think about it for a minute, this is impossible. If capacitors could recharge themselves to any significant extent with appropriately sized discharge resistors across them, it would in effect constitute a source of neverending electricity.

Capacitors do have dielectric absorption and chemical effects absorption, but both of these are successfully kept to below any reasonable danger level by properly sized bleeder resistors.

What is "properly sized" is the next question, obviously.

I designed power supplies for a living for a long time. We were required to demonstrate that every capacitor in the power supply was safely under 42Vdc and 10J of stored energy within 10 seconds of the main power being cut off irrespective of the normal load. That's a pretty stiff requirement. But 42V and 10J was what the international safety regulations said for our commercial computing equipment.

F'rinstance, if you have 47uF at 500V on your B+. Voltage out of a cap declines at V= Vo*e^(-t/tau) where tau is the time constant, R*C. So we have to have 42=500*e^(-10/R*C), which gives us ln(42/500) = -10/R*C, or
R = -10/C*ln(42/500) = 85.898K
Since E = C/2*(^2), the cap at full voltage has E = ((47E^-6)/2)*(500^2) = 5.9J, we don't have to sweat the stored-energy requirement.

For a cap with an 86K resistor across it, to hold the voltage to a dangerous level (i.e. over 42V) the cap has to supply 488uA FOREVER to get that much voltage to appear across the resistor. That's 20.5mW coming out of the cap FOREVER to get even 42V across the cap plus discharge resistor.

I promise you, that does not happen. If you remove the discharge resistor, either accidentally or on purpose, the cap may well recover some charge that had been stored in chemical or mechanical distortions of the dielectric; and they do. But the constant current-eating of a discharge resistor will keep up with the slow rate of recovery of the cap from this kind of recharge.

As a general practice, mounting a 100K bleeder resistor across every high voltage cap in a fashion that will not reasonably let it come loose will guarantee that the cap is bled down to safe if not zero voltage levels. Having a discharge resistor on each cap with each cap separated by a dropping resistor also gives protection against all single faults of bleeder and/or dropping resistor. 100K does not meet the 42V in 10S rule, but then we're not designing space shot stuff, and really it's difficult to get your hand on a cap within 10 seconds if you don't already have the thing on the bench in front of you.

That doesn't mean that bleeders make it safe. But they do remove some of the hiding-rattlesnake danger of charged caps.

By now you have guessed my favorite way of discharging caps - put a bleeder on them and wait.

[Enzo]

Hey, I have a hacksaw. Are power stations easier to rip off than construction sites?

[bob p]

Originally Posted by Rob Mercure

As far as electrocution hazard it really isn't the voltage but, as you noted, the current flow that kills and some folks with naturally low skin resistance have been killed by as little as 60 volts accidentally applied to a wet chest -

Trivia time. The types of currents that most of us are familiar with fall into the range of what is defined as macroshock by the medical community. Thanks to the high impedance of dry skin, when you're looking at 120 VAC / 60 Hz power, it takes about 1 mA of current to reach the threshold of perception, and more than that to hurt you. 5 mA is regarded as the maximum harmless current intensity.10-20 mA falls into the "let go" range, where you still have voluntary muscle control and you can purposefully remove yourself from the current source. Any currents that are higher are bad. Very bad.

In contrast to macroshock levels of current, people can be killed by microshock, where currents of as little as 20 uA can cause ventricular fibrillation / cardiac arrest. Susceptible people would be those with pacemaker wires, or external conduits that are in direct contact with the heart. Those people are susceptible to electrocution from very "minor" problems, such as stray capacitance buildup on the chassis of a piece of equipment with a faulty ground.

For this reason operating rooms are required to have non-conductive floors, isolated AC power lines (with no direct connection to ground), all of the equipment has to be chassis grounded (to the supply side), and line isolation monitors are in place that will alarm if a faulty piece of equipment were to be plugged into the line. In the event that a faulty piece of gear were plugged into the isolated line, the decreased the impedance from the isolated line to ground would set off an alarm, and you'd have to start immediately disconnecting equipment until the offending piece of equipment was identified and the alarm condition was resolved.

