Heaters blow fuse

[jussi]

So I have built this amp: http://jussii.tk/tmp/6v6.JPG
Power supply is from "plexi 6v6" by m. huss

Currently I don't have the internal PT secondary fuses installed at all because I wan't to test only heaters first.

If I pull out all tubes and start the amp the heater voltage is 6.3V and led is glowing. If I install tubes and start the amp: led flashes and main fuse (1A) blows. I don't understand what could be the problem.

From this picture you can see how my heaters are wired and I've checked they are the same in the build: http://jussii.tk/tmp/heaters.png

Any ideas?

[R.G.]

Could be a bad tube or bad socket causing a short when a tube is inserted. Try inserting tubes one at a time. You can do this with the power on. When you find a tube that pops the fuse, either that's a bad tube or a bad socket, or possibly just the sum of the currents got big enough. So mark that socket, put in a new fuse and try another socket/tube. If more than one tube/socket location pops the fuse, it will be harder to debug.

While you're at it, look up "light bulb limiter" to save you some time and fuses.

[g1]

Are you using the same power transformer as the one in the huss drawing? If not, what current is your 6.3V winding rated for?

[jussi]

Thanks, R.G. I'll try that tomorrow.

g-one: Nope, I use this transformer: https://edcorusa.com/p/608/xpwr015
It's rated for 3.5 A

[loudthud]

Were the high voltage secondary fuses installed when the line fuse blew? If the center pin on a 6V6 power tube is missing, it's possible to insert the tube so that the heater connects the plate (pin 3) to the cathode (pin 8). Since this is a new build, it would be possible to mis-wire the socket in such a way as to cause a short when the tube is installed. Measure the resistance of point A to ground, then install the tubes. Did the resistance change? The heater of a 6V6 will measure about 7 ohms when it's cold, a 12AX7 about 40 ohms.

[jussi]

Thanks to everyone. The problem was a faulty JJ 12AX7 (new).