grid of 78 tube to sig gen,6j8g grid to signal generator. somewhere saw an adaptor socket that could be used, to save removing radio from cabinet. think it was a philco part #. Does any one know how to make on or have 1 for sale? Got radio working but too week and mystery must be within 3 4 feet to work. Thsnks Bill
Both the 78 and the 6J8 have grid caps on the top of tube- there is no need to remove the tube to inject a signal. Try using the lead of a .05mfd cap wrapped around the tube grid post and the other end of the cap to the sig gen. The value of the cap isn't critical but .01- to .05mfd is a good range. It's a good practice to leave the actual grid clip disconnected when injecting a signal.
Pete, this is great news! Should I use an isolation transformer or is it not needed with this radio. Thanks, Bill