HINTS!

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1.  Speaker connections, if done wrongly, can DAMAGE your amplifier.  The most common cause is shorted wiring inside a 1/4" plug or touching/shorting by excessively removed insulation on speaker wiring located at the amplifier output.  Amplifiers have 'SOME' protection circuitry, but I've never seen any amplifier that was totally foolproof, protecting against all problem usage.

Amplifiers with vacuum tube output stages are usually quite tolerant of abuse that might kill transistorized amplifiers.  Conversely, transistorized output stages are quite tolerant of abuse that might kill vacuum tube output stages.  Vacuum tube amps can be damaged by OPEN speaker connections/wiring.  But, they are immune to damage from shorts on the speaker connections/wiring.  Transistor output stages can be damaged by shorts or near shorts (including too low speaker resistances/ohms), but are immune to opens.

Vacuum tube amplifiers usually have limited protections besides the sometimes ineffective electronics circuitry protections.  Limited protections are had from a speaker output jack (especially SOME types of chassis-mounted 1/4" output jacks) that have a built-in switch, so if no plug/wire/speaker is connected, the jack ...hopefully ...does the necessary safety-shorting.  Some vacuum tube amps do NOT have that sort of jack, and thus may be highly susceptible to damage from 'speaker circuit opens'.

Some (especially musician's) vacuum tube amps include diodes at the output stage that can help prevent very high voltages from being produced in the output stage transformer if the amplifier does not have a speaker connected and if there is no operating protective short in the output jack.  The diodes method may not be 100% effective.

Transistor output stages are damaged by SHORT circuits, or, from excessively low ohms loads, such as from too many speakers or wrong speakers.  Short circuits in the speaker wiring, or a bad speaker, or bad speaker wiring of some sort, can cause transistor currents to rise spectacularly, and the output transistors will be destroyed, usually doing lots of other damage at the same time.  Transistorized amplifiers usually have, and NEED, MUCH more sophisticated protection circuitry, compared to vacuum tube amps.  A lot of such transistor protection circuitry is not fully protective.

If you wish to connect speakers in parallel, series, or have other requirements, please ASK US.


2.  Speaker Phasing...what is it?  Why is it important?  

A loudspeaker (except for some solid-state tweeters or other types) is, at its most simplified explanation, simply a coil of wire attached to the speaker cone, with that wound coil immersed in a strong magnetic field, via a narrow gap in the magnet.   You probably learned in school that there is a North and a South pole in a magnet, and you may remember other details about moving coils, moving magnets, and so on.   For our purposes here, the important thing is that in most situations (excluding some complicated Public Address or other systems such as vertically driven dual sub-woofer cabinets, or cabinets with many speakers, that could otherwise interfere with each other due to echo or signal canceling distances, etc.) ....you WANT your sound system's movable cone type speakers to ALL move in, or out, at the SAME time.  If not so connected, the usual result is a THINNESS of bass response, as well as a reduced bass output volume.  Over-all, your speaker cabinet with two or more wrongly phased speakers will sound lousy, as the speaker outputs try to cancel each other, to some degree or other.

At any one moment of time, where speakers are mono used in particular, but also as stereo connected if there is a mono signal, the following is the situation:
SOUND is air movement, so if a sound wave from one speaker is PUSH connected, and it reaches you when sound from some other speaker is a PULL connected type, the sounds can cancel, considerably or partially.   While the effective volume decreases, the worst part is that, typically, the result is lower mid-range to bottom bass.    This effect tends to 'gather' at some small distance from the speaker cabinet.   The over-all effect is much less at higher frequencies, and almost non-existent at near the high frequency limits of human hearing, because of how humans hear things.    But, the lower mid-range to bottom bass effects can be PRONOUNCED. 

It is possible for "Effects" units that are popular with musicians, to cause your sound to be exceptionally BAD, if the connections are wrong.

When a speaker is backwards (reverse) connected with regards to another speaker, we say they are "out of phase".
The effect can also be heard as a type of noise canceling.  You will always find lowered volume, 'thinness' of sound, etc. ...if the speakers are not too far distant from each other.