I often wonder why people who are talking safety when working on tube amps don't mention using isolation transformers for the equipment under test, and clamping a dedicated ground lead onto the chassis when they go inside of the amp. A redundant low Z path from chassis to ground is a beautiful thing.

[Enzo]

I don't use an iso on the tube amp chassis because it won't have any effect on the high voltage getting to me or not. I can be just as dead from having the isolated 120VAC coursing through my inner fluids. And all the other voltages like B+ and stuff are with respect to chassis, so that doesn't change.

And I am not sure how the difference between voltage and current on the body helps. The point is to avoid contacting it, whether the voltage or the current is what actually kills you is - seems to me - irrelevant. I mean having that knowledge tells me to make exactly what changes in my procedures to make me safer?

[mykey]

Actually, it's happened with as little as 12 volts...don't even need 60. just depends again on skin resistance, how well the body "hooks up" with the current.

Originally Posted by bob p

I often wonder why people who are talking safety when working on tube amps don't mention using isolation transformers for the equipment under test, and clamping a dedicated ground lead onto the chassis when they go inside of the amp. A redundant low Z path from chassis to ground is a beautiful thing.

The more experienced will preach isolation transformers, but more commonly used while working on TVs- for tube amps really an excellent suggestion. ground fault breakers not a bad idea either. This whole set up, variac, current meter, isolation tranny, GFI breaker, clamp on ground lead, could be built for about $200 with some scrounging. There are the GFI breakers with a higher trip point for motors that still afford you some increase in shock protection. A safe work area will have a rubber mat to stand on because after all your feet can ground to the floor just as easy as your hand touching the chassis.

[mykey]

Originally Posted by Enzo

Hey, I have a hacksaw. Are power stations easier to rip off than construction sites?

Forget the saw Enzo, be a man and use your TEETH.

[Dave Curtis, dB AudioTech]

Originally Posted by mykey:
"the tendency of a capacitor to charge itself is referred to as the chemical charge. the capacitor will slowly charge itself up, even after sitting unused for years, and even when there are discharge resistors across it."

Originally Posted by R. G. :
"Actually, if you think about it for a minute, this is impossible. If capacitors could recharge themselves to any significant extent with appropriately sized discharge resistors across them, it would in effect constitute a source of neverending electricity."

That's mykey for you. Ask him about aluminum increasing resistance with age, or how a 10,000uF cap on a tube rectifier is a good thing. Massive grain of salt required. -DC

[Rob Mercure]

Mykey,

While I respect the time you've put in repairing amps - I've got around 37 years in and Enzo, Bruce, Ray and other have much more time while Steve and some others are "genuine" Phd Engineers - you somehow don't seem to consider your posts/responses before your send them.

Do you understand how a Ground Fault Circuit Interrupter works? It really doesn't give a rodent's rectum whether there even is a ground connection - what it does is compare the current in the hot conductor to the current in the neutral conductor and if they differer by more than a few mAs then the circuit "assumes" that the difference is flowing to ground - hopefully not through a person - and trips! So one can easily get their hand across the secondary of a PT and have nice brown smoke coming out of their ears while the hot and neutral currents remain the same - even if some of that current is leaking into the chassis ground if it's being drawn equally through the PT primary you're fried. And, of course, an isolation tranny makes the situation worse as the primary and neutral feeds to the iso will balance even if the secondary currents aren't doing so. Oh, and this also means that a GFCI protects a two wire - "double insulated" tool as well as the older metal cased ones.

Again, I'll credit you with your long experience in modifying amps - but some of use have run/are running out own businesses and service shops and can bring much practical experience to the table. I hope you can work with us to add to those experiences - ain't nobody on this forum, as best I can tell, got anything to prove. We've each got our strengths and weaknesses

Steve: Remember that you can never make anything "idiot proof" enough to stop a sufficiently determined idiot <grin>.

