5e3 build problem

[Tubed]

I just finished two Hoffman 5e3's simultaneously. One is working fine. The other, on starting up, with no tubes except the rectifier, the 3 watt 22K resistor started smoking. I turned off the amp and the resistor has been discolored "burned" but still measures 22K. I cannot turn on the amp without it burning. What could be the problem?

[HotBluePlates]

The other, on starting up, with no tubes except the rectifier, the 3 watt 22K resistor started smoking. I turned off the amp and the resistor has been discolored "burned" but still measures 22K. I cannot turn on the amp without it burning. What could be the problem?

Well, something is a short-circuit on the preamp side of the 22k resistor.

Before venturing any other guess, I notice that on Hoffman's layout, there is an underboard wire running from the 2nd 16uF filter cap's negative lead to the 220k grids resistors. This is 1 turrent away from the preamp side of the 22k resistor. If you connected that wire to the 22k's turret instead of the 220k's turret, the preamp side of the 22k resistor is grounded. That puts all of the B+ across that resistor, and smokes the resistor. Guessing 300v at that point, that means the 22k resistor has to dissipate a bit over 4w; smoke but no fire.

Check that underboard wire first.

If no joy, then you would want to look at the preamp 16uF filter next. But let's see what shakes out from this.

[Tubed]

HotBluePlates you were correct. I had connected the wire to the preamp side of the 22k resistor! Thank you very much.

[supro66]

The other, on starting up, with no tubes except the rectifier, the 3 watt 22K resistor started smoking. I turned off the amp and the resistor has been discolored "burned" but still measures 22K. I cannot turn on the amp without it burning. What could be the problem?

Well, something is a short-circuit on the preamp side of the 22k resistor.

Before venturing any other guess, I notice that on Hoffman's layout, there is an underboard wire running from the 2nd 16uF filter cap's negative lead to the 220k grids resistors. This is 1 turrent away from the preamp side of the 22k resistor. If you connected that wire to the 22k's turret instead of the 220k's turret, the preamp side of the 22k resistor is grounded. That puts all of the B+ across that resistor, and smokes the resistor. Guessing 300v at that point, that means the 22k resistor has to dissipate a bit over 4w; smoke but no fire.

Check that underboard wire first.

If no joy, then you would want to look at the preamp 16uF filter next. But let's see what shakes out from this.

I see number 2 filter cap wire going to number 3 filter cap and number 3 cap is connected to ground
I see the TWO 220k resistors connected together and they are wired to ground with number 3 filter cap

[HotBluePlates]

Glad to help. I know from my own mistakes that issues in a new build are often simple wiring errors, like a wire into the underside of a wrong turret.

Hope you're enjoying the 5E3! I built one myself.