GSG problem

[rick90405]

Hello everyone!
First time posting, I just built a GSG 6b4g.
first try, the rectifier tube turned bright orange with purple haze....
tried 3 tubes, same results.
So I checked the volages for the 6ax5gt
Pins 2 and 7 4.3v
Pins 3 and 5 344v
Pin 8 is not connected to anything, though the voltage check up list wants it at 333v, I got wild swings and had to cut power as the tube was loudly complaining ( on the kitchen table not hooked to anyting)
What could be wrong?
Richard

 

[djn]

Best to start tracing the wiring with a very open mind. I built a phono pre once that was red plating only one of the tubes. I traced that amp for a week and could not find the problem.....because.....I assumed I did everything right. A friend came over and took a minute to see that I had the B+ hooked up to one of the heaters on the tube.

 

[rick90405]

Thanks, I am new at this.
I wired the amp following pix posted on line, so I will trace what comes out of the Tx and where it goes.
Richard

 

[DF96]

Pin 8 (cathode) should normally be connected to the first PSU cap, +ve side. Have you grounded pin 8 instead, or got the cap the wrong way round? The orange anode and lowish heater voltage suggests an overload. If you left it like that it would be a race between the 6AX5 and the transformer to see which one blinks first and lets out the blue smoke.

 

[rick90405]

Thanks, all caps are properly installed, I will remove the board and see if there is a trace from pin 8 on the other side.
Will let you know

 

[rick90405]

Pin 8 is connected to nothing at all !!

 

[DF96]

Are you counting the pins the right way?

 

[7N7]

Best to start tracing the wiring with a very open mind. I built a phono pre once that was red plating only one of the tubes. I traced that amp for a week and could not find the problem.....because.....I assumed I did everything right. A friend came over and took a minute to see that I had the B+ hooked up to one of the heaters on the tube.

I know what you mean: I recall an E88CC that survived with 300V on one of its grids... Today a screwdriver slipped and the red LED on a cascode CCS went out. I removed the board, replaced everything and it refused to behave - sinking too much current. Finally I gave up. ignored the calculations and removed a 150-ohm resistor and replaced it with a 220 ohm one. Perfect. Funny, the other board which is absolutely identical still has its 150-ohm resistor and works perfectly and to spec.
Sometimes you have to give up!

Paul

 

[rick90405]

Pins are numbered, and the socket is soldered in the proper direction.
I tested the 180 ohm resistor at R17 a and b and read 90 ohms on each, is that normal?
Another board is comming in the mail, maybe 2 is the charm....

 

[rick90405]

Hooray!
I went over the schematic, and decided to ground the board from J6 to chassis and IEC plug.
It is working fine now, but I stay close.
On most pix I saw no one grounding the board.
Thanks for your support