Rob

[mykey]

Originally Posted by R. G. :
"Actually, if you think about it for a minute, this is impossible. If capacitors could recharge themselves to any significant extent with appropriately sized discharge resistors across them, it would in effect constitute a source of neverending electricity."

capacitors definitely recharge themselves, even after years of standing idle. and the process is very slow, not a very good source of everlasting electricity. the point is that you can be shocked by one even when the power supply has been unplugged for a very long time, even when there are resistors across it, and plenty have been shocked this way.
coincidently I think in many cases a 10,000 mfd capacitor in a power supply is a great idea, and so do several other amp builders. perhaps you are referring to the minimum recommended capacitive filter to use with a rectifier tube. this does not rule out using a much larger capacitor. some would prefer eliminating the 60 cycle noise in amplifiers, reducing ripple in the power supply to the most minimum. or when building a DC heater supply for a high gain tube amp 10,000 is about the LEAST I use. just because you don't pay attention to 60 cycle noise does not mean that people who do care about reducing noise are stupid.
this also means that Jim Macintosh, who used 4700-10,000 mfd caps in his tube amps is also stupid, and that other manufacturers such as Levinson, Yamaha, Krull, Crown are all idiots. After all who would waste the money to filter a power supply enough to remove the 60 cycle noise? what idiots! Just think -60 cycle buzzzz in your amp does not matter anymore, because Dave Curtis said so.
And then while your at it, call Sprauge, Cornell Dubleer, and other capacitor makers, and tell them to stop making these wasteful unnecessary capacitors, because Dave said we don't need them anymore!
Reality is quality low noise amps have very big capacitors for very low noise, and if we want to build them that way, we do not let thick head know it alls tell us different. We want low noise and we will build for low noise.
We will continue to use DC heaters (like Macintosh did) and 10,000 mfd capacitors not because we are stupid, but because we are more intelligent, and we demand a higher standard than PV repairmen.

[Bruce / Mission Amps]

Mykey:
"...you can be shocked by one even when the power supply has been unplugged for a very long time, even when there are resistors across it, and plenty have been shocked this way."

I'd like to see some documentation of anyone getting shocked from a filter cap that mysteriously recharged itself... that is pure bunk.

Mykey:
"perhaps you are referring to the minimum recommended capacitive filter to use with a rectifier tube. this does not rule out using a much larger capacitor.
I think in many cases a 10,000 mfd capacitor in a power supply is a great idea, and so do several other amp builders."

Jeeze Louize... Not with tube rectifiers and a standard tube amp setup. Of course it rules out using absurdly high value filter caps.
And what is this "minimum recommended capacitive filter to use with a rectifier tube" statement mean?
Have you recently read a tube manual with respect to a tube rectifier and a capacitive filter vs inductive?


And speaking of the rectified B+ rail.... what 60Hz noise are you raving about?
You need to recheck out how FW or FWB rectifiers work.
By the way, the AC filament supply runs at 60Hz... but in 99% of other DC supplies, like the high voltage B+ rail from that rectifier tube we were discussing, ... it does not.

I think most of this is basic electronics 101 but maybe you are so far beyond most of the builders and home brewers here you've forgotten much of this.
Nah!!

[mykey]

Originally Posted by Bruce / Mission Amps

I'd like to see some documentation of anyone getting shocked from a filter cap that mysteriously recharged itself... that is pure bunk.

the chemical charge of batteries and capacitors is a fact.
there is no mystery to it, the construction and dielectric chemicals in the capacitor will cause a charge to be accumulated, slowly.
a car battery is shipped dry. when installed the acid is added to it, no charging required, the battery will come to full voltage without charging. this is also an effect of the chemical charge.

[R.G.]

Originally Posted by mykey

capacitors definitely recharge themselves, even after years of standing idle. and the process is very slow, not a very good source of everlasting electricity.

Sir: Caps don't charge themselves. They are an energy storage device. They can only put out what was put into them at one time or another. If they continued to leak out electricity more than we had put in, we'd call them batteries.

There are two mechanisms to longstanding charge: dielectric absorption and chemical dielectric change. However, these two mechanisms can only put out what was stored into them. That was the point of my illustration - to try to point out that you can't get out more than was put in. I think I shot too high.

