50V , low wattage lamp (or seriesed lower V ones) (assuming normal testing
is 10 to 20W range) to visually show if the volume is set too high, also if
high level high f oscillation on the output; sacrificial, fusewise, if
overdriven.
AC voltmeter , preferably autoranging for possible overload situation, to
measure/long term monitor the RMS power.
High power speaker pot (plus droppers) leading to a low quality ,
sacrificial ( for intitial maybe problematic testing) small speaker, for
basic possible intermittant sound, on/off, indication. Can be switched out
by plugging in a good quality speaker for audio monitoring of quality of
sound issues in otherwise known good amp.
Provision for coupling in a scope for distortion monitoring, when necessary.
Any other add-ons that others know of ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N_Cook" wrote in message
...
50V , low wattage lamp (or seriesed lower V ones) (assuming normal testing
is 10 to 20W range) to visually show if the volume is set too high, also
if
high level high f oscillation on the output; sacrificial, fusewise, if
overdriven.
AC voltmeter , preferably autoranging for possible overload situation, to
measure/long term monitor the RMS power.
High power speaker pot (plus droppers) leading to a low quality ,
sacrificial ( for intitial maybe problematic testing) small speaker, for
basic possible intermittant sound, on/off, indication. Can be switched out
by plugging in a good quality speaker for audio monitoring of quality of
sound issues in otherwise known good amp.
Provision for coupling in a scope for distortion monitoring, when
necessary.
Any other add-ons that others know of ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


I also have a box I made which has a stereo input, switchable to
paralleled-channel mono, with two switchable and variable basic ranges of
zero to low, for low level instrument simulation such as guitar pickup, and
zero to high for line level tests. It also contains two 600R line
transformers to produce 'balanced' outputs for testing amps with a balanced
XLR type input. I have a special Speakon adaptor which has a built in
standard 1/4" jack so that the test speaker can have a normal jack plug on
it, and if I get an amp for repair that has Speakon outputs, as many of the
higher power heads have, it's just a case of plug in the adaptor first.

I also have a little box that I made that has a 'normal' edgewise meter, and
a centre zero edgewise meter and a 3 pin plug for setting and checking the
bias balance on Fender Twins.

My load tester has a built in very heavily attenuated 4" 'squeaker' with
volume control, for monitoring intermittent faults, and jack-switched
'through' output for a genuine speaker. It also has a crude power meter
based on measuring the voltage across the load. This stays in circuit if the
through socket is used to connect a real speaker. There is a BNC connector
to hook directly to my 'scope.

The loads are force-air cooled, and relay switchable for 4,8 and 16 ohms.
When the tester is switched off, the relays drop out, and it defaults back
to 16 ohm load, so you don't accidentally overload the next one on the
bench. I also put in a double bar-graph display, monitoring output waveform
+ / - either side of zero, with a level control. The idea was to be able to
immediately see any lack of symmetry in the output waveform, but I've only
ever had one instance where it did its job. Still, it looks pretty, pumping
away on the front panel, and it soon catches your eye if it stops, and
you've got the squeaker turned down ...

Arfa

N_Cook wrote:
50V , low wattage lamp (or seriesed lower V ones) (assuming normal testing
is 10 to 20W range) to visually show if the volume is set too high, also if
high level high f oscillation on the output; sacrificial, fusewise, if
overdriven.
AC voltmeter , preferably autoranging for possible overload situation, to
measure/long term monitor the RMS power.
High power speaker pot (plus droppers) leading to a low quality ,
sacrificial ( for intitial maybe problematic testing) small speaker, for
basic possible intermittant sound, on/off, indication. Can be switched out
by plugging in a good quality speaker for audio monitoring of quality of
sound issues in otherwise known good amp.
Provision for coupling in a scope for distortion monitoring, when necessary.
Any other add-ons that others know of ?

Mine is made from several lengths of electric fire bar 'tuned' to 8 ohms
each bar. there`s a tap off via a three way speaker selector switch well
resistored down to provide some monitoring using an external speaker. A
couple of capacitors provides DC isolation.

