5E3 Interactive Volume Controls

[rrputnam]

A friend of mine loaned me his 1959 Tweed Deluxe and I fell in love with the interactive tone controls. I recently finished a 5E3 build using a Hoffman board layout. While I like the tone of the amp, the volume controls are not particularly interactive. Does anyone have an idea what I might have done wrong that would result in a lack of interactivity?

Thanks in advance.

Rob

[loudthud]

The original 5E3 had a common cathode resistor on the first preamp tube. Pins 3 and 8 connected together and an 820 ohm resistor to ground bypassed by a capacitor. Some people like to use independent resistors on each pin with different capacitors for a slightly different voice.

[stokes]

Splitting the cathodes on the first stage doesnt affect the volume controls,I've done it on both my clones and the original,had no problems with the volume controls.I'm not familiar with the Hoffman kit,but I would compare that to the original schem and see if there is some difference.

[Bruce / Mission Amps]

Splitting the cathodes on the first stage doesnt affect the volume controls,I've done it on both my clones and the original, ...

Sure it does.
Both volume pots are in parallel and after their triodes respective coupling caps. There for the two 12AY7 stages are free running with respect to where the wiper is set to the volume pot.
Because the two triodes are sharing the same cathode resistor and cap, the unused triode (channel) becomes "weakly" cathode driven and if you plug into and play into one channel with it's volume off, you can turn up the other one and get about 2-3 watts of power out of the amp.
Splitting the cathodes eliminates that effect.
However, the volume pots are still in parallel so one volume pot setting can still attenuate the other when turned way up.
With the unused volume up at around 9 to 12 you can now turn the used channel up much further then before because the signal is leaking around the other channel's volume pot, to the plate's 100nF coupling cap of the unused triode and subsequently sucked to ground through it's 100K plate load resistor to the 16uF to 22uF filter cap.
Any time you have a capacitor and a resistor with one of them grounded it acts like a filter or tone control.
If the cap is big enough and the resistance small enough it sends all the frequencies to ground... of course the total impedance is higher in the actual amp then the preamp stage you actually want to hear so it merely attenuates the signal to some degree.

[stokes]

"Because the two triodes are sharing the same cathode resistor and cap, the unused triode (channel) becomes "weakly" cathode driven and if you plug into and play into one channel with it's volume off, you can turn up the other one and get about 2-3 watts of power out of the amp.
Splitting the cathodes eliminates that effect."
Okay,splitting the cathodes will eleiminate that effect,but the two volume controls are still interactive and just like the stock single cathode resistor set-up,turning the unused volume control still "scoops" the mids and wont adversley affect the interactivity as the original post seems to be describing.