Hmm!

Hmm!

I wonder what the DC resistance of a 250mA fuse might
be?

I have just been speaking with a guy would told me that he
has replaced the fuse from the CT of the OPT of his tube
amp with a wire link, "because the fuse adds to the power
supply impedance and does not have a linear response"

He could not quote any reference to substantiate this.

I wonder what the audio bandwidth impedance of a
250mA fuse might be? -)

Compared to the cost of an OPT, the fuse seems to be a
good component for such a small investment.

Iain

Re: Hmm!


"Iain Churches" <IainNG@kolumbus.fi> wrote in message
news:Q9EQj.342739$147.94179@reader1.news.saunalahti.fi...
>I wonder what the DC resistance of a 250mA fuse might
> be?
>
> I have just been speaking with a guy would told me that he
> has replaced the fuse from the CT of the OPT of his tube
> amp with a wire link, "because the fuse adds to the power
> supply impedance and does not have a linear response"
>
> He could not quote any reference to substantiate this.
>
> I wonder what the audio bandwidth impedance of a
> 250mA fuse might be? -)
>
> Compared to the cost of an OPT, the fuse seems to be a
> good component for such a small investment.
>
> Iain
>
Hi Ian:

Here's the Littelfuse data for a standard 3AG type fast blow 250mA fuse.
The cold DCR is 2 ohms.

* w w w .littelfuse . com /data/en/Data_Sheets/312_318.pdf

I know that the DCR of these things does change over a cycle, the amount of
change being dependent on issues that determine fuse heating such as:

1) Ambient temperature.
2) Air flow over fuse.
3) How close to the fuse rating is the rms current you're passing through
it.
4) Current waveform.

I have never seen any numbers (that looked to be from a reliable source)
showing the magnitudes of the DCR change.

I always include fuses (of about 250mA) in the CT of the output transformers
of my own amplifiers.

There's an easy way to either put the boots to or substantiate this as a
problem. Find someone with an Audio Precision System 2 with DSP option
(there is a newer model available now...see Audio Precision site) and simply
do a THD test with and without the fuse. When you look at the spectrum that
the AP has plotted, you will see immediately if this issue is fact or fable.

One of the few (and believe me, they're aren't too many) things I miss now
that I am retired, is not having access to an Audio Precision any longer.

Best Regards : Doug Bannard

Re: Hmm!



"Doug Bannard" <ve3spf@rogers . com > wrote in message
news:Sf-dnZWbQ9c3s47VnZ2dnUVZ_ommnZ2d@supernews . com ...
>
> "Iain Churches" <IainNG@kolumbus.fi> wrote in message
> news:Q9EQj.342739$147.94179@reader1.news.saunalahti.fi...
>>I wonder what the DC resistance of a 250mA fuse might
>> be?
>>
>> I have just been speaking with a guy would told me that he
>> has replaced the fuse from the CT of the OPT of his tube
>> amp with a wire link, "because the fuse adds to the power
>> supply impedance and does not have a linear response"
>>
>> He could not quote any reference to substantiate this.
>>
>> I wonder what the audio bandwidth impedance of a
>> 250mA fuse might be? -)
>>
>> Compared to the cost of an OPT, the fuse seems to be a
>> good component for such a small investment.
>>

> Here's the Littelfuse data for a standard 3AG type fast blow 250mA fuse.
> The cold DCR is 2 ohms.
>
> * w w w .littelfuse . com /data/en/Data_Sheets/312_318.pdf
>
> I know that the DCR of these things does change over a cycle, the amount
> of change being dependent on issues that determine fuse heating such as:
>
> 1) Ambient temperature.
> 2) Air flow over fuse.
> 3) How close to the fuse rating is the rms current you're passing through
> it.
> 4) Current waveform.
>
> I have never seen any numbers (that looked to be from a reliable source)
> showing the magnitudes of the DCR change.
>
> I always include fuses (of about 250mA) in the CT of the output
> transformers of my own amplifiers.

Hi Doug.

It seems to me to be such a good idea, that I wondered
why it is not more common. If an output tube shorts, then the
replacement of that tube and the fuse is a much more palatable
proposition than the replacement of both tube and OPT

>
> There's an easy way to either put the boots to or substantiate this as a
> problem. Find someone with an Audio Precision System 2 with DSP option
> (there is a newer model available now...see Audio Precision site) and
> simply do a THD test with and without the fuse. When you look at the
> spectrum that the AP has plotted, you will see immediately if this issue
> is fact or fable.