I have one of those Velleman electronic VU meters hooked in which gives
me a rough guide to the input power - the firebars can handle over a
kilowatt, tho they do get pretty hot, the elements glow quite brightly
at those sort of powers.

The front of the case has Speakon,jacks and binding posts.

Originally, I was going to install some kind of cooling fan driven from
DC rectified from the input signal, but never got round to it.

Ron(UK)

"Ron(UK)" wrote in message
news
N_Cook wrote:
50V , low wattage lamp (or seriesed lower V ones) (assuming normal
testing
is 10 to 20W range) to visually show if the volume is set too high, also
if
high level high f oscillation on the output; sacrificial, fusewise, if
overdriven.
AC voltmeter , preferably autoranging for possible overload situation, to
measure/long term monitor the RMS power.
High power speaker pot (plus droppers) leading to a low quality ,
sacrificial ( for intitial maybe problematic testing) small speaker, for
basic possible intermittant sound, on/off, indication. Can be switched
out
by plugging in a good quality speaker for audio monitoring of quality of
sound issues in otherwise known good amp.
Provision for coupling in a scope for distortion monitoring, when
necessary.
Any other add-ons that others know of ?

Mine is made from several lengths of electric fire bar 'tuned' to 8 ohms
each bar. there`s a tap off via a three way speaker selector switch well
resistored down to provide some monitoring using an external speaker. A
couple of capacitors provides DC isolation.

I have one of those Velleman electronic VU meters hooked in which gives me
a rough guide to the input power - the firebars can handle over a
kilowatt, tho they do get pretty hot, the elements glow quite brightly at
those sort of powers.

The front of the case has Speakon,jacks and binding posts.

Originally, I was going to install some kind of cooling fan driven from DC
rectified from the input signal, but never got round to it.

Ron(UK)



You could always buy a cheap fan heater instead, this has a nice 2 or three
speed fan built in. (a tenner from Argos) I tried this but was annoyed
to find that the fan motor was actually 110v, taking its tap from the centre
of the element.


It should be noted though that the element resistance is dependent on its
temperature, so don't bother trying to get any accurate measurements from
this arrangement.


Gareth.

Gareth Magennis wrote:
"Ron(UK)" wrote in message
news
N_Cook wrote:
50V , low wattage lamp (or seriesed lower V ones) (assuming normal
testing
is 10 to 20W range) to visually show if the volume is set too high, also
if
high level high f oscillation on the output; sacrificial, fusewise, if
overdriven.
AC voltmeter , preferably autoranging for possible overload situation, to
measure/long term monitor the RMS power.
High power speaker pot (plus droppers) leading to a low quality ,
sacrificial ( for intitial maybe problematic testing) small speaker, for
basic possible intermittant sound, on/off, indication. Can be switched
out
by plugging in a good quality speaker for audio monitoring of quality of
sound issues in otherwise known good amp.
Provision for coupling in a scope for distortion monitoring, when
necessary.
Any other add-ons that others know of ?
Mine is made from several lengths of electric fire bar 'tuned' to 8 ohms
each bar. there`s a tap off via a three way speaker selector switch well
resistored down to provide some monitoring using an external speaker. A
couple of capacitors provides DC isolation.

I have one of those Velleman electronic VU meters hooked in which gives me
a rough guide to the input power - the firebars can handle over a
kilowatt, tho they do get pretty hot, the elements glow quite brightly at
those sort of powers.

The front of the case has Speakon,jacks and binding posts.

Originally, I was going to install some kind of cooling fan driven from DC
rectified from the input signal, but never got round to it.

Ron(UK)



You could always buy a cheap fan heater instead, this has a nice 2 or three
speed fan built in. (a tenner from Argos) I tried this but was annoyed
to find that the fan motor was actually 110v, taking its tap from the centre
of the element.


It should be noted though that the element resistance is dependent on its
temperature, so don't bother trying to get any accurate measurements from
this arrangement.


True, but most of the time a dummy load is just used for soak testing
at high powers, and remember a real loudspeakers impedance/resistance
also changes appreciably during use.