The electronics industry, speaker manufacturers, engineers, ETC., all 'agreed' many decades ago, that a STANDARD for speaker polarity was needed. The reason was so various manufacturer's speakers could be interchangeable for connections.

What was agreed upon was ...and I am making this simple for you ....if a low voltage battery was suddenly connected to a speaker, ....if the + terminal of the battery connects to the + terminal of the speaker (which is to be marked red if color marking is desired, otherwise it is to be marked with a + symbol, although many manufacturers do both) (for - terminal, it is black) .... then the speaker cone, at the instant of battery connection, will move OUTWARDS; that is, away from the magnet.

If the battery is connected backwards to properly-marked speaker terminals, then the cone moves INwards (towards/into the magnet). If one speaker moves the same for the same signal, as another speaker, they are said to be IN PHASE.  If not, they are said to be OUT OF PHASE.   Speaker phasing of separate speaker boxes, for musicians and home stereos, are designed to be IN PHASE.   For Public Address systems, it is more complicated (with many speakers in use, over distances, echoes, etc.); and there are also some types of speaker boxes that have speakers in front and rear; and they may purposely be anti-phased, usually to give increased in-phase (effectively) loudness or a thing called dampening.

The battery test is USUALLY the easiest, quickest, and most accurate method of identifying speaker terminals.  Of course, you have to be able to see the cone. Note that some speaker makers have marked their speakers, or the speaker terminals for the speaker box, or both, BACKWARDS.  JBL did this, a very long time ago.  Thus, it is a really good idea to CHECK speaker phasing, using a small battery, such as a common 9 volt type which can't deliver too much current.  A battery with a voltage under 3 volts is not likely going to move the speaker cone enough to easily see the direction it moves.  A battery should not be connected for any length of time....ONE-HALF SECOND is plenty.   You can do multiple connections, one after the other, if you need to.    Have the speaker DISCONNECTED from the amplifier for these tests.   Used properly, the method ALSO can "help" with phasing of wiring in businesses, churches, and some homes.  For large areas, and P.A. use, we can advise of the more sophisticated tests and connections that are usually needed.

One other method of checking speaker phasing is common, and is often done with Stereo-HiFi equipment, where all the terminals and connections for the speakers and/or amplifier; or, visual access to the cone ....might not be easily gotten-to ...or seen.  This method is also used with such as home theatres, with their multiple speaker systems.  This method is done with any two speakers at the same time, and repeated in all combinations of left-right-front-rear, for a home theatre.  While professionals do this with special test equipment and tones, you do not have to.   You can simply tune an FM radio (connected to the amplifier that drives the speakers) to any place BETWEEN stations, if necessary turning off any muting (sometimes selecting MONO or stereo OFF is needed).  The idea is that you will want to be listening only to HISS NOISE.  This can also be done with a common AM radio station.  Any mono, not stereo signal will work. It is easier using hiss, than program material.

Example:  Sit in a room, equal-distant from the two speakers, which are typically centered.  LISTEN, then have a friend reverse ONE ONLY speaker connection.  That is, your friend will swap + and - connections, never allowing a short circuit (for amp protection reasons).  The position of the leads will definitely cause one position of leads to be louder, than the reverse position.  If you have trouble hearing this, then, repeat, closing your eyes:   The correct position of that speaker wires is when the sound appears to come from the middle of your head, the wrong position is when you hear things separately in your individual ears.  If more than one speaker, use ONE as the master, for each test. ((For large public address systems, the testing is done and adjusted, for echo effects minimalization)).

In the same way that phasing of speakers is important, so are the connections to such as stereo phonograph/turntable cartridges, and for the SAME reasons.  Thus, almost all signal wiring has standardized color coding.  What is of much lesser importance is the LEFT-RIGHT connections for amplifiers and speakers ....except for home theatre ...and where absolute authenticity of listening position is usually desirable.