I have a HP distortion analyzer, so I could plot distortion across the audio
bandwidth at various power levels with the fuse or with a link in its place.

But then again, this is one of those inexplicable "audiophile" things:-)
People can hear things than none of the rest of us can measure!


Regards
Iain

Re: Hmm!

"Iain Churches" <IainNG@kolumbus.fi> wrote in message
news:Q9EQj.342739$147.94179@reader1.news.saunalahti.fi

> I wonder what the DC resistance of a 250mA fuse might
> be?

Maybe an ohm or two, depending on rated thermal delay, etc.

For the details, check a fuse manufacter's web sie for a data sheet, for
example:

* w w w .littelfuse . com /searchresults.html?No=20&RT=Part&NN=0%3aTechnology%3a158%3b0%3aIsObsolete%3a262%3b0%3aNon_Euro_Part%3a263%3b0%3aOpening_Characteristic%3a4294966626


> I have just been speaking with a guy would told me that he
> has replaced the fuse from the CT of the OPT of his tube
> amp with a wire link, "because the fuse adds to the power
> supply impedance

Yes, but probably not signficantly.

> and does not have a linear response"

Fuses elements are bulk metal and are therefore linear, given that their
temperature is not varying.

However, the temperature of a fuse element is varying pretty strongly with
some time lag, depending on the current flow.

If you apply a sinusoidal time-varying current to a fuse, there will be a
fairly linar voltage across the fuse, particularly at low frequencies. This
is a well-known problem with loudspeaker fuses. It is better to fuse the
drivers each with their own fuse to avoid modulation of high frequencies by
low frequencies. Of course, the tweeter voice coil will be doing this, as
well.

> He could not quote any reference to substantiate this.

Greiner contributed an article to the JAES in the 70s or 80s that covered
the effects of fuse resistance on loudspeakers and included distortion
measurements.

> I wonder what the audio bandwidth impedance of a
> 250mA fuse might be? -)


No joke, the fuses resistance will be varying when passing a strong low
frequency tone.

> Compared to the cost of an OPT, the fuse seems to be a
> good component for such a small investment.

Given how much nonlinear distoriton tubed amps have at low frequencies,
fuses are probably not a serious problem. If you really want to protect a
power amp without side-effects, you'll probably use other means.

Re: Hmm!


>
> > I wonder what the DC resistance of a 250mA fuse might
> > be?
>
> Maybe an ohm or two, depending on rated thermal delay, etc.
>
> For the details, check a fuse manufacter's web sie for a data sheet, for
> example:
>
> * w w w .littelfuse . com /searchresults.html?No &RT=Part&NN=0%3aTec...


Rather than wondering, measuring might work better.

Nevertheless, the high voltage low current paradigm of the tube
amplifier makes this resistance pretty irrelevant. That's the appeal
of tubes: insulation is cheaper than copper and moreover one needn't
be as obsessed with current paths.

>
> > I have just been speaking with a guy would told me that he
> > has replaced the fuse from the CT of the OPT of his tube
> > amp with a wire link, "because the fuse adds to the power
> > supply impedance
>
> Yes, but probably not signficantly.
>
> > and does not have a linear response"
>
> Fuses elements are bulk metal and are therefore linear, given that their
> temperature is not varying.
>
> However, the temperature of a fuse element is varying pretty strongly with
> some time lag, depending on the current flow.


> > I wonder what the audio bandwidth impedance of a
> > 250mA fuse might be? -)
>
> No joke, the fuses resistance will be varying when passing a strong low
> frequency tone.
>
> > Compared to the cost of an OPT, the fuse seems to be a
> > good component for such a small investment.
>
> Given how much nonlinear distortion tubed amps have at low frequencies,
> fuses are probably not a serious problem. If you really want to protect a
> power amp without side-effects, you'll probably use other means.

Fuses used properly are not a serious problem, and neither is the
distortion good tube amps make at low frequencies.

> When you say active protection are you alluding to a current crowbar
circuit?

