There's this guy that hangs around recycling in his town and he brings me stuff to fix. A lot of what he brings in is virtually new - it's amazing what people throw away. The other day he brought in what looks like a vintage Ampeg bass speaker cabinet in rough cosmetic shape (name gone), but it has an undamaged 15" speaker installed. It has a 3/4 jack for the input. It has a large square magnet and the numbers on the driver are 5815026 137 544.

My oldest son plays bass in a band but this speaker seems more suited for lower power tube amps. Is this good for a practice amp or better suited for repurposing the cabinet (which is otherwise structurally sound)?

On 03/11/17 06:16, John-Del wrote:
There's this guy that hangs around recycling in his town and he brings me stuff to fix. A lot of what he brings in is virtually new - it's amazing what people throw away. The other day he brought in what looks like a vintage Ampeg bass speaker cabinet in rough cosmetic shape (name gone), but it has an undamaged 15" speaker installed. It has a 3/4 jack for the input. It has a large square magnet and the numbers on the driver are 5815026 137 544.

My oldest son plays bass in a band but this speaker seems more suited for lower power tube amps. Is this good for a practice amp or better suited for repurposing the cabinet (which is otherwise structurally sound)?


Can you post a photo somewhere?

My first bass amp had a 40W valve push-pull output stage,
home-built by an EE friend of my father as a (mono) sound
system sometime in the '50s. It drove a 15" speaker and
a mid-range horn in a beautifully constructed case the
size of a washing machine. The speaker had a powered field
coil!

The whole thing was terribly inefficient by today's standards.
If yours is anything like it I recommend you chuck it and
buy a driver that has modern magnetics.

Also, Phil Allison can probably tell you more about your
Ampeg. His knowledge of such things is legendary.

Clifford Heath.

On Fri, 3 Nov 2017 10:35:35 +1100, Clifford Heath
wrote:


Can you post a photo somewhere?

My first bass amp had a 40W valve push-pull output stage,
home-built by an EE friend of my father as a (mono) sound
system sometime in the '50s. It drove a 15" speaker and
a mid-range horn in a beautifully constructed case the
size of a washing machine. The speaker had a powered field
coil!

The whole thing was terribly inefficient by today's standards.
If yours is anything like it I recommend you chuck it and
buy a driver that has modern magnetics.

Also, Phil Allison can probably tell you more about your
Ampeg. His knowledge of such things is legendary.

Clifford Heath.

Those old powered magnets worked fine, but if the speaker is bad and
needs to be replaced, that magnet usually also served as a choke in the
power supply. This means you cant just eliminate it. You have to either
keep the speaker magnet connected (but not the voice coil), or install a
choke where the speaker coil was connected.

Installing a choke across those two wires is not difficult, but I am not
sure how to determine the choke's size (capacity). Maybe someone else
here will know how to do that. I personally never changed one, but I saw
another guy do it (many years ago), and he explained why. He did not
explain how to get the right size choke though and back then, I did not
bother to ask. I dont know how critical this is..... maybe it's not
critical at all, as long as the choke can handle the voltage and
amperage.

Then again, maybe all those speakers had the same magnet/choke rating.

Any speaker can be reconed too, as long as the frame is not distorted.

On 11/2/2017 7:55 PM, wrote:
Then again, maybe all those speakers had the same
magnet/choke rating.

I guess in your hurry to post, you missed the part
where John said it had a large _magnet_.


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

On 03/11/17 12:00, Foxs Mercantile wrote:
On 11/2/2017 7:55 PM, wrote:
Then again, maybe all those speakers had the same
magnet/choke rating.

I guess in your hurry to post, you missed the part
where John said it had a large _magnet_.

Mine was an electromagnet... which is still a magnet.
But I didn't suggest that his was. Just that magnets
are so much better now, which means efficiency is.

Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Clifford Heath.

Clifford Heath wrote:

---------------------



Can you post a photo somewhere?


Also, Phil Allison can probably tell you more about your
Ampeg. His knowledge of such things is legendary.



** 1960s Ampegs were not sold in Australia, we had a thriving industry in home grown guitar and bass amps back then.

The model in question may well be an Ampeg B15N using a B15NC cabinet fitted with a 15inch Jensen or CTS speaker with square ceramic magnet.

See pics and details he

https://www.talkbass.com/wiki/techni...eaker-cabinet/


..... Phil

On 11/2/2017 8:25 PM, Clifford Heath wrote:
Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.

