Hi,

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo has
a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

However, I'm trying to work out the best way to stick a removeable
attenuator between the amp and the speaker, and I have a plan of just
putting another switching 1/4" jack in the speaker cable between the
amp output and the speaker. I could take the feed to the attenuator
from the extension cab socket and then feed it back to the speaker via
the new jack, but I'm a bit concerned that when the attenuator is not
connected (and therefore when I'm gigging with it), the signal will now
be going through two 'empty' 1/4" jacks instead of just the one - and
that may increase the chances of failure at a gig - especially if 1/4"
jacks aren't really designed to handle 15 watts of amp output.

What do you think ?

Cheers,

Kev.

wrote:
Hi,

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo has
a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

However, I'm trying to work out the best way to stick a removeable
attenuator between the amp and the speaker, and I have a plan of just
putting another switching 1/4" jack in the speaker cable between the
amp output and the speaker. I could take the feed to the attenuator
from the extension cab socket and then feed it back to the speaker via
the new jack, but I'm a bit concerned that when the attenuator is not
connected (and therefore when I'm gigging with it), the signal will now
be going through two 'empty' 1/4" jacks instead of just the one - and
that may increase the chances of failure at a gig - especially if 1/4"
jacks aren't really designed to handle 15 watts of amp output.

Since most amp manufacturers routinely use 1/4" jacks
for amps up to 100 watts I think we'd all know by now if
there were any serious issues with doing so.
Several 1/4" jacks in series ought to easily handle 15 watts.

rd

RD Jones wrote:
wrote:

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo has
a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

However, I'm trying to work out the best way to stick a removeable
attenuator between the amp and the speaker, and I have a plan of just
putting another switching 1/4" jack in the speaker cable between the
amp output and the speaker. I could take the feed to the attenuator
from the extension cab socket and then feed it back to the speaker via
the new jack, but I'm a bit concerned that when the attenuator is not
connected (and therefore when I'm gigging with it), the signal will now
be going through two 'empty' 1/4" jacks instead of just the one - and
that may increase the chances of failure at a gig - especially if 1/4"
jacks aren't really designed to handle 15 watts of amp output.

Since most amp manufacturers routinely use 1/4" jacks
for amps up to 100 watts I think we'd all know by now if
there were any serious issues with doing so.

The main issue is that the hot pin (i.e. the tip) is unprotected and can
give a shock if the amp is powerful enough. 15 watts, no real problem.
But 1000 watts? That's almost 90 volts assuming an 8 ohm load. Not
recommended.

Another problem is that it can short to ground, and most amps don't like
operating into a zero ohm load. Some hate it so much they commit
suicide if you try to make them do it.



//Walt

wrote:

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo has
a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

I dunno. With 15 watts, it's not going to get hot, but it will still be
unreliable when the connectors get old. Do you care about that?

However, I'm trying to work out the best way to stick a removeable
attenuator between the amp and the speaker, and I have a plan of just
putting another switching 1/4" jack in the speaker cable between the
amp output and the speaker. I could take the feed to the attenuator
from the extension cab socket and then feed it back to the speaker via
the new jack, but I'm a bit concerned that when the attenuator is not
connected (and therefore when I'm gigging with it), the signal will now
be going through two 'empty' 1/4" jacks instead of just the one - and
that may increase the chances of failure at a gig - especially if 1/4"
jacks aren't really designed to handle 15 watts of amp output.

15 watts is nothing.. I see guys running hundreds of watts through 1/4"
jacks. Which is a bad idea if you ask me, but people do it.

If I were you, I'd use Speakons. They are designed for the job, more
reliable for the application, and lock in place. The disadvantages are
that they don't make switching ones, and they can be difficult to find at
four in the morning when you have to improvise something.

What do you think ?

I think you can do better than 1/4" but you can do worse too.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

wrote:

Hi,

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ?

Bewa

If anyone trips on the cable and pulls the plug out, the amp will be
left without a load. This doesn't matter to a transistor amp, but a
valve amplifier with an unloaded output transformer will develop very
high internal voltages. These can flash-over inside the valves, arc
across the valve bases or burn through the insulation inside the output
transformer.

Some valve amplifiers used to arrange a loading resistor which was
switched across the transformer secondary when the jack plug was removed
from the amp, but that doesn't protect it if the plug comes out at the
speaker end.