3. Amplifier biasing.   Both far too much, and too little, is discussed about amplifier biasing ...and, for tube selection and biasing:

In 90% of instances 'the talk' is about vacuum-tube biasing for musician's amplifiers.  For transistorized output stages, bias is set once, and then not again ....unless repairs are done.  Transistor output stages have the bias current set for a value that is high enough to eliminate distortion at very low volume levels, and low enough so that the output stage does not get excessively warm with no signal input.  Transistor output stages may have other adjustments, for such as DC output minimalization, balance, etc.  Vacuum tube output stages may have balance adjustments besides bias adjustments.

For vacuum tube output stages, the situation can be simple ...or, complicated.  One type of design circuit uses "cathode biasing" that  usually have no adjustments for bias.  That type of circuit is used almost exclusively for lower wattage amplifiers, with some notable exceptions.  For high output vacuum tube output stage amplifiers, the type of biasing usually used is called fixed bias, and the negative needed voltage is supplied by a negative power supply output.  Fhe bias on the output tubes is nearly always adjustable and there is no cathode resistor (or, the one used is very low in ohms, and exists primarily to allow voltage measurements across it).  Some of these amplifiers have balance adjustments, and some old amplifiers from the sixties (such as from Fender Musical Instruments Corp.) are designed to incorporate a sort of balance and bias adjustment via just one control.   Depending on the amplifier design, there may be connection places for a meter, which may be on the chassis available to the owner/user ....or, inside, and several types of adjustments. Some have lamps to indicate proper adjustments.   Adjustments allow for bias amount, balance between the tubes, etc.   Standard settings are usually specified by the manufacturer, usually an oscilloscope and a sine wave oscillator is need and one or two of the adjustments are made at or quite near-to, maximum clean signal output....this means that the output is watched on the oscilloscope, while adjustments are made.  A special resistor load is used in place of a speaker.   Transistor power stages have the bias set at certain published values.  The adjustment is usualy made for a minimum amount of current flow that sill minimizes distortion.   Note the difference, in that transistor power stage bias is usually set at very low signal output, while tubes bias is usually set for just before any more volume creates an overload while looking at the waveform on an oscilloscope (I do transistor stages on a 'scope, too).

When talk is about 'higher bias', that usually means LOWER negative bias VOLTAGE than normal or optimal, and it can result in a lowering of tube life, due to the higher continuous current flow, with little extra power output being available from the higher bias.  So, the result of so-called higher-bias is higher current through the tubes, even with with no or very little signal being present.  The manufacturer selects bias for a certain amount which relates to a certain current flow; or, more often, selects the bias so that with whatever particular tubes are installed, the tubes are operated under conditions that reduce output distortion, yet provide a good compromise for maximum power output.  USUALLY, the important biasing for vacuum tubes is set with near maximum power output, so that at overload conditions, the sound is a type of 'clean' tube amplifier overload, and not a raspy lousy sound.  Sometimes the biasing checks are done at both high output & low output.  Amplifiers for musicians are OFTEN designed so that the amplifier has one or more 'clean' pre-amplifier channels, and also one or more 'dirty' or purposely distorted channels that have the capability of front panel adjustments for such as distortion/type/etc, etc.   There may be both a master volume control and channel amplifier volume controls, and proper use will produce clean sound somewhat into the OUTPUT STAGE OVERLOAD POINT ...OR, the master volume can be turned down some, and the pre-amplifier gain control turned up, which will cause, on purpose, a hard overload sound (more or less).  Some musicians amplifiers have all sorts of combinations of these sorts of things, even multiple IN SERIES pre-amplifiers.  Some later large Marshall amps are like that.

Some amplifiers have switches that change bias for different types of sound.   There may be switches for maximum power output adjustment, or, for Triode sound, etc. Some amplifiers have front panel controls for a dozen or so different type of main amplifier sound/tone.   There is a UK/England "British" sound, and many others, some called by the particular type of circuit design, or even by vacuum tube number.   Example:  EL84 or EL34 or 6L6 sound....etc.   Some settings have other descriptive names.  Some available switch settings may modify the bias.