Several of the vintage radios I have, have electro-
dynamic speakers.


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

Foxs Mercantile wrote:

-------------------------

On 11/2/2017 8:25 PM, Clifford Heath wrote:
Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.


** See link for discussion and details of ED speaker background hum.


https://www.radiomuseum.org/forum/ba...peakers.ht ml


...... Phil

On 03/11/17 13:31, Phil Allison wrote:
Foxs Mercantile wrote:

-------------------------

On 11/2/2017 8:25 PM, Clifford Heath wrote:
Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.


** See link for discussion and details of ED speaker background hum.


https://www.radiomuseum.org/forum/ba...peakers.ht ml

Interesting, thanks Phil. I figured there must be some hum-bucking.

On Friday, November 3, 2017 at 2:48:08 AM UTC-4, Clifford Heath wrote:
On 03/11/17 13:31, Phil Allison wrote:
Foxs Mercantile wrote:

-------------------------

On 11/2/2017 8:25 PM, Clifford Heath wrote:
Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.


so this is interesting and I never thought about it before.

Any ripple in the field winding acts as a MULTIPLICATIVE or MODULATION hum.

What I mean is....consider that there is no audio for a moment applied to moving voice coil. Ripple in the field winding would not then create any audible hum because there is no second field and no force applied. The one field is modulated at 120 Hz but there is no second field from the voice coil. When audio is applied to the voice coil, the modulating field would add AM modulation to the audio.

I imagine it would not sound the same as an ordinary hum.

Anybody actually heard the hum from one of these speakers?


Mark

On Wednesday, 8 November 2017 18:38:56 UTC, wrote:
On Friday, November 3, 2017 at 2:48:08 AM UTC-4, Clifford Heath wrote:
On 03/11/17 13:31, Phil Allison wrote:
Foxs Mercantile wrote:
On 11/2/2017 8:25 PM, Clifford Heath wrote:

Also... as a filter in the power supply? Because yeah,
the one place you really want all that filtered-out
100Hz energy is in your speaker Or perhaps it was
arranged so that enough got through to the amp to
cancel it out? Crazy stuff anyhow.

Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.


so this is interesting and I never thought about it before.

Any ripple in the field winding acts as a MULTIPLICATIVE or MODULATION hum.

What I mean is....consider that there is no audio for a moment applied to moving voice coil. Ripple in the field winding would not then create any audible hum because there is no second field and no force applied. The one field is modulated at 120 Hz but there is no second field from the voice coil. When audio is applied to the voice coil, the modulating field would add AM modulation to the audio.

I imagine it would not sound the same as an ordinary hum.

Anybody actually heard the hum from one of these speakers?


Mark

Yes, and have deliberately produced lf modulation in transistor amps to give them a richer sound. 50/100Hz modulation is largely responsible for the warm sound of old valve radios.


NT

wrote:

-------------------------


Electro-dynamic speakers had the filed coil which
doubled as the power supply filter choke.
Alon with the voice coil, there was a hum-bucking coil
that canceled the residual hum from the field winding.


so this is interesting and I never thought about it before.

Any ripple in the field winding acts as a MULTIPLICATIVE or MODULATION hum.

What I mean is....consider that there is no audio for a moment applied to moving voice coil. Ripple in the field winding would not then create any audible hum because there is no second field and no force applied. The one field is modulated at 120 Hz but there is no second field from the voice coil. When audio is applied to the voice coil, the modulating field would add AM modulation to the audio.

I imagine it would not sound the same as an ordinary hum.

Anybody actually heard the hum from one of these speakers?


** There is background hum caused by injection of field coil ripple current INTO the voice coil of the same speaker. If the VC were left unconnected, there is no circuit and so no hum.

When the VC is connected to the OP tranny, hum is audible from this source PLUS
residual from the ripple on the supply rail that is not rejected by a single ended tube stage.

Modulation of the audio because of varying filed strength in the magnetic gap is small, since the iron parts are pushed well into saturation.


..... Phil

** There is background hum caused by injection of field coil ripple current INTO the voice coil of the same speaker. If the VC were left unconnected, there is no circuit and so no hum.


good point, thanks



When the VC is connected to the OP tranny, hum is audible from this source PLUS
residual from the ripple on the supply rail that is not rejected by a single ended tube stage.

Modulation of the audio because of varying filed strength in the magnetic gap is small, since the iron parts are pushed well into saturation.


.... Phil

ok, thank you

m