Input circuit differences 5D4 vs. 5E4A

[acorkos]

Can someone explain the differences from the input jacks to the first tube(s) in these two different versions of the Fender Tweed Super? Why no 68K resistors on the 5D4? Why is there a Hi/Lo volume/gain difference on the 2 inputs of each side of the 5D4 when it looks like they are identical?

5D4
http://www.freeinfosociety.com/media/images/1272.gif

5E4A
http://www.freeinfosociety.com/media/images/1637.gif

Thanks for your help!

[ThermionicScott]

Can someone explain the differences from the input jacks to the first tube(s) in these two different versions of the Fender Tweed Super? Why no 68K resistors on the 5D4? Why is there a Hi/Lo volume/gain difference on the 2 inputs of each side of the 5D4 when it looks like they are identical?

A lot of questions there!

The idea in the 5D4 was that each input would get its own triode so that the inputs wouldn't interact. There aren't hi/lo-gain differences in this amp, just four inputs. Grid-stoppers weren't used because RF interference didn't seem to be enough of a problem to warrant the extra parts and cost. As time went on, Fender decided they didn't want to be the amp people sometimes heard radio signals on.

The 5E4A uses a more sophisticated tone circuit that robs some gain. Fender decided to use one of the tubes for extra gain and a cathode-follower, so the decision was made to to sacrifice one of the input tubes, and make the inputs share a couple of triodes.

- Scott

[acorkos]

thanks for the explanation.

would rewiring the input jacks of the 5D4 to be like the 5E4A....68K grid stoppers, no 1Meg R on input 2...change the gain/feel/sound of the 5D4??

[ThermionicScott]

thanks for the explanation.

would rewiring the input jacks of the 5D4 to be like the 5E4A....68K grid stoppers, no 1Meg R on input 2...change the gain/feel/sound of the 5D4??

Since the inputs are already nicely separated, you could wire up your #1 inputs with a 68k grid-stopper and 1meg grid-leak resistor like you see in Fender's smaller amps, then wire the #2 inputs with a 68k grid-stopper and 68k grid-leak resistor. That accomplishes the same thing as the 5E4A inputs without having to make them "share" anything.

- Scott