Here is something that has puzzled me.

Battery-powered TRFs typically have connections for an external high-impedance speaker. Most of these sets (seems like virtually all manufacturers) label the two speaker connections as: + and -. Why? What difference does in make?

Speakers of the same vintage usually do not have polarity markings, so the radio's connections wouldn't be possible to follow anyway.

I understand the necessity for stereo speaker pairs to be matched, polarity-wise. But this was long before stereo.

Hi Doug

On some of these old high impedance speakers polarity matters. There is DC going through the speaker as well as the AC signal. DC can pull the cone or diaphram so far as to make contact. It has to float for loudest and least distorted sound.

Best to use a choke from output tube to B+. Then cap couple plate to the speaker. This way no DC goes through your speaker.

Norm

:Here is something that has puzzled me.
:
:Battery-powered TRFs typically have connections for an external high-impedance speaker. Most of these sets (seems like virtually all manufacturers) label the two speaker connections as: + and -. Why? What difference does in make?
:
:Speakers of the same vintage usually do not have polarity markings, so the radio's connections wouldn't be possible to follow anyway.
:
:I understand the necessity for stereo speaker pairs to be matched, polarity-wise. But this was long before stereo.
:

Doug:

This is interesting. Can you give me an example of a TRF with speaker polarity markings? I would like to look at the schematic.

Gary

:Here is something that has puzzled me.
:
:Battery-powered TRFs typically have connections for an external high-impedance speaker. Most of these sets (seems like virtually all manufacturers) label the two speaker connections as: + and -. Why? What difference does in make?
:
:Speakers of the same vintage usually do not have polarity markings, so the radio's connections wouldn't be possible to follow anyway.
:
:I understand the necessity for stereo speaker pairs to be matched, polarity-wise. But this was long before stereo.
:

Doug:

This is interesting. Can you give me an example of a TRF with speaker polarity markings? I would like to look at the schematic.

Gary

:Here is something that has puzzled me.
:
:Battery-powered TRFs typically have connections for an external high-impedance speaker. Most of these sets (seems like virtually all manufacturers) label the two speaker connections as: + and -. Why? What difference does in make?
:
:Speakers of the same vintage usually do not have polarity markings, so the radio's connections wouldn't be possible to follow anyway.
:
:I understand the necessity for stereo speaker pairs to be matched, polarity-wise. But this was long before stereo.
:

Gary, take a look, for example, at the schematic for a Stewart-Warner Model 300, c. 1925:
http://www.nostalgiaair.org/PagesByModel/794/M0029794.pdf

This is pretty much a garden-variety TRF - with five '01A triode tubes and three tuning dials. The speaker terminals are marked positive and negative (on both the set itself and on the schematic).

Norm's explanation makes sense to me. However, none of my high-impedance speakers seem to have polarity markings.

:
:Doug:
:
:This is interesting. Can you give me an example of a TRF with speaker polarity markings? I would like to look at the schematic.
:
:Gary
:
::Here is something that has puzzled me.
::
::Battery-powered TRFs typically have connections for an external high-impedance speaker. Most of these sets (seems like virtually all manufacturers) label the two speaker connections as: + and -. Why? What difference does in make?
::
::Speakers of the same vintage usually do not have polarity markings, so the radio's connections wouldn't be possible to follow anyway.
::
::I understand the necessity for stereo speaker pairs to be matched, polarity-wise. But this was long before stereo.
::

If I remember correctly it has to due with the phasing of the speakers. Not stereo but consider two speakers hooked up in parallel and an AC signal passing through the voice coils of both would would be in phase, e.g. they go positive and negative at the same time.The magnetic field of each speaker let's assume are north pole to the front and south pole to the back. Now depending on how the AC enters the voice coil the speakers will either be pulled back or pushed forward by the magnetic field. When DC is applied to a coil (voice coil in this instance) depending on how it is wound, one end will be north and one end will be south. Again, if memory serves me correctly there was a "Faradays left hand rule" which basically stated that if you place your left hand around the coil with your fingers going with the windings your thumb points to north pole of magnet. Now at any instant AC is DC (flowing in one direction and thus voice coil will have a north pole and a south pole and be repelled or attracted to the speakers magnetic field (which does not change). So now if the AC enters the voice coil from a different end of the winding on the two speakers,one speaker cone will be repelled and one speaker cone will be attracted by the magnet. What happens then is that you produce the same tone but the air movement producing the tone is traveling in a diffewrent direction from each speaker. I have "tin" ears (crazy for an ex-Navy sonarmenn) and can't tell the differance but someone with a good ear for music would. The phasing of the speakers has to do more with the mechanical aspects (movement of air)of the speaker as opposed to electrical. I hope I described this clearly, if not I'll try to clarify. PL

Hi Doug

The flexible wire used on old speakers sometimes has one lead striped. This was to indicate polarity. I had a few speakers lock up when connected in reverse. One was a cone type from around 1928 by Columbia.

Norm

:Gary, take a look, for example, at the schematic for a Stewart-Warner Model 300, c. 1925:
: http://www.nostalgiaair.org/PagesByModel/794/M0029794.pdf
:
:This is pretty much a garden-variety TRF - with five '01A triode tubes and three tuning dials. The speaker terminals are marked positive and negative (on both the set itself and on the schematic).
:
:Norm's explanation makes sense to me. However, none of my high-impedance speakers seem to have polarity markings.
:
:
:
::
::Doug:
::
::This is interesting. Can you give me an example of a TRF with speaker polarity markings? I would like to look at the schematic.
::
::Gary
::
:::Here is something that has puzzled me.
:::
:::Battery-powered TRFs typically have connections for an external high-impedance speaker. Most of these sets (seems like virtually all manufacturers) label the two speaker connections as: + and -. Why? What difference does in make?
:::
:::Speakers of the same vintage usually do not have polarity markings, so the radio's connections wouldn't be possible to follow anyway.
:::
:::I understand the necessity for stereo speaker pairs to be matched, polarity-wise. But this was long before stereo.
:::