There are two limits on this energy. (1) the total energy that can be stored that way and (2) how fast it can come back out. If (1) was even 1% of the total energy stored in the cap, we'd never use that kind of caps. The stored energy is **TRIVIAL** compared to the total energy in the cap. Not that it's not detectable or doesn't happen, but it's vanishingly small compared to the working energy of the cap. It can also only go in and come back out at some rate. The reason that caps can accumulate a charge after being discharged is that the energy stored in the dielectric by both mechanisms leaks back out into the "usable area" of the cap as stored voltage. If there is a resistor on the cap that can dissipate the stored dielectric energy as fast as it comes out of the dielectric, the stored energy in the cap and hence its voltage must remain zero. The resistors eat it all.

But I can see that you're not going to let this go. Show us some numbers. Give references and verifiable facts. I can do that for each of my points. Can you?

the point is that you can be shocked by one even when the power supply has been unplugged for a very long time, even when there are resistors across it, and plenty have been shocked this way.

Can you produce some references to (a) electrolytic caps as used in tube amps (b) with bleeder resistors across them all the time (c) shocking someone? Please let us go read them.

coincidently I think in many cases a 10,000 mfd capacitor in a power supply is a great idea, and so do several other amp builders.

Apropo of what? I like purple caps, I think they're a good idea too. The issue is always how do the work? I think a stack of 40 car batteries would be an even better source of B+ than a transformer/rectifier/filter, especially in terms of surge current and hum. That doesn't make it a particularly practical thing to do.

perhaps you are referring to the minimum recommended capacitive filter to use with a rectifier tube.

No, I wasn't. But then, there isn't a minimum recommended filter to use with a rectifier tube. There is a clearly stated MAXIMUM first filter cap for many rectifier tubes. That's there because bigger caps make for bigger pulse currents in rectification and big enough pulses overcomes the emission capability of the rectifier tube's cathode. But I've never seen a recommended minimum. Can you show us where a minimum is stated for a cross section of tubes, not a maximum?

this does not rule out using a much larger capacitor. some would prefer eliminating the 60 cycle noise in amplifiers, reducing ripple in the power supply to the most minimum.

No it doesn't. Not wanting to ruin rectifier tubes quickly is what rules out using much larger first caps. After the first filter cap and some isolating element like a resistor or choke, you can go for all you can afford. But the first filter cap is what determines what the pulse currents are and that is what needs to be limited to give decent rectifier tube life. SS diodes can use first caps as big as you can fit in and afford precisely because their repetitive pulse currents are huge compared to tube rectifiers.

Then there's the whole issue of ripple in power supplies. I bet the same "some" would be confused looking for 60Hz ripple in a full wave rectified power supply. That's because there isn't any. It's 120Hz, produced by the folding nature of the full wave rectifier. Power supply caps can't reduce 60 cycle ripple. They reduce 120 cycle ripple. The rectifier gets rid of the 60 cycle.

or when building a DC heater supply for a high gain tube amp 10,000 is about the LEAST I use.

Huh? When I'm building low voltage high current power supplies I use caps as determined by the math to get ripple as low as I need it to be. In many cases, it is cheaper to use smaller caps and electronic regulation than to brute force it with caps, but each to his own, I guess.

just because you don't pay attention to 60 cycle noise does not mean that people who do care about reducing noise are stupid.

Who says I don't pay attention to 60 cycle noise? I *do* know where 60 cycle comes from, and it's not the DC power supply. And you know, I don't recall saying that anyone was stupid. Can you play back my quote and show me where I said that?

this also means that Jim Macintosh, who used 4700-10,000 mfd caps in his tube amps is also stupid, and that other manufacturers such as Levinson, Yamaha, Krull, Crown are all idiots.

You think so? I believe those are your words, not mine.

Reality is quality low noise amps have very big capacitors for very low noise,

Did you mean "low power supply ripple"? Because big caps don't affect the 60 cycle noise at all. In fact, big caps don't reduce thermal noise either. Or rather, can you explain to us HOW big caps reduce noise as opposed to power supply ripple.

