Trainflex input stages

[Elcabong]

To Ross or whoever has a copy of the Trainflex schematic.

I am confused by the way the inputs are connected in the Trainflex schematic. The first option show a single/parallel arrangement where the two 100K plates resistors are connected together, effectively corresponding to a 50k load. Should it be a single 100k there?

In the alternate input structure, you can use either an Express or a Komet input stage. In this case, how can it be connected to the next stage? Using mixing resitors before the tone stack?

Thanks,

See the Trainflex 1.0 schematic here http://pages.videotron.com/chigbl/Trainflex1.jpg

[RossH]

The first option show a single/parallel arrangement where the two 100K plates resistors are connected together, effectively corresponding to a 50k load. Should it be a single 100k there?

No, when you parallel a tube you double the capacitance and divide the resistance by two. It has also been said that paralleling the first stage will lower the noise floor and fatten up the sound some. It is what I did to mine but I have never A/B'd them. Some have reported not liking it that way. On my new build I am leaving it single. The input stage gives you the option to run it either way. If you were going to run them in a permanently parallel arrangement and stick to the schematic values you would have 56k plate, 820 cathode and 50uf cathode cap.

In the alternate input structure, you can use either an Express or a Komet input stage. In this case, how can it be connected to the next stage? Using mixing resitors before the tone stack?

Just connect the plates together and link them to the tone stack. If you want to use mixing resistors you can. It will probably just tame the high end a bit. Are you planning to use both channels simultaneously?

HTH,
Ross

[Elcabong]

Thanks for answering.

No, I do not plan to use the channels simultaneously. I liked the idea to do something with the unused half of the tube and I am currently implementing the single/parallel configuration ( still on paper, doing the layout ). It is flexible and can be modified to the alternate input later if I am not happy with it.

Gilles