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Re: Victor Electrodynamic Driver Impedance
Posted: Sun Nov 18, 2018 9:39 am
by Uncle Vanya
Governor Flyball wrote:Have a look on the schematic to ensure that the field choke coil is not in the negative leg of the power supply. The common design in those days was to use the dc resistance to generate a negative voltage drop which was used to bias the output tubes. If the DC resistance is too low you may end up with insufficient bias which will stress the output tubes.
On the AP-947, AP-951 and AP-997, units which were designed to be used with dynamic loudspeakers, the field coil is connected in the HT lead between two 4MFD condensers in the usual π filter arrangement. The RPA 1, which was used in the Borgia II, Hyperion, and other machines which were originally fitted with magnetic drivers places the field connections accross the 90 volt B supply. In these sets the field performs no filter function and may be entirely dispensed with.
Re: Victor Electrodynamic Driver Impedance
Posted: Mon Mar 11, 2019 1:15 pm
by startgroove
Does anyone have a picture of this driver. I'm trying to confirm if I have the correct one, and if it is complete. Cheers, Russie
Re: Victor Electrodynamic Driver Impedance
Posted: Mon Mar 11, 2019 1:39 pm
by Victrola-Monkey
Russie,
This driver can be seen in photos I posted here:
http://forum.talkingmachine.info/viewto ... 25e687d2b3
Re: Victor Electrodynamic Driver Impedance
Posted: Mon Mar 11, 2019 6:30 pm
by startgroove
Thank you for that info. I'm having a bit of a problem understanding which is the driver parts, and what is not. I found this (below) driver which I thought was part of our Borgia, but it does not seem complete. Can you tell me what is missing, or if it is even the right one? Cheers, Russie
Re: Victor Electrodynamic Driver Impedance
Posted: Mon Mar 11, 2019 6:39 pm
by Uncle Vanya
That appears to be a Thorola balanced armature driver. It is the rough equivalent of the drivers made by the Radio Corporation for Victor and Brunswick, or of the Baldwin and Utah drivers save that it is made of particularly awful pot metal. I've probably had fifteen Thorola horns over the past couple of decades none of which have had salvageable drivers.
Re: Victor Electrodynamic Driver Impedance
Posted: Mon Mar 11, 2019 6:45 pm
by Victrola-Monkey
Here’s a photo I got from another TMF member that did some work to his VTMC/RCA dynamic electromagnetic driver.
Re: Victor Electrodynamic Driver Impedance
Posted: Mon Mar 11, 2019 8:25 pm
by startgroove
Fantastic! You guys are so very helpful! I've been trying to solve this one for a couple of years now. Thank you, thank you, thank you, Victrola-Monkey and Uncle Vanya. Cheerio, Russie
Re: Victor Electrodynamic Driver Impedance
Posted: Thu Mar 21, 2019 10:58 pm
by MarkELynch
A very interesting discussion! Wayne, you got that driver picture from me a while back, I’m glad you posted it.
BTW, Victor referred to the driver as the “Intermediate Speaker”
Here is a link to the internals of the driver. Notice the shape of the aluminum diaphragm and the way the voice coil is attached.
https://www.dropbox.com/sh/n0ms4pn2uj6s ... 9w4pa?dl=0
Mark