Often although that isn't the best way to go in most cases. One of
the best protections for tube output stages is a fuse resistor in the
cathode circuit. In fixed bias amplifiers they serve two functions:
they meter quiescent standing current and open if the bias or a tube
fails.

Re: Hmm!



Iain Churches wrote:
>
> I wonder what the DC resistance of a 250mA fuse might
> be?
>
> I have just been speaking with a guy would told me that he
> has replaced the fuse from the CT of the OPT of his tube
> amp with a wire link, "because the fuse adds to the power
> supply impedance and does not have a linear response"
>
> He could not quote any reference to substantiate this.
>
> I wonder what the audio bandwidth impedance of a
> 250mA fuse might be? -)
>
> Compared to the cost of an OPT, the fuse seems to be a
> good component for such a small investment.
>
> Iain

Fuses between the B+ and a CT on an OPT are not a bad idea.
90% of music from tube amps is from PP,
and while the amp remains fully in class A.
So the non-linarity of the fuse impedance is utterly negligible.

Traditionally, ppl said fuses before speakers were bad because there the
fuse value
might be 4 amps, and the distortions caused by the fuse could be greater
than the those from the amp,
which might only measure 0.001% at a watt or two which is all most ppl
ever use.
A 4A fuse may have 0.01% thd, 10 times more. It doesn't make much
difference though eh.
A piece of small dia copper wire soldered in would be ok except that its
temp varies and hence its resistance.
Maybe not to much though.

Active protection against excessive cathode current works a lot better
though.

The problem with a fuse is at low levels when a speaker wire has frayed
strands causing a short
that isn't noticed, and load becomes less than 0.3 ohms, so the output
tubes or tyransistors cook themselves
even at low levels even though there isn't enough current to blow a
fuse.

Active protection is better.

Patrick Turner.



Patrick Turner.

Re: Hmm!


"Patrick Turner" <info@turneraudio . com .au> wrote in message
news:481352EF.E36EF12D@turneraudio . com .au...
>
>
> Iain Churches wrote:
> >
> > I wonder what the DC resistance of a 250mA fuse might
> > be?
> >
> > I have just been speaking with a guy would told me that he
> > has replaced the fuse from the CT of the OPT of his tube
> > amp with a wire link, "because the fuse adds to the power
> > supply impedance and does not have a linear response"
> >
> > He could not quote any reference to substantiate this.
> >
> > I wonder what the audio bandwidth impedance of a
> > 250mA fuse might be? -)
> >
> > Compared to the cost of an OPT, the fuse seems to be a
> > good component for such a small investment.
> >
> > Iain
>
> Fuses between the B+ and a CT on an OPT are not a bad idea.
> 90% of music from tube amps is from PP,
> and while the amp remains fully in class A.
> So the non-linarity of the fuse impedance is utterly negligible.
>
> Traditionally, ppl said fuses before speakers were bad because there the
> fuse value
> might be 4 amps, and the distortions caused by the fuse could be greater
> than the those from the amp,
> which might only measure 0.001% at a watt or two which is all most ppl
> ever use.
> A 4A fuse may have 0.01% thd, 10 times more. It doesn't make much
> difference though eh.
> A piece of small dia copper wire soldered in would be ok except that its
> temp varies and hence its resistance.
> Maybe not to much though.
>
> Active protection against excessive cathode current works a lot better
> though.
>
> The problem with a fuse is at low levels when a speaker wire has frayed
> strands causing a short
> that isn't noticed, and load becomes less than 0.3 ohms, so the output
> tubes or tyransistors cook themselves
> even at low levels even though there isn't enough current to blow a
> fuse.
>
> Active protection is better.
>
> Patrick Turner.

When you say active protection are you alluding to a current crowbar
circuit?

Cordially,
west
>
>
>
> Patrick Turner.

Re: Hmm!



