16 ohm amp --> 4 ohm speaker block (ex speakers)

[N Cook]

Could a Crate BV120H valve amp really blow 4x 12 inch 16 ohm speaker box ?
Amp as received was set for 16 ohm output, I measured the speaker box
impedance at 13 ohm, or so, before connecting up just to be sure.
Very feeble and distorted sound. No signs of the reported burning smell,
output matching transformer primaries at about 50 ohm seemed ok and
secondaries not open circuit in the amp so turned to the speakers. The amp
o/p switch setting was set for 4 ohms instead of 16 ohms but as I measured
16 ohms I assumed a switch problem.
Taking apart 2 pairs of paralleled 16 ohm speakers so settable as series
pair of 8 ohm for 16, or 4 paralleled for 4 ohm.
3 of these speakers are open circuit leaving one giving the 16 ohm reading ,
and the fourth one driving from another source is distorting.
Can a valve amp really progressively burn out, in turn, 16 ohm speakers ?
Driving just one initially, I could understand, like the final remnant one
here.

 

[N Cook]

replace

The amp
o/p switch setting was set for 4 ohms instead of 16 ohms but as I measured
16 ohms I assumed a switch problem.

with

The switch setting on the speaker box was set for 4 ohms instead of 16 ohms
but as I measured16 (13) ohms I assumed a switch problem.

 

[Stephen Cowell]

Could a Crate BV120H valve amp really blow 4x 12 inch 16 ohm speaker box ?
Amp as received was set for 16 ohm output, I measured the speaker box
impedance at 13 ohm, or so, before connecting up just to be sure.
Very feeble and distorted sound. No signs of the reported burning smell,
output matching transformer primaries at about 50 ohm seemed ok and
secondaries not open circuit in the amp so turned to the speakers. The amp
o/p switch setting was set for 4 ohms instead of 16 ohms but as I measured
16 ohms I assumed a switch problem.

It sounds like the speakers were blown before this exercise
started... what you did (with no loud noise) should not have
blown any speakers... *maybe* the amp could suffer, but
not the speakers.
__
Steve
..

 

[N Cook]

It sounds like the speakers were blown before this exercise
started... what you did (with no loud noise) should not have
blown any speakers... *maybe* the amp could suffer, but
not the speakers.
__
Steve
.

Reasonably easy to cleanly remove one of the cones.
If a next time, to cleanly remove the dust skirt I will make a small hole
and pull with a sickle probe to cleanly remove that section.
No sign of burning on the voice coil so I could count the number of turns in
both layers if I was to rewind another. But the cardboard core that this
coil was on has broken up completely . Not knowing how to do precision
origami , looks like the end of that one.

If there is power for power no audio difference between a 16 and 4 ohm
speaker, is there an advantage to protecting amps or speakers to opt for 2
pairs of parallel 16 ohm for 4 ohms overall or 2 seriesed 4 ohms in parallel
with same for 4 ohms. For 16 ohm setting for the last one of 4 4 ohm in
series then if 1 goes o/c then that would protect the others

 

[Ron(UK)]

Reasonably easy to cleanly remove one of the cones.
If a next time, to cleanly remove the dust skirt I will make a small hole
and pull with a sickle probe to cleanly remove that section.
No sign of burning on the voice coil so I could count the number of turns in
both layers if I was to rewind another. But the cardboard core that this
coil was on has broken up completely . Not knowing how to do precision
origami , looks like the end of that one.

If the voice coil former was destroyed, that would indicate that the
speaker had been vastly overloaded for a fair period of time. voice
coils dont usually go o/c without showing signs of either burning or
rubbing, tho they do sometimes go o/c in the short length between the
coil and the pigtails.
Did you check the continuity of the pigtails from the tags to the cone?,
they can sometimes look ok but be o/c. It`s often fairly easy to slice
out the dust dome with a razor blade, and solder new braids to the v/c -
there are usually solder blobs under some black paint like substance -
then glue the original dome back in.

I doubt that the original speakers are worth reconing, but, Wembley
Loudspeakers will sell you voice coils, cones etc., if you know what you
want, and ask them nicely.

Ron(UK)

 

[RonSonic]

Reasonably easy to cleanly remove one of the cones.
If a next time, to cleanly remove the dust skirt I will make a small hole
and pull with a sickle probe to cleanly remove that section.
No sign of burning on the voice coil so I could count the number of turns in
both layers if I was to rewind another. But the cardboard core that this
coil was on has broken up completely . Not knowing how to do precision
origami , looks like the end of that one.

Voice coils, cones and spiders are all replacement parts. Just that I don't know
who to get them from in your neighborhood.

I don't think it is so much an issue of the amp damaging the speakers as in your
original question, but of speakers simply failing as they will. There are a lot
of very cheap speakers out there now. Tube amps don't fail by generating a DC
offset on the output like solid state stuff will.