I can, in fact, tell you one mechanism that big caps have for CREATING more power supply noise. It's that rectifier-pulses thing again. Those big pulses are not sine waves; they have significant harmonic content and they can both radiate directly and excite RF resonances in the wiring and ESL of the caps to radiate bursts of RF that the rest of the amp picks up as line frequency buzz. The bigger the cap, the worse the buzz. What helps here is not big or little caps, but good wiring practice and snubbing.

and if we want to build them that way, we do not let thick head know it alls tell us different. We want low noise and we will build for low noise.

Just you inside, smart, determined guys like McIntosh, Levinson, yada, yada, and YOU???? That's a pretty elite club you're in there, fella. You're right - don't listen to anybody that has a different opinion, because you and the low noise mafia there have it all sewn up.

We will continue to use DC heaters (like Macintosh did) and 10,000 mfd capacitors not because we are stupid, but because we are more intelligent, and we demand a higher standard than PV repairmen.

Just you few smart determined guys, eh?

Every so often a guy hits the pockets of the internet that renews my sense of amazement. Most recently it was walters/markphaser. But I think we have a new contender.

[Amp Kat]

Originally Posted by R.G.

Every so often a guy hits the pockets of the internet that renews my sense of amazement. Most recently it was walters/markphaser. But I think we have a new contender.

That's why when I first saw the post I thought he was a troll and still not completely sure he's not but unlike the other two who I believe had some disorders this one still in Limbo.

The 10,000 uf seen in those Hi-Fi 's even though tubes, could also be for the low voltage supplies. I'm not sure I've ever seen a 10,000 uf cap over 250vdc and that is computer grade and as Bruce pointed out the tube rectifier isn't going to like anything over 33uf much less 10,000uf. I really enjoyed that math on the discharged cap scenario RG so it wasnt' to high for some of us. FWIW I've never seen over 12 volts on a resistor discharged setup and many times much lower and correct also that they won't charge back up to full plate supply voltage but enough to give you a good tingle if you go across them when no discharge resistors are used and powered down with the standby on or no HV.

[Enzo]

Crown makes tube amps? Wow, learn something every day.

[mykey]

Originally Posted by Enzo

Crown makes tube amps? Wow, learn something every day.

i think i was referring to the fact that several manufacturers use 10000-20000 mfd capacitors in amplifiers and that the reason these are used is to obtain quiet operation, peak demand reserve, maximum ripple rejection in the power supply. i do not recall that i ever said crown makes tube amplifiers.
i continue to maintain that there is no fault in reducing power supply ripple in any amp tube or not, by using 10000 mfd capacitors, particularly in DC heater supplies. While some may except loud 60 cycle buzz in guitar amps (example mesa boogie) I do not except the noise. Many recording studios and musicians appreciate this standard of low noise.
In fact i will give you another reason to make fun of my high standards, i have used 1 fared (100000000 mfd) capacitors in some mixing consoles, succeeding in reducing noise to immeasurable levels, after many before me had failed miserably. Of course the only ones who appreciate this are the studio engineers and owners those who love PVs will not.

[R.G.]

Originally Posted by mykey

i think i was referring to the fact that several manufacturers use 10000-20000 mfd capacitors in amplifiers and that the reason these are used is to obtain quiet operation, peak demand reserve, maximum ripple rejection in the power supply. i do not recall that i ever said crown makes tube amplifiers.

Your sloppy use of reference and hyperbole implied it, and not just to me.

This is a largely tube amp forum, and the discussion was about tube amps before your reference. If you had said something like "in solid state amps, DC power supplies can use caps as big as 10,000uF" then we would have understood that you didn't mean that Crown makes solid state. We would have said something like "Well, duh." because we all know that these amps use big value caps as a given.

You're not the only one here that has a decade or two fixing amps, fella.

i continue to maintain that there is no fault in reducing power supply ripple in any amp tube or not, by using 10000 mfd capacitors,

If you next say "in the first filter position after a tube rectifier" which is what the context of tube amps implies, you mark yourself as someone who does not understand tube rectifiers. That's what your posts implied.

particularly in DC heater supplies.

That's fine. Well, duh. That's not a particularly good flag to wrap yourself in. It provides you no cover.

