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Old 1st Dec 2021, 9:43 pm   #1
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 7,356
Default Saving sets from butchery

Hi Folks, for some time now there have been a number of "antique" dealers and Steam Punk fans who would take an old valve radio, rip the guts out and fit a module or Bluetooth device to allow music to be played over the speaker in the set.
Direct connection, even when PU sockets are fitted will often not work as there is insufficient signal to drive the amp to sufficient volume.
A little design work has come up with a modern version of the "intervalve" transformer shown below. This is wound for a 4:1 ratio and gives sufficient volume for most sets and allows the set to be both used as intended and as a means of playing music from your phone.

Note that while it provides isolation it is NOT intended to be used on AC/DC sets with live chassis such as a DAC90/a; a totally different design would be needed for that application.

In use the signal from the phone is fed into the primary of the transformer, the secondary is connected across the volume control pot. This small transformer can then easily be mounted in the rear of the set.

Enjoy your digital music !

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