Hiwatt DC-40 EL84 Screen observation

[Westrek]

Hiwatt DC-40 with 4-EL84 outputs. Grid bias and grounded cathodes. It has a Full/Half power switch which disconnects the cathodes on the 2 outer power tubes in Half Power mode. The switch also connects the secondary windings of the OT to reflect the proper load when just the 2 inside tubes are functioning. The outside tubes have 100 ohm screen resistors connected between pin 9 and the screen supply. The inside pair have the 100 ohm resistors connected between the plate (pin 7) and the screen supply along with the OT primary connection and Pin 9 is left open. I don't believe I've seen this arrangement before. Perhaps it's a mistake. The amp's been used for years like this. Love to hear any comments!

[The Dude]

......The inside pair have the 100 ohm resistors connected between the plate (pin 7) and the screen supply along with the OT primary connection and Pin 9 is left open. I don't believe I've seen this arrangement before. Perhaps it's a mistake. The amp's been used for years like this. Love to hear any comments!......

For clarification, are you saying the screen is not connected at all on 2 of the tubes? If so, I don't see how those tubes could work. Can you upload or link a schematic?

[Helmholtz]

A simple drawing would be clearer than a hundred words.

[The Dude]

... or even a photo if a schematic is not available.

[mhuss]

Agreed, the described screen connection makes no sense. Are you sure pin 9 is not connected at all on two tubes?

[Westrek]

I was mistaken regarding this. The power tube sockets are mounted to the chassis on this amp. Turns out the screen resistors for the center pair of tubes are mounted on the large pcb of this amp. The 100 ohm resistors that are connected to pin 7 along with the OT primary wires appear to me to make up the screen supply. Just a weird arrangement.

[Helmholtz]

I was mistaken regarding this. The power tube sockets are mounted to the chassis on this amp. Turns out the screen resistors for the center pair of tubes are mounted on the large pcb of this amp. The 100 ohm resistors that are connected to pin 7 along with the OT primary wires appear to me to make up the screen supply. Just a weird arrangement.

When the screen resistors are wired the plate (pin 7) instead of a screen supply, these tubes are wired for triode mode.