Hiwatt DR103 blowing fuse

[Oddvar R]

That's great, thanks.

[Oddvar R]

I had to get up to 8k, (didn't have 7k) and it went down (or up) to minus 38.9. Can't test it now, it's abou midnight now, but at least there was ampnoise in the speaker. That was a great tip, thanks.

[sluckey]

-38V is what's shown on the schematic.

[Oddvar R]

So, I am stilling troubleshooting the Hiwatt build. My worst case untill this point-

I wonder a bit about the voltage on pin 4 and 6 on the PT tubes. I have about 478 on both sides. Is that as should be or are the resistors blown?

The grounding on the picture, is it going via the 10n cap?

[martin manning]

Pin 6 is only used as a tie point to support the 100R resistor connected to pin 4 (the screen pin). I would not expect to see any voltage drop across that resistor with the tubes removed, and less than one volt when they are installed.

The 10n cap is part of the negative feedback loop. It is grounded with the preamp filter stack, pins 1 and 8 on the left-most power tube, and the 100u cap and 47k resistor in the bias supply.

[Oddvar R]

I seem to have gotten a bit further into the fault line. What could be the cause of this? Never seen that before, V1 12ax7?

[martin manning]

The white getter says indicates it has lost its vacuum. The envelope is obviously cracked now, but it could have developed a leak at one of the pins.

[Oddvar R]

This is the second tube that ends up this way. What could cause it? Must have gotten a great push.

[Oddvar R]

I am now trying to/ starting a possible rebuild of my Hiwatt DR103, which I never seem to be able to finish, using the Tube Town layout. In the enclose they have omitted the par circled in pink. Why is that I wonder. Something to do with the bias routed to a PCB? Or?

[mhuss]

That's where the series voltage dropping resistors normally go (between the can caps).