If there is power for power no audio difference between a 16 and 4 ohm
speaker, is there an advantage to protecting amps or speakers to opt for 2
pairs of parallel 16 ohm for 4 ohms overall or 2 seriesed 4 ohms in parallel
with same for 4 ohms. For 16 ohm setting for the last one of 4 4 ohm in
series then if 1 goes o/c then that would protect the others

There are some tonal differences in how the speakers are connected. I'll suggest
that your series arrangement is a poor choice - true if one speaker goes open it
protects the others - however tube amps really, really dislike throwing signal
at an open load. Often the unterminated output transformer will do a flyback
phenomenon that puts several thousand volts across the primary and arcing tubes,
sockets or the tranny.

I'd stick with series-parallel as traditional for a 4x12, just do it with better
drivers or a higher quality recone on those.

Ron

 

[Jim]

Could a Crate BV120H valve amp really blow 4x 12 inch 16 ohm speaker box ?

Yes, if speakers can't handle 30W.

Amp as received was set for 16 ohm output, I measured the speaker box
impedance at 13 ohm,

You mean you measured DCR, DC resistance. 13 is typical for 16 ohm
speakers.

or so, before connecting up just to be sure.

Very feeble and distorted sound. No signs of the reported burning smell,
output matching transformer primaries at about 50 ohm seemed ok and
secondaries not open circuit in the amp so turned to the speakers. The amp
o/p switch setting was set for 4 ohms instead of 16 ohms but as I measured
16 ohms I assumed a switch problem.

You can get flyback voltages sufficient to punch through windings in the
OPT, or sufficient to arc tube sockets. If it was good before the
mistake, and bad after, the answer is obvious.

Taking apart 2 pairs of paralleled 16 ohm speakers so settable as series
pair of 8 ohm for 16, or 4 paralleled for 4 ohm.
3 of these speakers are open circuit leaving one giving the 16 ohm reading ,
and the fourth one driving from another source is distorting.

Wait a minute. Conventionally wired 16 ohm cab with 16 ohms speakers
will have NO SOUND if three speakers are blown.

 

[N Cook]

?

Yes, if speakers can't handle 30W.



You mean you measured DCR, DC resistance. 13 is typical for 16 ohm
speakers.

or so, before connecting up just to be sure.

You can get flyback voltages sufficient to punch through windings in the
OPT, or sufficient to arc tube sockets. If it was good before the
mistake, and bad after, the answer is obvious.



Wait a minute. Conventionally wired 16 ohm cab with 16 ohms speakers
will have NO SOUND if three speakers are blown.

it would progressively have failed from collective 4 ohm to 5.3 to 8 to the
current overdriven and useless single 16 ohm one

 

[Ron(UK)]

it would progressively have failed from collective 4 ohm to 5.3 to 8 to the
current overdriven and useless single 16 ohm one

Are you saying that the four speakers were all wired in parallel, to
give 4 ohms? That`s unusual for a 4x12 guitar cab. they would usually
be in series/parallel, giving 16 ohms, and allowing two cabinets to be
used with the amp. In which case, if any one speaker went o/c, its
'series twin' would stop receiving power but the other pair would still
work - until they were overloaded and blew.

Ron(UK)

 

[N Cook]

Are you saying that the four speakers were all wired in parallel, to
give 4 ohms? That`s unusual for a 4x12 guitar cab. they would usually
be in series/parallel, giving 16 ohms, and allowing two cabinets to be
used with the amp. In which case, if any one speaker went o/c, its
'series twin' would stop receiving power but the other pair would still
work - until they were overloaded and blew.

Ron(UK)

Crate BV412R, Blue Voodoo
2 separate permanently wired paralleled pairs of 16 ohms so 9 ohms each
section.
Switched so they are in series to give 8 + 8 = 16
or paralleled to give 8//8 = 4 , ie all 4 in paralle

 

[Xtrchessreal]

Crate BV412R, Blue Voodoo
2 separate permanently wired paralleled pairs of 16 ohms so 9 ohms each
section.
Switched so they are in series to give 8 + 8 = 16
or paralleled to give 8//8 = 4 , ie all 4 in paralle

I want to jump in here and ask another related question.

It sounds like there are at least two ways to wire a 16 Ohm 4x12 cab.
One way explained above where two pairs are 16//16 and then those are
series 8+8. Another way would be series two pairs 16+16 and then
32//32 to give 16.

Reading the discussion above it sounds like if the cab was wired like
the latter above a pair of the speakers in the cab blowing would have
meant the amp seeing 32 Ohms and the rest would not have happened.
Saving half of the speakers and the amp.

Is this correct?

 

[N Cook]

I want to jump in here and ask another related question.

It sounds like there are at least two ways to wire a 16 Ohm 4x12 cab.
One way explained above where two pairs are 16//16 and then those are
series 8+8. Another way would be series two pairs 16+16 and then
32//32 to give 16.

Reading the discussion above it sounds like if the cab was wired like
the latter above a pair of the speakers in the cab blowing would have
meant the amp seeing 32 Ohms and the rest would not have happened.
Saving half of the speakers and the amp.

Is this correct?

But how to wire 4x 16 ohmers for overal 4 ohm and best amp protection and/or
speaker preservation ? It is the 4 ohm setting that is likely to lead to
troubles in incompetent hands or even maybe persons deliberately getting
more welly