http://www.freeinfosociety.com/electron ... lubman.pdf
I'm having a discussion with a friend, about how the inputs work.
Which input, the upper or the lower, will give the highest output signal?
What is the reason?
How many ohms are there between the signal and ground in each input, if only one input is used at a time.
Tommy
Need help reading this schematic
Moderators: pompeiisneaks, Colossal
Re: Need help reading this schematic
The top input (J3) gives a 68K/68K voltage divider to the tube grid, the bottom input (J4) sees 1 Meg to ground with a 34K grid stopper, so the bottom input is the high input (J4).
If you plug into the top input (J3) the switch on it is opened up, so only the 68K (R5) is between the input signal and the point it joins the other 68K (R7) before the grid. This second 68K's (R7) other end is switched directly to ground by the other unused input (J4) switch on the jack, so a voltage divider of 68K/68K results.
If the lower input is used (J4), the switch to ground on it is opened, so the signal goes right to the junction of the 1meg (R9) and 68K(R7). The signal also goes directly to the input of the other 68K (R5) via that J3 jack switch, so both 68K's end up in parallel with each other, which forms a 34K grid stopper to the tube grid. So you get 1meg to ground with a 34K grid stopper before the grid with the J4 lower jack.
If you plug into the top input (J3) the switch on it is opened up, so only the 68K (R5) is between the input signal and the point it joins the other 68K (R7) before the grid. This second 68K's (R7) other end is switched directly to ground by the other unused input (J4) switch on the jack, so a voltage divider of 68K/68K results.
If the lower input is used (J4), the switch to ground on it is opened, so the signal goes right to the junction of the 1meg (R9) and 68K(R7). The signal also goes directly to the input of the other 68K (R5) via that J3 jack switch, so both 68K's end up in parallel with each other, which forms a 34K grid stopper to the tube grid. So you get 1meg to ground with a 34K grid stopper before the grid with the J4 lower jack.
Re: Need help reading this schematic
That's just how I see it.
That's why I think that it would work to use only one input, with a 68K and a 1M to grund after it, and then have a 68K that can be switched either in paralell with the other 68K or grouned, to form the 68/68 divider. The switchable 68K would of course have to be switched on the input side.
Tommy
That's why I think that it would work to use only one input, with a 68K and a 1M to grund after it, and then have a 68K that can be switched either in paralell with the other 68K or grouned, to form the 68/68 divider. The switchable 68K would of course have to be switched on the input side.
Tommy