hello, im trying to fix a motorboating on a crosley o2ca radio. the radio works good for 30 secs then starts to motorboat. the radio does not have original power suplly and two of the 6j5 tubes are gt instead of metal i replaced all caps . thank you for any info

First try substituting metal tubes for the glass ones. If you do not have any at hand, wrap the glass tubes with foil and touch the foil to the chassis. Do not allow the foil to touch the tube pins.

Thomas

:First try substituting metal tubes for the glass ones. If you do not have any at hand, wrap the glass tubes with foil and touch the foil to the chassis. Do not allow the foil to touch the tube pins.
:ok i will try the tubes thank you
:Thomas

Assuming that you changed filter caps and paper caps, just checking for a cold solder joint, a stray solder blob, or wired a cap connected to the wrong pin or even wires routed a little too closely even can be a cause. I may be repeating what you already have done, I am just reciting what I normally check if I encounter something out of the ordinary, and I have actually found on a couple occaisions a faulty filter cap that was factory fresh (rarely do I try to salvage old caps for filters).

And with all that said, a couple other things to check are the grid resistors for the 6AC5's It is possible that they have shifted enough in value to be one cause. According to the schematic, they should be from pin 5 to ground on each 6AC5 and should be 33K ohms. Also check the grid load resistors on both 6J5's, they should be 330K ohms.

::First try substituting metal tubes for the glass ones. If you do not have any at hand, wrap the glass tubes with foil and touch the foil to the chassis. Do not allow the foil to touch the tube pins.
::ok i will try the tubes thank you
::Thomas