While some may except loud 60 cycle buzz in guitar amps (example mesa boogie) I do not except the noise. Many recording studios and musicians appreciate this standard of low noise.

You then make the leap that the people you're talking to don't know what they're talking about, and that the fact that they don't understand what your muddled train of references means implies that they have a love of 60 cycle hum. You flatly miss the item which was explained to you slowly and in detail that 60 cycle hum does not and can not come from small caps in power supplies, miss the fact fact that it's 120 cycle ripple that power supply caps reduce, and somehow turn this explanation of fact into a group of people demanding high levels of hum in recording studios.

That is, you're trying to deflect criticism by blaming us for having sloppy standards when in fact you completely missed the accurate technical explanation of the inaccuracies in your posts. This little trick works pretty well in sound bites for the newspapers, but it doesn't work at all for a technical discussion with people who know what they're doing. Give it up, act like a man and admit you muffed it.

You seem to not understand that further assertions of poor you, misunderstood by naive, dull, and misinformed us will only make you look worse in this forum. This particular group does know what it's talking about. You might possibly know what you're talking about and might even have something to contribute here, but you are being sufficiently defensive (and offensive, too) that you're tarnishing whatever value you might have here.

In fact i will give you another reason to make fun of my high standards, i have used 1 fared (100000000 mfd) capacitors in some mixing consoles, succeeding in reducing noise to immeasurable levels, after many before me had failed miserably. Of course the only ones who appreciate this are the studio engineers and owners those who love PVs will not.

Again, get off it. You're dealing with a knowledgeable audience and wrapping yourself in the flag of "my high standards" only makes you look silly.

Let it go, contribute where you can, and quit thinking of the rest of us as uninformed. The longer you don't do that the worse you look to the group here.

[Amp Kat]

Originally Posted by mykey

Of course the only ones who appreciate this are the studio engineers and owners those who love PVs will not.

I worked for an Audio Co. for 6 yesrs and we visited many professional Studios. I've seen Engineers that know what their doing build low pass,high and band pass filters from scratch and have seen one pull his complete Studer down himself and recap every E-cap (bucket full) in the whole damn thing every five years. Didn't need 10,000uf caps to reduce noise just a simple change. You can only get DC so smooth to where it has no effect on noise at all. Peavey amps ? Why not ? They aren't used for recording only playback and good engineers put all of their money into the console,speakers and killer Mic-pres and products like LA1,Summitt and have Neuman U-87's and an awesome array of tube and dynamic mics. The least thing they need is noise reduction gear and in fact I talked to an Engineer the other day that told me one of his secrets was adding noise to the mix so I find what your saying hard to believe.

[bob p]

Wow. This thread got interesting while I was away for a few days.

I wanted to add something about the GFCI and isolated supply topic.

Originally Posted by Rob Mercure

Do you understand how a Ground Fault Circuit Interrupter works? It really doesn't give a rodent's rectum whether there even is a ground connection - what it does is compare the current in the hot conductor to the current in the neutral conductor and if they differer by more than a few mAs then the circuit "assumes" that the difference is flowing to ground - hopefully not through a person - and trips! So one can easily get their hand across the secondary of a PT and have nice brown smoke coming out of their ears while the hot and neutral currents remain the same - even if some of that current is leaking into the chassis ground if it's being drawn equally through the PT primary you're fried. And, of course, an isolation tranny makes the situation worse as the primary and neutral feeds to the iso will balance even if the secondary currents aren't doing so. Oh, and this also means that a GFCI protects a two wire - "double insulated" tool as well as the older metal cased ones.

Rob is right about how a GFCI works -- very small hot/neutral current differences in the range of 5 mA can be detected, and the GFCI will open the circuit in a few milliseconds. That's why the National Electrical Code requires GFCI placement in outdoor and potentially wet locations. They interrupt the circuit when "harmless" 120VAC currents on the order of 5mA are detected. As I mentioned in an earlier post, 5mA falls into the macroshock category, and a properly functioning GFCI will open a 120 VAC circuit before the current level is enough to become threatening to someone who has an intact high-Z skin barrier.

