Either 484 or 485 can be used in the broadband amplifier. Since gain is controlled by adjusting bias on these tubes best they are fairly well matched. If not there can be distrotion.

A 27 is rated 2.5 volts @ 1.75 amps. 484/485 rated 3 volts @ 1.25 amps. A set of 27's can be used but draw extra current. Extra current will load down voltage so shouldn't need a dropping resistor. Be sure the power transformer doesn't get hot.

Norm

:I belive that 485's and 484's can be used in place of a 27 or the other way around. I have a sparton 101 using 585 (50) output tubes. it also uses 7 484's and a 27. The 27 is called for on the schematic, and is connected to the same filament winding as the 484's
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::::Hello! I am very excited.I am aquiring a Sparton highboy that I am 99% sure is a 301 equasonne.(not the really huge one).I don't know what power tubes it has yet but they could be 50's.I hope so because that would be really cool,I love huge tubes and you can still get them and there are some new Chinese built ones.The craftmanship on the radio is gorgeous and there are doors that open to expose the radio.Anyways what is with the #50 and#10 power tubes being so rare ?Were these only made for Sparton radios?I see that the 50's can handle something like 600 plate volts.Why were these discontinued? One more thing,if the power tubes are 182's or 183's can these be substituted with 71A's?Does anyone here own one of these radios?
::::No,I meant if you used a resistor or better yet add a 2.5 volt filament transformer to operate the 27,s and disconnecting the 3 volt winding.Thanks Ed
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:::I have a Sparton Equasonne, not sure of model number. The one I have has three chassis assemblies. The set came with Cardon (brand name) 285 tubes; the sockets are marked 285/250; a 1937 Sylvania tube manual lists the 50 as a substitute for 285. Other tubes are Cardon 484 or 483 (I do not remember). The Equasonne has a unique circuit. Although some later sets used another tube, the set I have has the antenna feeding a tuner assembly consisting of a four gang variable condenser and four coils - no tubes or other components. After this 'tuner', there are five stages of untuned RF amplication, and a detector. Beautiful solid walnut cabinet, wood dors over the radio, some hand-painted detail, and a significant amount of carved wood (not repwood). The 250 (50)tube was used briefly in other sets, such as some Grundig-Majestic and other high-end sets. Hams used it, which may explain why there are not many floating around. The 250 (50) was short-lived, as the (2)42, (2)47, and later the 6L6 soon became the tube of choice for high output audio. The 250 / 50 is a triode which can run at high plate voltage, and it is pretty finicky, and has a short life span before the filament loses emmissability. Transformer input coupling must be employed, and the tube is easily ruined - disconnecting the speaker, etc. Some Sparton Equasonne used 183 or 182 tubes; do not substitute with a 71A. And do not replace a 384 with a 27; I have seen it done - wrong filament voltage.
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