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: : : : : : : : : : : :Sir Jim. . . . . : : :Right-o . . . that use of the field coil magnet of a lesser dynamic speaker . . . . sans . . . its extracted BULKY cone basket metal works should work fine on voltage drop and filtering, if being of about the same Z and resistance as the initially subbed in "huge" electrodynamic test speaker. . : : :Then . . .the last question first . . . if you are wanting to see what olde tyme metering readings were . . . merely sub in a resistor to equate the same value as the desired meter sensitivity ACROSS your DVM test leads. :Easily done if you use a set of Pomona in and out bannana or pin jacks, with the resistor connected between the two terminals. . . . . E.G . . . . or just plain use your electro / mechanical ingenuity. : : : : : : : : : : :Then, you opt whether you want the 1000, 5000 ohms per volt value by making the resistor agree with the FULL voltage on a particular voltage range scale. : : :Or you can even step on up to the more modern Tripletts and Simpsons with their 20,000 ohms per volt sensitivities. : : : :Now . . . Ye olde detector circuit . . . a . . la . . .112: : : : : :The strong 175 khz IF signal comes in from the Item 37 IF tranformer and passes up to the '27 detector grid which is acting as the anode of a diode detector, while having its plate and cathode co-joined and combinationally functioning as a single cathode of a diode detector. :Now look down at power supply feed point E, which is originating down at the HV centertap of the HV winding of the power transformer and then traveling over to the two series sections of Item 58 resistor. : : :Those two resistors are holding the HV centertap from going directly to ground . . . to the right of the right 58 section. : : :Thereby two negative voltages levels are being developed across the R58's 2 nodes, with the "D" node having the greater voltage to be able to provide 1st grid biasing for your '45 AF outputs. : : :The lessor voltage referenced "E" node is feeding up via item 64 resistor and finally up to the '27 cathode. : : :This biasing counteracts the contact potential of the diode detector circuit and makes it a bit more sensitive of low signal input. The Item 40 capacitor passes off lower frequencies and further filters the negative supply . :This low level negative biasing voltage also gets coupled into the AVC circuitry via the item 70 of an items 39/70 voltage divider bridge. :Now as when compared to the AVC being returned to ground . . .versus this additional negative voltage being inserted at its low end instead, there is now an overall greater AVC dynamic range swing being created . : : :The bottom of the Item 37 IF transformer is just bristling with 175,000 little pinpoints per second of RF +&- going wavelets which are outerly conforming to the AF waveshape of that radios AM audio signal. : : :Well all of the +going nodes rushed up the grid of the '27 and escaped to ground . . .but . . Katy bar the door ! . . . cause all of the negative nodes are flying out the bottom end of the IF transformer and initially meet with Item 38, cap, whiich strips off and passes all of the RF and the very-very highest frequency audio to ground. :The developed negative DC voltage and detected audio ac components are then meet with the Item 39/70 voltage divider arrangement which feeds a reduced - AVC voltage thru Item 34 up the 1st grid circuitry of the '24, 1st IF amp. : : :(Additionally the '24 2nd IF amp is having its gain throttled back a bit by the application of the fixed full "E" voltage, being tied into its 1st grid circuitry.) : : :Now the last aspect of the output coming out of the bottom of the Item 37 IF transformer is its feeding directly down and past its item 39 tie in and then go below that node to proceed to the left where the full developed -AVC level is passed thru resistor Items 68 and 8, with some intermediate low frequency filtering / decoupling /time delay constant being provided by Item 67, until the AVC ends up at the 1st grid of the frontal RF '24. : : :Previously,we just took the left path, way down from the IF transformer, now . . .going along the right path would have us going into that item 41 which is receiving the detected audio component for initial audio preamplification. : : :That should cover the sets detector function, along with its conjunct AVC and the initial audio processing. : : : : : : : :73's de Edd : : : :

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::Hi Edd,
::Thank you for your reply, I can now see what the purpose of the coil is. I salvaged a field coil off of an old junk speaker and it seems to work well.
::Two other requests if you don't mind.
::First; I am trying to wrap my head around the detector circuit in this set and I am not sure I quite understand how it is supposed to work. I am hoping you can explain how it works?
:: Also, the voltage readings that I get, using my high impedance digital meter, are of course much higher than the voltage chart published with the schematic which I realize was determined with a low impedance voltmeter of the day. Is there a factor that can be applied to determine what today's voltmeters should read?
::Thanks in advance.
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::Jim
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::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: :::Sir Jim. . . . . ::: ::: ::: :::Au contraire . . . . on that set of yours . . where one typically would expect to see the field coil of a dynamic speaker being used in the circuitry position where you can see the Item 63 filter choke being used for the "C" B+ supply buss of the receiver. ::: ::: :::Note that "C" lines B+ ends up at the center tap of the power output transformer and then flows down through your speakers field coil and then flows out of it into a power resistor going to ground. ::: ::: :::That dual combination constitutes a voltage divider bridge to create a lower B+ voltage which then grabs a little more filtering via the Item 49 filter capacitor and then it flows on its way up the buss which feeds its then created voltage to priovide for the plate supply voltages of your two '27 AF tubes and THE plate and screens of all of your frontal RF tubes. ::: ::: :::I personally would use the primary of an old AF output transformer to fill in for that function, or lesser, a power resistor of proper ohmmage and wattage, to create a like sub supply voltage level could be used. ::: ::: :::Take due consideraton that a bit more filtering cap value might be required in replacent of the more effective inductive filtering previously available. . . . . if subbing in a resistor replacement. ::: ::: ::: ::: ::: ::: ::: :::73's de Edd ::: ::: ::: :::

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::::Hi All,
:::: I am finishing a Philco 112 restoration. The chassis has been recapped etc. and plays beautifully through a 12" speaker from another Philco (40-185)that I had in the shop as the radio itself did not come with a speaker.
:::: Unfortunately the 12" speaker is too large for the cabinet so I have ordered a 10" (correct size) but has a permanent magnet.
:::: My question is about the power supply on this set. It appears to me that the speaker magnet is not a part of the power supply filter?
:::: If it isn't, is there any need to sub a resistor or choke in its place?
:::: Thanks in advance,
::::Jim
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