More Express build Questions

[sliberty]

1. There are 3 diodes connected from pin 3 to pin 8 on each power tube on the schedmatic (Kelly 90). On the layout, these diodes go from pin 3 to pin 1, and pin 1 is then connected to pin 8. Now I know that a 6V6 has no internal connection on pin 1, so using it as a connection point seems harmless enough for 6V6's, but on an EL34, pin 1 is Grid #3. So we are gounding Grid #3 - is that kosher? Maybe it would be better to just run the diodes from pin 3 to pin 8 and not involve pin 1???? [I am certainly not questioning Ken's wisdom, just trying to learn)

2. Each power tube has its own chassis ground lug. Is it important to keep these seperate? It just turns out that in my chassis, it would be easier to bring these grounds to the same lug.

More to come, I'm sure.

Thanks,
Steve

[Elcabong]

1. There are 3 diodes connected from pin 3 to pin 8 on each power tube on the schedmatic (Kelly 90). On the layout, these diodes go from pin 3 to pin 1, and pin 1 is then connected to pin 8. Now I know that a 6V6 has no internal connection on pin 1, so using it as a connection point seems harmless enough for 6V6's, but on an EL34, pin 1 is Grid #3. So we are gounding Grid #3 - is that kosher? Maybe it would be better to just run the diodes from pin 3 to pin 8 and not involve pin 1???? [I am certainly not questioning Ken's wisdom, just trying to learn)

This is very common to ground the suppressor grid with EL34 like this. Some builders like Traynor connected it to a negative supply, supposedly improving efficiency and reliability. This is discussed on here http://www.tone-lizard.com/Marshall_Myths.htm

Regarding where the diodes are grounded, I do not think it matters as this is a safety feature and no current goes through them in normal use.

2. Each power tube has its own chassis ground lug. Is it important to keep these seperate? It just turns out that in my chassis, it would be easier to bring these grounds to the same lug.

I do not think it makes a difference ( but hey, I am not Ken ). In the Komet pictures and in my Express built, which by the way is not a "true" Francesca clone, the tube grounds are connected to the same lug. As an added feature, each branch has a 1 ohm resistor for bias measurement before going to the common ground.

Gilles

[Allynmey]

My understanding is that it protects your OT from "transients" as he called them and "Flyback" due to tube failure.

Allyn


I used them on my build.