Issue With Bassman 5F6A Build

[Guitarnut]

And the other side of the 10k is ~14.25k to ground, and the cathodes of the PI are ~14.7k?

I think you're on to something. The cathodes are open. The junction of the 1m, 1m, 10K and 470 is 14.25K. The other side of the 470 is 0. If I meter the junction side of the 470, I get nothing unless I press it firmly against the turret...another bad solder joint.

We're gonna get this, I just know it.

I'll report back in a few...

Peace,
Mark

[CHIP]

I can't tell for sure by your pictures ,but on your PI socket there looks like there maybe a solder bead between pin 2 and pin 3.

[Guitarnut]

I can't tell for sure by your pictures ,but on your PI socket there looks like there maybe a solder bead between pin 2 and pin 3.

I've looked it over but I'll double check. Thanks!

Peace,
Mark

[Guitarnut]

And the other side of the 10k is ~14.25k to ground, and the cathodes of the PI are ~14.7k?

I pulled a few caps and got in and cleaned it out and started over on the junction turret. I now 14.75K on the cathodes!!!

I'm going to power up and check the PI before I deal with the inputs.

Peace,
Mark

[Guitarnut]

New PI numbers. I have 412v on pin 6, 250v on pin 1 and 33.2v on the cathodes. And, a nice little hum in the speakers that I haven't heard before. It goes away when I touch the outside of the input jacks.

Is pin 6 still a bit high?

Peace,
Mark

[martin manning]

There's still or another janky joint there somewhere.

[Guitarnut]

There's still or another janky joint there somewhere.

Okay...more investigation tomorrow.

Thanks again,
Mark

[martin manning]

Measure resistance from the grid pins (2 and 7) to ground and see if you get ~1014k.

[Guitarnut]

1029K on 2 and 1016K on 7.

[martin manning]

Ok how about resistance from pins 1 and 6 to the junction of the 100k and 82k resistors?

[Guitarnut]

Ok how about resistance from pins 1 and 6 to the junction of the 100k and 82k resistors?

97.5K on 6 and 79K on 1.

Gotta run to work. More this evening.

Thanks again,
Mark

[martin manning]

So the resistances along the intended current paths are looking good. Try measuring the resistance from the PI grids (2 and 6) to ground to see if there is much difference. Seems like there must be some un-intended path on the side with the high plate voltage.

[Firestorm]

Maybe try reflowing the solder on V3 Pin 8. Probably wouldn't hurt to touch up everything that doesn't look nice and solid.

[Guitarnut]

So the resistances along the intended current paths are looking good. Try measuring the resistance from the PI grids (2 and 6) to ground to see if there is much difference. Seems like there must be some un-intended path on the side with the high plate voltage.

I'm guessing you meant 2 and 7...no change from the last time we checked them.

1029K on 2 and 1016K on 7.

[martin manning]

Yes, 2 and 7, the grids, but resistance to ground.