Fender deLuxe Hot Rod ,2002

[N Cook]

B+ is a class of supply, B is high voltage, and + indicates it is
negative ground, so all readings will be positive. Individual supplies
may be labeled: 'Second anode', 'High voltage', 'Focus'. It depends on
the item. You see transmitters with thousands of volts, at high
current. Before the metering it is still B+, and after may be called
the plate supply, or plate voltage.

You need to download the scan of Radiotron Designers Handbook (4th
edition)

http://www.pmillett.com/Books/intro_RDH4.pdf is one source. This is a
25 MB download, but has more about Vacuum tubes than any other book you
will likely find in a single book than any other.

http://www.pmillett.com/ has other books on tubes, as well.


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So you don't have a generic equivalent for the term EHT which could be any
voltage, from anywhere, for any purpose, anywhere between say 1 and 50 KV ?

 

[N Cook]

Well, not if you work on this stuff a lot, and have at least a basic
understanding of the 'musicality' of particular guitar / amplifier
combinations. If you hear a cheapo 'starter' guitar, played through a fully
solid state amplifier more suited to vocals, or a keyboard, then listen to
say a Fender / Fender combination, you'd know what I mean. I suspect that
most on here who do this work seriously, know exactly what I'm saying.


Despite what some on here would sometimes have you believe, occasionally, it
*is* just subjective. I would actually think that it would be pretty
difficult to analyse the difference to the point of being able to
demonstrate it, technically. By suggesting that this was 'not your thing', I
intended no offence to your abilities. I know many engineers that are very
good in many fields, but not in the repair of valve amps. I am sure that
there are others out there who, unlike me, are properly musical, that have a
far better ear for problems than I do.

As an example, a few months back, I had a valve band amp in that just
'didn't sound right'. The owner said that it was quiet, and sounded 'thin'.
It wasn't actually all that quiet, but maybe a little compared to what he
was used to. 'Thin' was a good description of the sound. You couldn't really
say that it lacked in bass, or any other register really. It just sounded,
well thin ! With a sine wave and a 'scope and a power load and meter, there
was barely anything amiss with the output waveform or power level. The one
thing that did show on the 'scope, was a slight asymmetry to the wave, but
it was slight, and could have easily been missed. The problem turned out to
be the screen feed resistor on one of the output valves (just a 2 rather
than a 4 valve lineup). It was completely open, so there was no screen
voltage on that valve at all, which would have meant that it was barely
working, so you might have expected to have seen a much more distorted
waveform at the output, as you would have with a semiconductor amp.

When the resistor was replaced, and that valve's contribution to the output
stage was restored, there was little difference in either the overall sine
output power, or the waveshape, but the sound was now much better than
before. It now sounded 'right'. Now I know that doesn't explain the
mechanism of why or just how it sounded 'thin' before, and 'round' after,
but as an engineer doing a lot of this stuff, I knew that it was now
repaired, and the owner agreed. He made a point of calling the shop, and
telling them how 'good' (there we go again ...!) it sounded compared to how
it had for some time. So I make no excuse for using phrases on here like
that I used with the Fender ...

Arfa

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 ?

 

[Gareth Magennis]

Left to me I would have been perfectly happy leaving valve stuff back in
the
fifties and earlier.
But these musicians and HiFi nuts will keep buying the stuff and then
expect
people to repair mid 20th century technology that is unbelievably still
being made in the 21st C.

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.

 

[N Cook]

N Cook wrote:




+HV

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

Michael

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

 

[msg]

N Cook wrote:

What do you call the seriously high PDA (post deflection acceleration
voltage) in an oscilloscope or TV, surely something other than B+ ?

+HV

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

Michael

 

[msg]

Arfa Daily wrote:

As an example, a few months back, I had a valve band amp in that just
'didn't sound right'. The owner said that it was quiet, and sounded 'thin'.
It wasn't actually all that quiet, but maybe a little compared to what he
was used to. 'Thin' was a good description of the sound. You couldn't really
say that it lacked in bass, or any other register really. It just sounded,
well thin ! With a sine wave and a 'scope and a power load and meter, there
was barely anything amiss with the output waveform or power level.

<snip>

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

 

[Arfa Daily]

So what did this faullt look like graphically on a scope ?

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.

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 ?

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

 

[Arfa Daily]

Arfa Daily wrote:



<snip>

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 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

 

[Ron(UK)]

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 ?

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)

 

[James Sweet]

What is the US term for EHT (Extra High Tension) , say more than 1KV ?

B++ ?

HV

 

[James Sweet]

What do you call the seriously high PDA (post deflection acceleration
voltage) in an oscilloscope or TV, surely something other than B+ ?

HV or 2nd Anode.

 

[Meat Plow]

Well, not if you work on this stuff a lot, and have at least a basic
understanding of the 'musicality' of particular guitar / amplifier
combinations. If you hear a cheapo 'starter' guitar, played through a
fully solid state amplifier more suited to vocals, or a keyboard, then
listen to say a Fender / Fender combination, you'd know what I mean. I
suspect that most on here who do this work seriously, know exactly what
I'm saying.

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

 

[Meat Plow]

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 ?

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

 

[Michael A. Terrell]

As your description continues, you have found an open screen resistor.
Proper instrumentation certainly would have disclosed changes in distortion
and spectral response.

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.


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[Michael A. Terrell]

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

No. You will see the approximate voltage labeled, like "CAUTION
25,000 VOLTS"


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[Ron(UK)]

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)

 

[Ron(UK)]

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).

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)

 

[msg]

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

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

 

[msg]

<snip>

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.

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

 

[Mr. Land]

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.

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