To keep things in context, its important to note that when you think of a GFCI, you need to consider that its calibrated to open the circuit at currents that are safe with 120 VAC potentials, not rectified High VDC tube power supplies. The GFCI protects you at 120 volts. Step up the voltage and you're dealing with energy levels that are outside of the realm of the GFCI.

Another thing to consider is that a GFCI provides absolutely no protection against microshock. You won't find one in a hospital operating room; Even though the voltages there are 120 VAC and the potentials are in the range of function of a GFCI, because of the absence of high impedance barriers, the lethal currents are orders of magnitude lower than the sensitivity limit of the GFCI. In that type of environment a GFCI is not used because the patient would likely be dead long before a GFCI ever sensed a problem.

Back to the subject of isolated power systems, there seems to be a little confusion about this with respect to ground potential references. In a non-grounded system an isolation transformer does not increase the shock hazard -- it actually decreases it. In a true isolated power system, the room is not grounded. Its possible to stand in a puddle of saline solution and stick your tongue onto one of the Hot 1 or Hot 2 isolated high voltage lines without getting zapped. That's because the floor that's soaked in an electrolyte solution bears no continuity to ground. Because you're not contacting the circuit at two points you don't complete a circuit and there is no current flow.

When a faulty piece of equipment is plugged into an isolated power system it does not present a shock hazard. It simply converts the isolated power system into a conventional grounded power system, and thereby removes all of the protective features that the isolated power system would have otherwise provided. When this happens, there is a marked reduction in the impedance between Hot 1 and ground or Hot 2 and ground. The line isolation monitor would quickly detect this condition and sound an alarm to alert the staff that a defective / hazardous device is present in the circuit and is presenting an active electrocution risk. (that dangerous piece of equipment immediately gets disconnected and sent to the techs, who presumably know how to work on it without killing themselves.)

Alternatively, if you're not dealing with life support equipment and you're willing to tolerate circuit interruptions, the LIM in an isolated power environment could be replaced with a GFCI on the secondary side. In that case, the GFCI would trigger and open the circuit when it sensed asymmetric current flow. But you still have the problem that the GFCI is pretty useless, as it trips at currents that are way too high for patient safety. The key to understanding this situation is to understand how ungrounded/isolated power environments work. Admittedly, this is something that is out of the realm of what most people are familiar with in their day to day lives.

Going back to Rob's tube amp example, if you're working in a true (intact) isolated power environment, you can stick your tongue onto the B+ rail and you won't complete a circuit unless 1 of 2 things happens: a) you concurrently touch the grounded chassis, or b) there are already leakage currents in the defective amp, and they have converted the isolated system into a grounded system. In that case, all of the conventional rules of safety still apply.

[Euthymia]

Originally Posted by mykey

....so little has been said about safely working on these amplifiers.

Many have categorized safety rules as a joke.

Are you referring to this forum? Here, safety is talked about often, with great seriousness and if someone shows evidence of inexperience in a post, they are warned about brushing up on safety issues before going any further.

....with so many killed by electrocution every year....

Yes, in the hundreds. What were they doing when it happened? Working on tube amps? Probably not.

a large portion of those killed are the pros who should know better and have let their guard down.

Statistically true, but the kind of "pros" they are is usually construction, utility, or farm workers. How many appliance repair people zap themselves?

There is a risk of electrocution when working on guitar amps. It does not need to be overstated. Doing so just makes the poster look pedantic.

[mykey]

I believe you would not need to to this with a Studer, but in huge consoles such as StudioMixer which have such pathetic decoupling, thin wires, and long distances it works tits! Also consider the tiny little power supplies these things come with that are installed internally.
You could tell a lot about the noise in a console just from the fact that the power supply is external.
You will also get a laugh out of this: modifying mixers so that the frequency response is 3-1000,000,000 hz. Sorry I think the FCC might be a little upset about that. we call this the "air sound". The engineer I recently did this for said it made his $4000 Levinson preamp sound like a joke.
So there, now you have some more rumors to spread about me.
I won't go into too much detail about the Marshall clones with $10,000 sets of custom made silver mica Cornell Dubleer capacitors, Teflon circuit boards with gold plated terminals, aircraft grade silver/ Teflon wire, 2 parts per million aerospace resistors, $425 sets of Bugle Boy output tubes (all grids matched and heaters too). Not just the plates and current guys, ALL the grids AND heaters.
That would be too much for you guys. You don't believe it? Call Richardson Electronics and Cornell Dubleer and ask them, go ahead! You think this is crazy? It's more than that, it's DERANGED.

