Show Posts
496
General Radio Discussion / Re: Troubleshooting (or just shooting) a Johnson Valiant
« on: November 21, 2014, 0133 UTC »
Guys, this is on the low-voltage side, protected by the 1.6 amp fuse, which is the one blowing. At the time, there was no smoke, no drama whatsoever, just "phhhht" went the slow-blow low-voltage fuse, after full tune up. I even checked the wrong fuses first, since that thing had never gone out on me. The 8-amp fuses covering the high voltage side never blew when it broke down.
This happens about 7-8 seconds after turning on the filament switch. In that amount of time I would normally see the meter showing oscillator drive, but now there's nothing.
The solid state diodes supplying the high voltage don't come into play until you throw the plate/high voltage switch. I've had those go out before. Since there's no drive, I never get to the point where I'd be throwing that switch.
I've since found that the 5763 multiplier/buffer tube is dead, (also on the low-voltage side), but the oscillator should normally work without it (as it did in Valiant #2 which I had traded all the tubes with). I will check/clean up that tube socket, as well as all the others with some DeOxit and see what happens... I've been checking other parts for shorts but haven't found anything.
It does seem to me that there's a short somewhere, probably on the low voltage side, but I suppose a filament short on the other tubes could do it also.
Don't own a Variac, that's something I never picked up. What I did pick up were spare T-1 power and modulation transformers.... but I don't think those have anything to do with this.
This happens about 7-8 seconds after turning on the filament switch. In that amount of time I would normally see the meter showing oscillator drive, but now there's nothing.
The solid state diodes supplying the high voltage don't come into play until you throw the plate/high voltage switch. I've had those go out before. Since there's no drive, I never get to the point where I'd be throwing that switch.
I've since found that the 5763 multiplier/buffer tube is dead, (also on the low-voltage side), but the oscillator should normally work without it (as it did in Valiant #2 which I had traded all the tubes with). I will check/clean up that tube socket, as well as all the others with some DeOxit and see what happens... I've been checking other parts for shorts but haven't found anything.
It does seem to me that there's a short somewhere, probably on the low voltage side, but I suppose a filament short on the other tubes could do it also.
Don't own a Variac, that's something I never picked up. What I did pick up were spare T-1 power and modulation transformers.... but I don't think those have anything to do with this.
