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Hi Everyone.
Does anyone know what the actual differences are between the Jensen V20 used in the earlier Leslies and the Jensen V21 used in most Leslies from the 1950's up to the 1970's?
I have read that the V20 produces a brighter treble response than the V21.
One factor that definitely contributes to the mellower sound of the V21 is the little cork plug and the little cotton ball underneath the cork plug which are located on the middle hole on top of the cone shaped black bakelite phase plug on the V21.
The Jensen V21 was also used in the Jensen RP201 mid-range horn which was used together with the Jensen P15LL bass speaker in the 1950's era Jensen "build it yourself" hi-fi speaker systems.
The black bakelite phase plug of the V21 used in the RP201 midrange horn does not have the cork plug or the little cotton ball.
The fact that the V21 phase plug was manufactured with the hole in the middle top of the phase plug suggests the possibility that the cork plug and the little cotton ball beneath the cork plug were only added specifically for the V21's sold to Leslie, either by the Jensen employees or by the Leslie employees in order to mellow down the treble response and therefore reduce the key click sound.
Last month out of curiosity I removed the cork plug and the little cotton ball from the phase plug of the V21 in my Leslie.
Overall the V21 still sounds like a V21 but with a brighter high treble response which is most noticeable in the high treble distortion harmonics when using the overdrive unit.
I can restore the stock mellower V21 tonality by plugging up the middle hole on the phase plug with a blob of Blu-Tak.
I also have an Eden/Hammond Suzuki 100 watt Ferro Fluid driver, and the conical shaped white plastic phase plug of the Ferro Fluid driver appears to be based on the design of the V21 phase plug shape including the middle hole on the top of the cone shaped phase plug.
I plugged up this middle hole by inserting a blob of Blu-Tac in the hole, and this resulted in a noticeable difference in the tonality of the Ferro Fluid driver by mellowing down the treble response and therefore reducing the bright harsh edginess of the sound.
Whilst the Ferro Fluid driver with the plugged up phase plug middle hole still sounds different from the V21, it does sound mellower and less harsh so therefore I do recommend this very simple modification for those who have Ferro Fluid drivers in their Leslies and they do not like the harsh edgy sound.
The attached photos here below show the Jensen V21 with the stock cork plug in the phase plug middle hole, and then with the cork plug removed exposing the little cotton ball normally hidden underneath the cork plug.
There is also a photo of a Jensen V21 in the Jensen RP201 midrange horn and there is no cork plug in the phase plug middle hole.
There is also a photo of the Ferro Fluid driver with the stock phase plug middle hole visible, and then with the middle hole plugged up with Blu-Tak in order to mellow down the treble response.
All the best.
Kon.
Does anyone know what the actual differences are between the Jensen V20 used in the earlier Leslies and the Jensen V21 used in most Leslies from the 1950's up to the 1970's?
I have read that the V20 produces a brighter treble response than the V21.
One factor that definitely contributes to the mellower sound of the V21 is the little cork plug and the little cotton ball underneath the cork plug which are located on the middle hole on top of the cone shaped black bakelite phase plug on the V21.
The Jensen V21 was also used in the Jensen RP201 mid-range horn which was used together with the Jensen P15LL bass speaker in the 1950's era Jensen "build it yourself" hi-fi speaker systems.
The black bakelite phase plug of the V21 used in the RP201 midrange horn does not have the cork plug or the little cotton ball.
The fact that the V21 phase plug was manufactured with the hole in the middle top of the phase plug suggests the possibility that the cork plug and the little cotton ball beneath the cork plug were only added specifically for the V21's sold to Leslie, either by the Jensen employees or by the Leslie employees in order to mellow down the treble response and therefore reduce the key click sound.
Last month out of curiosity I removed the cork plug and the little cotton ball from the phase plug of the V21 in my Leslie.
Overall the V21 still sounds like a V21 but with a brighter high treble response which is most noticeable in the high treble distortion harmonics when using the overdrive unit.
I can restore the stock mellower V21 tonality by plugging up the middle hole on the phase plug with a blob of Blu-Tak.
I also have an Eden/Hammond Suzuki 100 watt Ferro Fluid driver, and the conical shaped white plastic phase plug of the Ferro Fluid driver appears to be based on the design of the V21 phase plug shape including the middle hole on the top of the cone shaped phase plug.
I plugged up this middle hole by inserting a blob of Blu-Tac in the hole, and this resulted in a noticeable difference in the tonality of the Ferro Fluid driver by mellowing down the treble response and therefore reducing the bright harsh edginess of the sound.
Whilst the Ferro Fluid driver with the plugged up phase plug middle hole still sounds different from the V21, it does sound mellower and less harsh so therefore I do recommend this very simple modification for those who have Ferro Fluid drivers in their Leslies and they do not like the harsh edgy sound.
The attached photos here below show the Jensen V21 with the stock cork plug in the phase plug middle hole, and then with the cork plug removed exposing the little cotton ball normally hidden underneath the cork plug.
There is also a photo of a Jensen V21 in the Jensen RP201 midrange horn and there is no cork plug in the phase plug middle hole.
There is also a photo of the Ferro Fluid driver with the stock phase plug middle hole visible, and then with the middle hole plugged up with Blu-Tak in order to mellow down the treble response.
All the best.
Kon.
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