i just bought a model 84 to rehab. dirty but in pretty nice shape. except for the speaker cone which is badly torn. i plan to use a modern speaker and wonder if anybody knows of or could recommend one that i could "hide" inside the metal frame of the original.
i used the word "rehab" because i don't intend to completely restore this 2-knob 84 but would like to retain the original appearance. for example, i'll clean and leave the original metal cap cans but just mount modern caps out of sight below the chassis.
I put a six inch, full range hi fi speaker inside an RCA 100 metal surround. Works great. I used a round piece of 3/8 inch plywood for a baffle with a strip of Insulating foam around the edge.
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i also have an 84b. imho i think it best to send it out and have it reconed.make sure you get a paper cone. foam surrounds that ive seen will stand proud of the frame. this will require you to somehow build a spacer to keep the surround from hitting grille cloth frame. failing to do so will muffle the speaker. as to your modern speaker conversion you will need to consider the electromagnet thats on the speaker. you cant just remove it. its other job is to act as a power supply choke. if you do you will need to add one and theres very little room on the chassis for it . or add a power resistor and increase the power supply capacitance values. lastly you will need a speaker transformer for your new speaker which is 4-8 ohm i presume. the original drives a .89 ohm voice coil. again you got to put that stuff somewhere. those metal cans arent capacitors they are covers for the antenna transformer and if transformer. if your radio is original there will be a cardboard tube thats a dual capacitor. this isnt a very sophisticated radio. they are remarkable to me as theres so little in them and for what they are they do it pretty well. but the fact is they were a low price range radio for the masses that could afford it due to the depression.
nice try falcon123, but i don't think an 84 is worth the cost of a full restoration, including a recone of the speaker and a new dial face at the least for this one. that said, the cabinet is in exceptionally good condition. no damage whatsoever [in case someone is interested].
but now i'm interested in knowing just how critical the speaker impedance is. would i even notice a difference in sound quality with a modern 4 ohm speaker? at my age, that is
. and if it is an issue, could i fake it by just putting a resistor in parallel with the speaker?
then, speaking of the impedance, is a simple resistance reading anywhere close? and if not, at what frequency should i calculate the impedance? from the inductance, which i find by setting up a tank circuit. i "ping" the circuit thru a diode at a low frequency, read off the resonant frequency on an oscilloscope and compute the inductance.
The 84 uses a voice coil that is 1 ohm @ 400cy.
file:///C:/Users/JOHN/Downloads/Screenshot_2020-09-24%20Philco%20Quality%20Radio%20Parts%201936%20pdf.png this is from the 1936 philco parts catalog. i cant figure out how to make this visible! but the 1936 catalog clearly shows 36-1073 speaker for a 84b with a .89 0hm @ 400 hz voice coil