The TONAL QUALITY of the amplifier will change with a change of vacuum tubes and bias setting.  In many instances, amplifiers are designed to be used with more than one type of output tube, to get the 'British sound', ETC.  Marshall is relatively famous for building amplifiers that will accept several types of output vacuum tubes, fitting into the same octal socket with the same wiring....and the only change needed is a bias adjustment, by control setting ...or resistor change, ...or both.    An amplifier using 6550, or 6L6 or 5881, or EL34 is common, with many even allowing allowing KT88 and KT66 tubes. I've even seen EL37 tubes.   In some instances, with 4 or 6 output tubes, we can advise SIMPLE, NO COST methods of getting 'your tone', such as by removing certain tubes.  Experience or consultation with an audio repairman who knows his stuff, is advisable.

In some instances, a tone more to your liking is available on amplifiers with HI/LOW switches, and/or with so-called MODELING amplifiers. 

I won't get into this in much more depth, just to say that we won't usually 'over bias' your amplifiers, even if requested, unless there are special circumstances.  Large amounts of over-biasing will reduce tube life, and, in some instances, can lead to $$$ repairs.

4.  WHY do I advise as 'important', the specific order of use for your musician's amplifier's power and standby switches?

Many, not all, musician's amplifiers have both a power switch and a standby switch.  The standby switch turns off the high voltage to the output tubes.  It's really a good idea to have both of these switches.    These switches extend your output tube's life for two reasons:


While this description/advice applies to most vacuum tubes, it is more important for the large audio power output tubes for technical reasons.  At the very center of most power-type vacuum tubes is a central tube, usually round, but sometimes flattened in shape.  The central tube contains a spiral (or up and down) tungsten thread or ribbon that is heated to glowing reddish-orangish-hot, which heats the surrounding central tube to approximately the same color.   The outside of this central tube is coated with a substance that likes to emit electrons when hot, if proper voltages are applied to other elements in the vacuum tube.  The electrons can be thought of as flowing towards the big grayish surrounding metal plate structure.   If you turn ON the power and the standby (high voltage) switch at the same time, or the standby switch is turned on much too soon, then the high voltage that appears usually instantaneously on these tubes at main power turn-on with Standby in PLAY (on)  position, will 'suck' electrons from anyplace it can.  While a large current flow can damage fine-wire structures inside the vacuum tube, the discussion here is for the electrons-emitting central tube inside the vacuum tube.  If you do not have a standby switch, then the effect happens at every turn-on, and there is some effect, although much less, during turn-off.

During the time that the central tube is still slowly heating-up, the 'sucking' (sorry!) will try to find microscopic faults in the central tube coating, as the major portion of the coating is not yet hot enough for mass electron flow from every part of the surface.  So, fairly substantial current flow will be comparatively had from very tiny micro-size-pinpoints.  These pinpoints, which are otherwise generally OK faults, can not 100.00% handle the comparatively large electron flow that occurs from such a tiny area, so the tiny pinprick sized area gets too hot...that is, the outer bonded material will have VERY high heating, at microscope points.  This is akin to electric wiring with too high a current for the size of the copper wire.   In the vacuum tube under discussion here, otherwise OK faults will be made larger and coating material will likely eventually begin to flake off.  Damage can occur from short circuits by this flaking material if the flakes are large enough, and it CAN happen on vacuum tubes that are either mounted with the top of the glass UPwards........or; DOWNwards.  Damage can also come from warping of the central tube and other structures in the vacuum tube.

The short circuits can ruin the tube, smoke resistors, damage power supply diodes, and do other damage.  If you are using an oversize fuse, a huge amount of damage is possible.  NOTE that the effect can also happen (vastly less though) when turning the amplifier switches OFF in the wrong order.

