Dual tube for M4 changer - Printable Version

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+--- Thread: Dual tube for M4 changer (/showthread.php?tid=14757)

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Dual tube for M4 changer - clockman1954 - 06-09-2016

Can you tell me which tube is the dual tube for the radio / phono in a 48-1270 console with M4 changer?  I had it replaced this year, but it seems to have blown again.  The radio was rebuilt last year and the cartridge was done this year.  What might have caused it to fail so soon?

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RE: Dual tube for M4 changer - Radioroslyn - 06-10-2016

Well there's only 5 dual section tubes in your set. Can you narrow it down a bit???

terry

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RE: Dual tube for M4 changer - clockman1954 - 06-12-2016

I need to know which tube switches from radio to phono when you push the button on the console.

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RE: Dual tube for M4 changer - Radioroslyn - 06-13-2016

Well the actual switching is done by the radio/phono switch of course. The amplifier stages are on all the time they just are amplifying what ever signal is being sent to it. The on line schematics are awful for this set!!! But it's either the 7F7 or the 7AF7. They call the 7AF7 the "phono amp". The 7F7 maybe used for tone compensation but it's hard to tell.

Terry

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RE: Dual tube for M4 changer - clockman1954 - 06-13-2016

Thanks, I found my old Photofact from the repairman and it says 7AF7 is the Phono Amp tube and 7F7 is for the "AF Amp", but I don't know what that is (AM band?).  Thanks again, Chris.

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RE: Dual tube for M4 changer - Radioroslyn - 06-13-2016

AF amp is just a generic term for audio frequency amplifier. So is the 6SQ7 for that matter.
 Terry

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