[mykey]

some prefer to discharge capacitors by shorting them to ground (kablam)
some say that this wrecks the capacitors, and that these should be slowly discharged through a resistor over a period of time. Some like working with the capacitors charged and don't give a damn. What would you say is the safest for the capacitors? Have you ever heard this, shorting the cap to ground wrecks the capacitor?

[R.G.]

Originally Posted by mykey

I believe you would not need to to this with a Studer,
...
You think this is crazy? It's more than that, it's DERANGED.

Mykey, you're doing it again. As I said:

That is, you're trying to deflect criticism by blaming us for having sloppy standards when in fact you completely missed the accurate technical explanation of the inaccuracies in your posts. This little trick works pretty well in sound bites for the newspapers, but it doesn't work at all for a technical discussion with people who know what they're doing. Give it up, act like a man and admit you muffed it.

Originally Posted by mykey

some prefer to discharge capacitors by shorting them to ground
...
Have you ever heard this, shorting the cap to ground wrecks the capacitor?

Mykey, you're doing it again. As I said:

That is, you're trying to deflect criticism by blaming us for having sloppy standards when in fact you completely missed the accurate technical explanation of the inaccuracies in your posts. This little trick works pretty well in sound bites for the newspapers, but it doesn't work at all for a technical discussion with people who know what they're doing. Give it up, act like a man and admit you muffed it.

Just ignoring an invitation to discussion technical matters in detail doesn't mean that your audience will let the issues slide.

Could you please address some of the issues I asked you about, like proving any of your assertions? The more blathering in general you do, the more I think you don't know what you're talking about and are casting around looking for something to deflect the issues.

You're still digging your way down.

[Rob Mercure]

I was initially patient and tried to give you the benefit of the doubt - which you chose to totally ignore. So, if you're trying to state that anyone can modify an audio mixer to have a high end - even at say, 6 db down (you do understand the "bel", the "decibel" and a logarithmic scale) - that reached a gigaHertz (you do understand that three zeros is thousands - kilo, six zeros is mega - millions, and nine zeros is giga - billions, I hope) then I believe that you equal, if not tie, the most full of shit post/reply that I've seen on this board! We've all tried to tell you gently and reasonably so I'll just be an ass and state: Why don't you go back to whatever junior high school classes you're missed and not try to "impress" us with your ever deepening doo doo!

I'm pretty sure that your favorite way of discharging capacitors is to connect one terminal to each of your ears!

[Enzo]

Mykey, the FCC doesn't care in the slightest what goes on inside your mixer. As long as it doesn't RADIATE radio frequencies, it can MIX then all it likes.

The very concept of a mixer or any other audio product having a bandwidth of 3-1GHz is simply ludicrous. It would serve no purpose, and have the undesireable side effect of amplifying rumble, noises, and RFI.

ANd if you are going to throw around brand names to impress us all, for God's sake at least spell them right.

[R.G.]

I think I really have been shooting too high with mykey.

It could well be that he's actually naive and is just trying to be impressive. He's missing some very important techie items that should be in his background that should be in the kit of anyone who's fixed stuff for as long as he says, and the ducking any technical confrontation is pretty damning.

I'm always a fool for taking someone at their word until they start saying stupid stuff. I know that the conservative position is to consider everyone a liar until proven truthful, but I just don't do that well. It's such a pessimistic position.

The bigger issue may become - how do you get him to quit polluting the water?

[Alex/Tubewonder]

Originally Posted by R.G.

The bigger issue may become - how do you get him to quit polluting the water?

Starve him, just ignore his cries for food