Fender deLuxe Hot Rod ,2002

fully

be

work

it

I a

'thin'.

really

there

to

output

how

So what did this faullt look like graphically on a scope ? Terms like 'thin' and 'round' may mean something to some musos but they mean absolutely nothing to me. How am I suppose to know whether that is how another muso prefers his amp to distort, that way, in normal use ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

What sort of attitude is that? These people are expecting that the person they take their broken equipment to and pay them to repair it, is going to be competent enough to do so. If you have so little knowledge and such disdain for valve amplifiers and the people that use them, then why do you attempt these repairs? There are valve techs out there who have pride and enthuiasm and a great deal of knowledge and respect for their customers, it would perhaps be better to refer these repairs on to one of them.

Gareth.

So generically, HV for say anything in region of about 100 to 900V and +HV for 1KV upwards ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

+HV

Note that actual voltage value will likely be appended to any designation along with ! and other ISO warning symbols.

Michael

As your description continues, you have found an open screen resistor. Proper instrumentation certainly would have disclosed changes in distortion and spectral response. I agree that the subjective sound of amp/instrument combinations encompasses an 'art', but it certainly can be quantified, and likely should be for purposes of future development (and I am sure that instrument and amp makers have copious amounts of data that document theirs and their competitors products).

Michael

I thought that I explained that above ... With a sine wave going in, the output waveform, viewed on a 'scope, was very slightly asymmetric. That is, one half of the wave was not quite as big as the other, and when looked at

*very* carefully, it was not quite 'sine shaped'. I can't say any more than that. That's how it was.

Well, if the terms 'thin' and 'round' have no 'amplifier sound' meaning to you, then maybe band equipment repairs are not the right thing for you. Recognising 'good' distortion, and 'bad' distortion, is fundamental to the process of understanding this gear. Trust me, the 'thin' sound that this amp produced, would not have been a type of distortion that any guitar player would have found desirable. Whilst the sound was not hugely bad, I think that anyone with a basic 'ear' would have immediately said that it didn't sound 'right'. Again, there's little more that I can say about it. That's the way it was. It sounded 'thin' and I'm pretty sure that others on here know exactly what I mean by that. Anyone care to comment ?

Arfa

Maybe you could classify it as 'intune' distortion (harmonious) and out of tune distorion (dischordant) It`s all to do with the harmonics produced when the signal breaks up - even and odd harmonics.

A really great guitar amplifier is alive, it has balls, it feels willing to work. It`s responsive and eager, raring to go, the sound jumps out and the tone comes naturally, it breathes with the player. The distortion slides in rich and creamy, it soars at the top and growls at the bottom. It makes playing a real pleasure and easy.

A poor amplifier does none of these things and makes playing unrewarding and dificult if you have to wring the tone out of the amp.

Of course it`s not just the amplifier which creates the sound, the speaker itself adds to the distortion - those concentric ridges on the cone of a guitar speaker help to make the speaker 'trash out' at lower volumes, and the guitar itself will have a distinctive tone. There`s a wide variation in the output levels of various brands of guitar pickup. Also the way an instrument is played makes a difference, a heavy handed player will get a more strident heavy tone than a delicate picker.

All these variants work together in producing an individuals tone

Needless to say, an amplifier which gives you a near perfect reproduction of the input signal isnt what guitarists are looking for.

You can change the sound of a valve amplifier a great deal just by adjusting the bias a tiny amount, this may show up only minimally on a scope trace.

all IMHO of course

Ron(UK)

I take your point, and I'm sure that with a spectrum analyser on the end, the problem probably *could* have been quantified, but that is not really what the repair business is about. Whilst knowing the exact mechanism of why a fault presents in the way it does, is of academic interest, the key to making a living at repairing, is to get items on and off the bench as quickly as possible, and for the most part, that precludes carrying out detailed analyses of problems, for the interest of why the sound is as it is. In the case I cited, there was a clear problem, which I was able to recognise using my mark one ear. A generator and 'scope combination, which is a fundamental repair bench test gear set up, always on, always ready to roll, failed to show any clear reason for the odd sound. A check of the voltages around the output stage was indicated, to get an idea of how the bias looked between the two valves. This quickly revealed the missing screen voltage at the botom end of the feed resistor. An ohms check across the resistor revealed it to be open, and a further check to deck proved that a short circuit decoupling cap, was not the cause. Replacing the resistor fixed it. Total time from start to finish, under a half hour. Profit made.

The point I am making, is that for most practical purposes when trying to make a living repairing this stuff, a deep knowledge of the kit and what it

*should* sound like, scores over applying fancy test gear, every time. If you need to resort to the use of such items as spectrum analysers to get to the bottom of faults like open screen resistors, then you are never going to make a living doing this sort of repair.

Arfa

HV

HV or 2nd Anode.

Not to mention those of us that along with servicing both amps and guitars, play Fender Strats through Fender Twins. :)

Takes experience and the willingness to learn how to do it right neither of which you seem particularly interested in.

I've found plenty of problems with nothing more than a voltmeter, and knowledge of tube circuits. A 'RCA Receiving Tube Handbook' was carried in one of the tube caddies, in case there was no schematic available.

The scope will narrow it to a stage faster, if it's already on, and at the bench, but a lot of repairs were in the field, and were emergency repairs.

--
aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

http://improve-usenet.org/index.html

No. You will see the approximate voltage labeled, like "CAUTION

25,000 VOLTS"

--
aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

http://improve-usenet.org/index.html

To Mr Cook

I suggest you get hold of a copy of R Aspen Pitmann`s book The Tube Amp book. Not only does it have a lot of explanetary theoretical stuff without going too deep, it also has sections on tube characteristics and biasing, and a large selection on troubleshooting and modifications. I understand the latest version also includes two cd roms of circuit diagrams.

Ron(UK)

you could perhaps form hard data for a given amplifier alone, but as I pointed out earlier, the total sound relies on other factors, the speakers, the output impedance, the load the speakers place on the amplifier, all are dificult to quantify. even diferent makes of output and preamplifier valves have their own distinctive sound - even valves from the same maker can be graded into batches which sound diferently to other batches.

A valve amplifier is a far more organic beast than a solid state device.

Ron(UK)

Sorry, I should have written +/-HV depending on polarity. I guess HV is anything the labeler determines to be 'high voltage' in whatever context it appears. I would suggest 1KV and up is common.

Michael

Agreed. My comments were directed at what appeared to be an assertion in other posts that the musicality of an instrument/amp combination couldn't be measured but only 'understood' or 'perceived' by a musician or other skilled artisan. I would suggest that somewhere there is hard data for this sort of thing (not readily available to the public or repair centers).

Michael

is,

at

han

to

he

amp

r t s e

Um, which one is this??? I want to get one....