I would be inclined to use some sort of captive connector and
permanently wire a resistor (68 ohms 2 watts) across the back of the
speaker terminals inside the amplifier. The loss of a couple of watts
is trivial compared with the cost of repair if anything goes badly
wrong.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Walt wrote:

Another problem is that it can short to ground

As it's a valve (US:tube) amplifier in this case, that won't be a problem.

--
Anahata
-+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo has
a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

Never mind the type of plug, it is important that tube amps are connected to
the proper impedence to avoid damage to expensive components (the tubes and
output transformer). Attenuating a tube amp's output is generally a bad
idea, and trying to get more "tube sound" from a modern tube amp by driving
it hard isn't especially effective.

Frankly with the effectiveness of tube modeling devices these days, there's
scant reason to use tube amps anymore unless you go vintage.

wrote:
Hi,

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo
has a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

A 1/4 jack will short-circuit the output of a tube and of any power just as
well as it will a solid state one.

So no problem to use one if you ensure good insulation of centre pin, and
that it is solidly inserted and remains that way while amp switched on.

As for your atten idea, that's a whole story in itself.

geoff

Zigakly wrote:

Never mind the type of plug, it is important that tube amps are connected to
the proper impedence to avoid damage to expensive components (the tubes and
output transformer). Attenuating a tube amp's output is generally a bad
idea, and trying to get more "tube sound" from a modern tube amp by driving
it hard isn't especially effective.

Why? The whole point of using a proper attenuator is that the amp DOES see
the correct impedance.

Now, admittedly you don't get the speaker break-up at high levels that you
do running the amp full out, and that misses a whole lot of the tone, but
that's just a sonic issue, not a question of doing damage.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

they don't REALLY commit suicide, what actually happens is that you let the
smoke out of the resistors, capacitors and power transistors... ) kk


--
=Kevin Kienlein - Entertainer/Inspirational Speaker
=Vernon, BC, Canada
=See my NEW WEBSITE http://www.kevinkienlein.com
=Never give in, NEVER, NEVER, NEVER!
=Life is the Gig, THIS AIN'T NO REHEARSAL!
=Age 45/Tricuspid, Atresia, Atrial & Vent, Septal Defects.
=My Congenital Heart Defects

"Walt" wrote in message
...
RD Jones wrote:
wrote:

I know that using 1/4" jacks for speakers is generally frowned upon,
but - is it ok for using with a 15 watt valve amp ? My Laney combo has
a built-in switched 1/4" jack for an extension speaker cabinet -
cutting out the internal speaker when used, so Laney obviously think
it'll do.

However, I'm trying to work out the best way to stick a removeable
attenuator between the amp and the speaker, and I have a plan of just
putting another switching 1/4" jack in the speaker cable between the
amp output and the speaker. I could take the feed to the attenuator
from the extension cab socket and then feed it back to the speaker via
the new jack, but I'm a bit concerned that when the attenuator is not
connected (and therefore when I'm gigging with it), the signal will now
be going through two 'empty' 1/4" jacks instead of just the one - and
that may increase the chances of failure at a gig - especially if 1/4"
jacks aren't really designed to handle 15 watts of amp output.

Since most amp manufacturers routinely use 1/4" jacks
for amps up to 100 watts I think we'd all know by now if
there were any serious issues with doing so.

The main issue is that the hot pin (i.e. the tip) is unprotected and can
give a shock if the amp is powerful enough. 15 watts, no real problem.
But 1000 watts? That's almost 90 volts assuming an 8 ohm load. Not
recommended.

Another problem is that it can short to ground, and most amps don't like
operating into a zero ohm load. Some hate it so much they commit suicide
if you try to make them do it.



//Walt

Attenuating a tube amp's output is generally a bad
idea, and trying to get more "tube sound" from a modern tube amp by
driving
it hard isn't especially effective.

Why? The whole point of using a proper attenuator is that the amp DOES
see
the correct impedance.

If you're implying that modern tube amps are paired with speakers of the
wrong impedance, that's news to me. However, the OP is definitely not
trying to compensate for any such issue.

Now, admittedly you don't get the speaker break-up at high levels that you
do running the amp full out, and that misses a whole lot of the tone, but
that's just a sonic issue, not a question of doing damage.

We're talking about a small Laney combo here, not a vintage plexi stack.
There is no significant tone to be expropriated, only damage in the trying.