West wrote:
>
> "Patrick Turner" <info@turneraudio . com .au> wrote in message
> news:481352EF.E36EF12D@turneraudio . com .au...
> >
> >
> > Iain Churches wrote:
> > >
> > > I wonder what the DC resistance of a 250mA fuse might
> > > be?
> > >
> > > I have just been speaking with a guy would told me that he
> > > has replaced the fuse from the CT of the OPT of his tube
> > > amp with a wire link, "because the fuse adds to the power
> > > supply impedance and does not have a linear response"
> > >
> > > He could not quote any reference to substantiate this.
> > >
> > > I wonder what the audio bandwidth impedance of a
> > > 250mA fuse might be? -)
> > >
> > > Compared to the cost of an OPT, the fuse seems to be a
> > > good component for such a small investment.
> > >
> > > Iain
> >
> > Fuses between the B+ and a CT on an OPT are not a bad idea.
> > 90% of music from tube amps is from PP,
> > and while the amp remains fully in class A.
> > So the non-linarity of the fuse impedance is utterly negligible.
> >
> > Traditionally, ppl said fuses before speakers were bad because there the
> > fuse value
> > might be 4 amps, and the distortions caused by the fuse could be greater
> > than the those from the amp,
> > which might only measure 0.001% at a watt or two which is all most ppl
> > ever use.
> > A 4A fuse may have 0.01% thd, 10 times more. It doesn't make much
> > difference though eh.
> > A piece of small dia copper wire soldered in would be ok except that its
> > temp varies and hence its resistance.
> > Maybe not to much though.
> >
> > Active protection against excessive cathode current works a lot better
> > though.
> >
> > The problem with a fuse is at low levels when a speaker wire has frayed
> > strands causing a short
> > that isn't noticed, and load becomes less than 0.3 ohms, so the output
> > tubes or tyransistors cook themselves
> > even at low levels even though there isn't enough current to blow a
> > fuse.
> >
> > Active protection is better.
> >
> > Patrick Turner.
>
> When you say active protection are you alluding to a current crowbar
> circuit?

In tube amps there is no need for a crowbar type circuit to force a
mains fuse to blow.

My website has schematics of a few different types of cathode dc
detectors
fitted to output tubes.
If Ik dc rises to 2 times Ik at idle for longer than 4 seconds, the amp
is turned off by a relay.

With music it will happen at low levels if there is a shorted speaker
lead or speaker.

But otherwise severe overload will trip the protection circuit.

If any one or more of the output tubes goes to being sick and conducts
too much dc, the
amp is turned off.

Patrick Turner


>
> Cordially,
> west
> >
> >
> >
> > Patrick Turner.

-- deleted messages --

-- deleted messages --

Re: Hmm!


"West" <west@verizon . net > wrote in message
news:b7URj.30218$Rk6.28029@trnddc07...
>

<snip>

>
> Talk about sound, Boss. Just what kind of Gregorian Chant juxtaposition
> (best word I can think of at this ungodly hour) with the clarinet do you
> listen to? I simply adore Gregorian Chant and I also am fond of the
> clarinet. Combining the two seems a bit off-beat and confusing, but I know
> better than to question your tastes. Will you share label(s) with me so I
> can also taste and perhaps in a way, delve into your inner sanctum?
>
> Cordially,
> west
>
>> Andre Jute
>> Visit Jute on Amps at * members.lycos.co.uk/fiultra/
>> "wonderfully well written and reasoned information
>> for the tube audio constructor"
>> John Broskie TubeCAD & GlassWare
>> "an unbelievably comprehensive web site
>> containing vital gems of wisdom"
>> Stuart Perry Hi-Fi News & Record Review
>


Andre, you are a wonderful ventriloquist, I couldn't see your lips moving at
all there.

In awe

Keith

Re: Hmm!

On Apr 30, 11:54 pm, "keithr" <kei...@nowhere . com .au> wrote:
> "West" <w...@verizon . net > wrote in message
>
> news:b7URj.30218$Rk6.28029@trnddc07...
>
>
>
>    <snip>
>
>
>
>
>
> > Talk about sound, Boss. Just what kind of Gregorian Chant juxtaposition
> > (best word I can think of at this ungodly hour) with the clarinet do you=

> > listen to? I simply adore Gregorian Chant and I also am fond of the
> > clarinet. Combining the two seems a bit off-beat and confusing, but I kn=
ow
> > better than to question your tastes. Will you share label(s) with me so =
I
> > can also taste and perhaps in a way, delve into your inner sanctum?
>
> > Cordially,
> > west
>
> >> Andre Jute
> >> Visit Jute on Amps at * members.lycos.co.uk/fiultra/
> >> "wonderfully well written and reasoned information
> >> for the tube audio constructor"
> >> John Broskie TubeCAD & GlassWare
> >> "an unbelievably comprehensive web site
> >> containing vital gems of wisdom"
> >> Stuart Perry Hi-Fi News & Record Review
>
> Andre, you are a wonderful ventriloquist, I couldn't see your lips moving =
at
> all there.
>
> In awe
>
> Keith

WTF are you going on about this time, Keefie?

