Creative use of 6J5 - UK Vintage Radio Repair and Restoration Discussion Forum

Argus25 · 8th Dec 2019, 7:10 am

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.

Radio Wrangler · 8th Dec 2019, 10:56 am

Wild!

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.

David

G6Tanuki · 8th Dec 2019, 4:31 pm

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.

8th Dec 2019, 7:10 am	#1
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	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. Attached Thumbnails

8th Dec 2019, 10:56 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Creative use of 6J5 Wild! 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. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

8th Dec 2019, 4:31 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	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.