On Fri, 19 May 2006 22:39:27 +0100, lid
(Adrian Tuddenham) wrote:

If anyone trips on the cable and pulls the plug out, the amp will be
left without a load. This doesn't matter to a transistor amp, but a
valve amplifier with an unloaded output transformer will develop very
high internal voltages. These can flash-over inside the valves, arc
across the valve bases or burn through the insulation inside the output
transformer.

I used valve amps back when they were all there was. I'm sure
speaker cables (on 1/4" jacks) got pulled out sometimes. I can't
remember an amp ever blowing up though. Just how worried SHOULD we
be?

"Laurence Payne" lpayne1NOSPAM@dslDOTpipexDOTcom wrote in message
...
On Fri, 19 May 2006 22:39:27 +0100, lid
(Adrian Tuddenham) wrote:

If anyone trips on the cable and pulls the plug out, the amp will be
left without a load. This doesn't matter to a transistor amp, but a
valve amplifier with an unloaded output transformer will develop very
high internal voltages. These can flash-over inside the valves, arc
across the valve bases or burn through the insulation inside the output
transformer.

I used valve amps back when they were all there was. I'm sure
speaker cables (on 1/4" jacks) got pulled out sometimes. I can't
remember an amp ever blowing up though. Just how worried SHOULD we
be?

Most amps have some sort of feedback circuit around the output stages, and
that should keep problems like this under control. If you're using an amp
with absolutely no feedback loop, then worry. (A few single-ended guitar
amps ran open-loop. But they were inevitably combo amps, so the odds of
having the speaker cable pull out were pretty slim.) Otherwise relax.

Peace,
Paul

Paul Stamler wrote:

"Laurence Payne" lpayne1NOSPAM@dslDOTpipexDOTcom wrote in message
...
On Fri, 19 May 2006 22:39:27 +0100, lid
(Adrian Tuddenham) wrote:

If anyone trips on the cable and pulls the plug out, the amp will be
left without a load. This doesn't matter to a transistor amp, but a
valve amplifier with an unloaded output transformer will develop very
high internal voltages. These can flash-over inside the valves, arc
across the valve bases or burn through the insulation inside the output
transformer.

I used valve amps back when they were all there was. I'm sure
speaker cables (on 1/4" jacks) got pulled out sometimes. I can't
remember an amp ever blowing up though. Just how worried SHOULD we
be?

Most amps have some sort of feedback circuit around the output stages, and
that should keep problems like this under control. If you're using an amp
with absolutely no feedback loop, then worry. (A few single-ended guitar
amps ran open-loop. But they were inevitably combo amps, so the odds of
having the speaker cable pull out were pretty slim.) Otherwise relax.

The chance of a flashover is greatly increased if you are running the
amp up to distortion levels, where the feedback is hardly in control and
there is a lot of energy stored in the output transformer at each
half-cycle. It is even possible that the feedback on an unloaded
amplifier is no longer stable.

It seemed to me that the O/P might want use the amplifier flat-out for
the distortion effect it would produce. Guitar amplifiers have less
feedback than Hi-Fi amplifiers so as to run into distortion more
gradually.

Flashover is a real possibility, I have known it happen on several
occasions and have seen the aftermath on units brought in for repair:
shorted turns in output transformers and carbonised tracks burned across
valvholders. Remember, it is not unusual to have 700v between anodes on
a relatively small output stage which is working as intended - when it
is unloaded, this can easily rise to several kilovolts.


I still use a valve amplifier occasionally for 100v line P.A. work - I
designed it to cope with all kinds of load mismatching and there is a
permanent loading resistor wired across the output - but I still
wouldn't knowingly leave it running off-load for any length of time.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

On Sat, 20 May 2006 19:54:01 +0100, Laurence Payne
lpayne1NOSPAM@dslDOTpipexDOTcom wrote:

I used valve amps back when they were all there was. I'm sure
speaker cables (on 1/4" jacks) got pulled out sometimes. I can't
remember an amp ever blowing up though. Just how worried SHOULD we
be?

The nature of the problem is flashover from too high an
instantaneous voltage. I've also never seen it, but can
imagine it being a problem if the amplifier oscillates
or is otherwise overdriven without damping. An ordinary
Zobel network across the output should be sufficient.

IOW, there's nothing magic about being unloaded, but
the amplifier can generate big voltages with big dI/dt's.
Easy enough to scotch.

All good fortune,

Chris Hornbeck

Zigakly wrote:
Attenuating a tube amp's output is generally a bad
idea, and trying to get more "tube sound" from a modern tube amp by
driving
it hard isn't especially effective.

