Divided by 13 9/15 schematic?

[dayn]

Has anyone here mapped out the Divided by 13 9/15 amp schematic? I'm especially interested in the dual 5879 preamp section tolearn what they are doing there.

[dayn]

Still looking, in case this catches the eye of someone with info, thanks!

[jbrrrrr]

No schematic to offer you, but out of my own curiosity, I looked up the JRC 9/15 to get a sense of how it's laid out, and found this description on Doug's Tubes:

"Starting from right to left, the single input of the amplifier (high and low sensitivity) feeds the inputs of two 5879 Pentodes, each with its own volume control and blendable. Each is voiced differently: one is brighter with more clean headroom while the other has more gain and is thicker in the low mids. Added to this volume is a 6 position switch which offers a "bright cap" selection. The last knob is a high cut for the overall amplifier. The "Mode" toggle provides a selection of either 9+ Watts with 6V6s, or 15+ Watts with EL84s, offering and exceeding the best tones available in some of our favorite late 50's American 6V6 amplifiers, and our favorite EL84/EL34 English amplifiers."

- Two inputs, each gets its own 5879 tube
- One is biased bright and clean, the other is biased gainier and with more low mid emphasis (probably coupling cap values and cathode bypass resistor + general bias point differences)

If you look at the Bassman 6G6A schematic I attached, you can see an example how how two channels with different preamp tubes and mixed later in the circuit are commonly arranged - the difference here would be that it would be just one pair of hi/lo inputs that split off to the two different stages - basically jumpered internally.

Here's also a schem for the FTR37 which might give you a clue about how that rotary tone stack is put together - the 9/15 is worded like it's just selecting different bright cap values to shift how low the corner frequency extends down into the upper midrange. This FTR37 schematic selects different coupling caps after the first stage that target the low end/low mids, but the general idea would be the same, just located around where the bright cap is implemented.

As far as the 6V6 vs. EL84 switching - they're both cathode biased sections so I don't see anything particularly tricky happening there - just a clever switch to select which output tube section is in circuit that manages to avoid any major noise or disturbance.

[dayn]

No schematic to offer you, but out of my own curiosity, I looked up the JRC 9/15 to get a sense of how it's laid out, and found this description on Doug's Tubes:

"Starting from right to left, the single input of the amplifier (high and low sensitivity) feeds the inputs of two 5879 Pentodes, each with its own volume control and blendable. Each is voiced differently: one is brighter with more clean headroom while the other has more gain and is thicker in the low mids. Added to this volume is a 6 position switch which offers a "bright cap" selection. The last knob is a high cut for the overall amplifier. The "Mode" toggle provides a selection of either 9+ Watts with 6V6s, or 15+ Watts with EL84s, offering and exceeding the best tones available in some of our favorite late 50's American 6V6 amplifiers, and our favorite EL84/EL34 English amplifiers."

- Two inputs, each gets its own 5879 tube
- One is biased bright and clean, the other is biased gainier and with more low mid emphasis (probably coupling cap values and cathode bypass resistor + general bias point differences)

If you look at the Bassman 6G6A schematic I attached, you can see an example how how two channels with different preamp tubes and mixed later in the circuit are commonly arranged - the difference here would be that it would be just one pair of hi/lo inputs that split off to the two different stages - basically jumpered internally.

Here's also a schem for the FTR37 which might give you a clue about how that rotary tone stack is put together - the 9/15 is worded like it's just selecting different bright cap values to shift how low the corner frequency extends down into the upper midrange. This FTR37 schematic selects different coupling caps after the first stage that target the low end/low mids, but the general idea would be the same, just located around where the bright cap is implemented.

As far as the 6V6 vs. EL84 switching - they're both cathode biased sections so I don't see anything particularly tricky happening there - just a clever switch to select which output tube section is in circuit that manages to avoid any major noise or disturbance.

Thanks @jbrrrr, I appreciate the response. My interest lies mainly in figuring out how the two 5879 stages are wired. As you noted, the click tone control is available from other schematics, and the variable output tube section is not of much interest to me currently. Just looking for some pics or info on the 5879's.