The correct use of the two switches is:

A. To turn the amplifier ON, first be sure the STANDBY switch is OFF (the position for NO SOUND).  This may be confusing to you, as some amplifiers have the standby switch position for OFF, called Standby-ON.   Re-stated:  The true OFF position is the one such that the amplifier would not produce speaker output.
B.  Turn the MAINS or A.C. Power Switch to the ON position.
C.  Wait at least 30 seconds...I prefer 1 minute ....before turning the standby switch to the ON, or play, or, let's just say the functional position.
D.  It is perfectly OK, when on a gig, to turn the standby switch OFF, between sets, etc., leaving the mains power switch ON, if you wish.
Ask me about the finger-tapping test for tubes for oncoming problems.

When turning the amplifier completely OFF:
A.  Turn the standby switch to the non-function, or OFF position.
B.  After about 15 seconds, turn the mains power switch off.

5.  Why is using an oversize fuse so bad for your equipment, and when is 'wrong', actually usably OK? :

Fuses are incorporated for more than one purpose.  PRIMARILY, fuses are incorporated to prevent fires; and, to protect the circuits and components from serious, or excessively serious damage.

Fuses are rated for maximum safe voltage to be applied ....otherwise, a very damaging ARC of current might occur, for instance if you use a 25 volt rated CAR fuse, and not a proper 125 or 250 volt rated fuse.  The wrong voltage rating fuse is, however, very rarely going to be a problem.

Using a SLOW-BLOW fuse is a bit more of a problem, if the equipment was not designed for a slow-blowing fuse.  However, in many instances, one can substitute a slo-blow fuse of LOWER than equipment manufacturer standard no-blow specified current, but you need to consult with your electronics advisor (our advice is FREE).  DO NOT substitute a slow blow fuse of higher current value unless I have approved this, specifically for your particular unit.

The most common problem or potential problem that I see ....is using a fuse of higher amperage rating than the equipment is designed-for (some few amplifiers, including many tube type Marshall's, have a panel specification for amperes that IS OK to exceed a bit, so ask me).

I will try to give you a simplified explanation of why generally using an oversize ampere rating for the fuse can be so very damaging to your wallet, and thereby good for my business:

There are laws of physics involved in electricity.  You have heard of ohms, amperes (amps) and volts (voltage). There are very specific mathematical relationships between these things. A practical example might be that a piece of equipment is rated for a 2 ampere fuse.  You are on a gig, the fuse blows, and you install a 3 ampere fuse.  The fault that occurred, perhaps a tube shorted, whatever, would normally be inexpensive to repair, just replace it, and the fuse, and rarely some resistor or diode failure which is cheap.  Replacing the original 2 ampere fuse with a similar fuse might have led to a quite modest repair to even no repair beyond the cost of the fuse and maybe a shorted tube.  In fact, in some instances of the flaking problem mentioned earlier, a bit of finger tapping on the tube might let it operate a lot more before replacement.  The 3 ampere fuse MIGHT lead to a rather more expensive repair, especially if more than 3 amperes.  A substantial increase in fuse size CAN be much worse.  WHY?

ONE of the specifications of the power that can pass through a fused circuit before the fuse opens is a function of the SQUARE of the fuse current rating.  Thus, the 2 ampere fuse can pass 4 units of heating power, or however you would like to think about it.   BUT, the 3 ampere fuse will be able to pass 9 units of power.  If you installed a fuse of twice the original specification, that is, a 4 amp rated fuse, now 16 units of power can be passed.  I have ... many times ... seen 20 and 30 ampere car fuses (or, metal foil) installed in equipment.  The damage done causes the owner to bring the gear to my shop.  It often is messy, burned-up, and sometimes quite expensive to repair.

If you have to substitute a fuse, and cannot immediately get the correct one, no damage is likely to happen if you use a LOWER value fuse.  If using a larger ampere fuse, bad expensive things might happen.  It is mixed, however, in what may happen, if using a slo-blow fuse where only a standard-blow was specified.   Some amplifiers rated for standard (fast) blow fuses will be OK with a slo-blow fuse.  NOT ALL.    BUT.....it is nearly always OK to substitute a same value fast blow for a specified slo-blow .....although the fuse may blow irregularly ...even with nothing wrong with the tubes.

