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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 8th Dec 2019, 7:10 am   #1
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Default Creative use of 6J5

A member was looking for a 6J5.

Every time I think of a 6J5 valve, I think of the Philco 38-7 pre WW2 radio. One of the most creative, futuristic and advanced MW/SW radios the world has ever seen, not only the industrial design of the cabinet but the circuitry and chassis construction.

They ingeniously used a 6J5 as the detector and created one of the world's first examples of a delayed AGC with it.

If that wasn't enough, have a look at the coil on the IF transformer that was placed in the 6k7's suppressor connection (bet you have never seen that before) I won't spoil it by telling you what it does and, if that wasn't enough they used fixed bias for the audio stages and also had "cone centric" tuning. They were way ahead of the curve in radio development at that time in history.
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Old 8th Dec 2019, 10:56 am   #2
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Default Re: Creative use of 6J5


Interesting that the -ve bias point goes in to the O/P stage grid sans any decoupling. Must be using a very big grid leak resistor or suffering added hum.

Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
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Old 8th Dec 2019, 4:31 pm   #3
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Default Re: Creative use of 6J5

The "IF coil feeding the suppressor grid" is something I've seen before in some 1930s US radios - sometimes called a "triple-grid amplifier" I believe it was invented as a way to get round some of the early patents on the 'classic' grounded-suppressor-pentode circuit.
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