Unsigned out of contempt for a fool

Re: Hmm!


"Andre Jute" <fiultra1@yahoo . com > wrote in message
news:ba9a3cb3-0413-465c-bce2-0ca6d36ce8a1@q27g2000prf.googlegroups . com ...
On Apr 30, 11:54 pm, "keithr" <kei...@nowhere . com .au> wrote:
>>
>> news:b7URj.30218$Rk6.28029@trnddc07...
>>
>> <snip>
>>>
>> > Talk about sound, Boss. Just what kind of Gregorian Chant juxtaposition
>> > (best word I can think of at this ungodly hour) with the clarinet do
>> > you
>> > listen to? I simply adore Gregorian Chant and I also am fond of the
>> > clarinet. Combining the two seems a bit off-beat and confusing, but I
>> > know
>> > better than to question your tastes. Will you share label(s) with me so
>> > I
>> > can also taste and perhaps in a way, delve into your inner sanctum?
>>
>> > Cordially,
>> > west
>>
>> >> Andre Jute
>> >> Visit Jute on Amps at * members.lycos.co.uk/fiultra/
>> >> "wonderfully well written and reasoned information
>> >> for the tube audio constructor"
>> >> John Broskie TubeCAD & GlassWare
>> >> "an unbelievably comprehensive web site
>> >> containing vital gems of wisdom"
>> >> Stuart Perry Hi-Fi News & Record Review
>>
>> Andre, you are a wonderful ventriloquist, I couldn't see your lips moving
>> at
>> all there.
>>
>> In awe
>>
>> Keith
>
> WTF are you going on about this time, Keefie?

I thought that you had aspirations to being thought of as an intellectual,
if you can't work it out then on the contrary your IQ must be room
temperature in C.

> Unsigned out of contempt for a fool

The fool being one Andre Jute

In considerably less awe

Keith

Re: Hmm!

On May 1, 6:24 am, "keithr" <kei...@nowhere . com .au> wrote:
> "Andre Jute" <fiult...@yahoo . com > wrote in message
>
> news:ba9a3cb3-0413-465c-bce2-0ca6d36ce8a1@q27g2000prf.googlegroups . com ...
> On Apr 30, 11:54 pm, "keithr" <kei...@nowhere . com .au> wrote:
>
>
>
>
>
> >>news:b7URj.30218$Rk6.28029@trnddc07...
>
> >> <snip>
>
> >> > Talk about sound, Boss. Just what kind of Gregorian Chant juxtapositi=
on
> >> > (best word I can think of at this ungodly hour) with the clarinet do
> >> > you
> >> > listen to? I simply adore Gregorian Chant and I also am fond of the
> >> > clarinet. Combining the two seems a bit off-beat and confusing, but I=

> >> > know
> >> > better than to question your tastes. Will you share label(s) with me =
so
> >> > I
> >> > can also taste and perhaps in a way, delve into your inner sanctum?
>
> >> > Cordially,
> >> > west
>
> >> >> Andre Jute
> >> >> Visit Jute on Amps at * members.lycos.co.uk/fiultra/
> >> >> "wonderfully well written and reasoned information
> >> >> for the tube audio constructor"
> >> >> John Broskie TubeCAD & GlassWare
> >> >> "an unbelievably comprehensive web site
> >> >> containing vital gems of wisdom"
> >> >> Stuart Perry Hi-Fi News & Record Review
>
> >> Andre, you are a wonderful ventriloquist, I couldn't see your lips movi=
ng
> >> at
> >> all there.
>
> >> In awe
>
> >> Keith
>
> > WTF are you going on about this time, Keefie?
>
> I thought that you had aspirations to being thought of as an intellectual,=

> if you can't work it out then on the contrary your IQ must be room
> temperature in C.
>
> > Unsigned out of contempt for a fool
>
> The fool being one Andre Jute
>
> In considerably less awe

Good. Then when can we expect you to stop trying to "prove" you're as
good as me?

Andre Jute
Thumbs well clear of the bricks

-- deleted messages --