You can USUALLY substitute a regular fast-blow rated fuse for the slow-blow type of fuse, at the same, or SLIGHTLY increased amperage rating.

6.  Think those old NOS (new old stock) foreign vacuum tubes are way better than modern manufacture tubes??
Think those tubes are always worth the big bucks; when you can find them?
>>>...here's just one trade-secret that the tube manufacturer's don't ever want to admit to, and very few users know about, a phenomena called Heater Flash or Filament Flash (have been other words too).    NOTE that this problem is NOT common to USA-built vacuum tubes, as the manufacturing process is usually different.    While this problem is fairly common to NOS tubes like the ECC81, ECC82, ECC83, it has been seen in all sorts of vacuum tubes ...especially the small glass tubes, but even some power tubes have exhibited the problem.   First, I will discuss what it LOOKS like....because, yes, this very simple test WILL tell you if your vacuum tube has the problem, with just a LOOK at the tube when turning on the equipment:

When you first turn the power ON, power is instantly sent to the vacuum tubes to heat the filament (or, heater element part of the vacuum tube).  It is that part of the tube that, within a minute or less, turns orangey-red in color.  NOTE that if you have a separate Standby switch, it can remain in the standby off position, because having the high voltage turned ON has nothing to do with this problem I am trying to explain.

WATCH the tube AS you turn on the mains power switch.  If the filament/heater shows a very sudden flash of light, almost always this is at the bottom area of the glass envelope, then that tube HAS the problem, and is likely to soon do what we call 'burn out', but is really just the filament/heater breaking its wire.   It is this problem that causes such a short life, in what is otherwise is usually a really nicely made, low-noise, well-performing, foreign-made, OLD STOCK, vacuum tube.

If you have a choice, use a tube tester, or the amp or other piece of equipment the tube will be used in, as a test instrument...to power-up that tube BEFORE you purchase it.  REJECT such tubes unless you understand the life problem and can deal with it.  Sometimes, in the dual-triode tubes mentioned, only one of the filaments/heaters will exhibit the problem.  REJECT!

Note, that if you had a way to SLOWLY power the tube filaments/heaters, the problem would not exist.  Circuits and methods have been designed to do that.  After all, some of those foreign tubes are otherwise very well made. The method I have installed in units, and that I recommend, is simple.  You add a filament switch, and put a resistor across it, and wire that assembly in series with one of the filament connections.  I prefer to do this, when it's electrically possible, so that all the tubes in a unit are being fed filament/heater voltage, via this switch. The value of the resistor depends on the total tubes filament current.  When you power up the unit, filament/heater switch OFF, the resistor allows only a modest amount of current to flow.  After maybe a minute, turn the switch ON.   If you have a standby switch, THEN is the time to set it to the operating position. There are some very $$$ vacuum tubes that have this problem, and sometimes, after informing the customer of the problem, the request will be for even more reliability, and I use a three way switch.  This is almost never done for anything but certain very expensive tubes used in industrial or commercial equipment.  No, a three way switch is not needed for EL37 audio tubes.  Said another way, on some vacuum tubes designs, and this does not necessarily mean all tubes of a same number, it is the first fraction of a second at 'lighting up'; power on, ...that causes fast wear on the tube filament connections.

 



Future articles/item to discuss are being considered.....(let's have your ideas/input):


7.  Effects of removing half of the output tubes from a 4 or 6 output tube amplifier.
8.  Substituting amongst 12AX7, 12AU7, 12AT7, ETC.   AND, what about ECC81, ECC82, ECC83...etc?
Is there a REAL difference in sound quality/tone, between various tubes, both original numbers and substitutes?
What's the truth about NOS tubes?
9.  Setting basic bias yourself.... how-to, pitfalls, etc.
10.  How to wire speakers and match them to amplifiers. Series connections, parallel connections, combinations.  Effective ohms loads.  Effects of speaker impedances (ohms) on amplifier distortion.

 

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