Why? The whole point of using a proper attenuator is that the amp DOES
see
the correct impedance.

If you're implying that modern tube amps are paired with speakers of the
wrong impedance, that's news to me. However, the OP is definitely not
trying to compensate for any such issue.

No. An attenuator is an L-pad. You have an 8-ohm source coming out of
the amp. That goes into an attenuator. The input impedance and the
output impedance of the attenuator are both 8 ohms. It goes to a speaker
that is an 8-ohm load.

The whole point of the attenuator is that it's NOT just a series resistor,
and it presents the proper load to the amplifier.

Now, admittedly you don't get the speaker break-up at high levels that you
do running the amp full out, and that misses a whole lot of the tone, but
that's just a sonic issue, not a question of doing damage.

We're talking about a small Laney combo here, not a vintage plexi stack.
There is no significant tone to be expropriated, only damage in the trying.

Hey, there's even interesting tone due to cone breakup in a Pignose.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Chris Hornbeck wrote:
On Sat, 20 May 2006 19:54:01 +0100, Laurence Payne
lpayne1NOSPAM@dslDOTpipexDOTcom wrote:

I used valve amps back when they were all there was. I'm sure
speaker cables (on 1/4" jacks) got pulled out sometimes. I can't
remember an amp ever blowing up though. Just how worried SHOULD we
be?

The nature of the problem is flashover from too high an
instantaneous voltage. I've also never seen it, but can
imagine it being a problem if the amplifier oscillates
or is otherwise overdriven without damping. An ordinary
Zobel network across the output should be sufficient.

The thing is, back when valve amps were all that there was, if you
blew out a pair of 6550s, it was just a trip to the corner drugstore
to pick up a couple. At worst you'd have to go to the local TV repair
shop.

These days, it's a bit more difficult, and a whole lot more expensive,
so things that once were considered perfectly reasonable aren't any longer.

Back in the sixties, the response to cathode stripping problems was just
to preventatively replace tubes. These days people look at you like an
alien if you suggest that.

IOW, there's nothing magic about being unloaded, but
the amplifier can generate big voltages with big dI/dt's.
Easy enough to scotch.

Right, and if the transformer rings badly when it's unloaded, the
possibility of damage is worse because you can generate pretty high
peak voltages.

Not to mention the absolute embarassment on stage. "Sorry, man, I tripped
over the cable and it came out." With a speakon it won't come out. Then
again, you might knock the whole stack down instead.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:


No. An attenuator is an L-pad. You have an 8-ohm source coming out of
the amp. That goes into an attenuator. The input impedance and the
output impedance of the attenuator are both 8 ohms. It goes to a speaker
that is an 8-ohm load.

If it presents an 8 ohm impedance in both directions, it would have to
be 'pi' network (at the very least). A simple 'L' wouldn't do that.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Adrian Tuddenham wrote:
Scott Dorsey wrote:

No. An attenuator is an L-pad. You have an 8-ohm source coming out of
the amp. That goes into an attenuator. The input impedance and the
output impedance of the attenuator are both 8 ohms. It goes to a speaker
that is an 8-ohm load.

If it presents an 8 ohm impedance in both directions, it would have to
be 'pi' network (at the very least). A simple 'L' wouldn't do that.

Actually most are L-pads, so the speaker sees a lower than usual impedance.
I'd be curious if going to a T-pad instead would change the sound in any
audible way. The low end might be affected by the source Z.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

(Scott Dorsey) wrote in
:

Adrian Tuddenham wrote:
Scott Dorsey wrote:

No. An attenuator is an L-pad. You have an 8-ohm source
coming out of the amp. That goes into an attenuator. The
input impedance and the output impedance of the attenuator
are both 8 ohms. It goes to a speaker that is an 8-ohm
load.

If it presents an 8 ohm impedance in both directions, it would
have to be 'pi' network (at the very least). A simple 'L'
wouldn't do that.

Actually most are L-pads, so the speaker sees a lower than
usual impedance. I'd be curious if going to a T-pad instead
would change the sound in any audible way. The low end might
be affected by the source Z. --scott

Usually, the output of an amplifier is also much less that the
rated impedance (damping factor). For tube amps, the output of
the attenuator is about the same. For solid-state amps, the
damping factor is worsened by the attenuator.

Going to a T-pad would be much bad.

--
Bob Quintal

PA is y I've altered my email address.