Board Wiring for ECC99
The printed circuit boards are designed to fit into a standard star ground scheme. The two Amplifier Boards and one Power Supply Board should be wired like this (click to enlarge):
Board Wiring for 6N6Pi
6N6Pi has a different heater arrangement from the ECC99. The 6N6Pi uses only pins 4 & 5. Wire as shown (click to enlarge):
The Bijou Amp boards have split ground traces, one trace for the input and phase splitter stages and the other trace for the ouput stage. This keeps the high current ground signal from the output stage out of the input ground currents. These two ground traces are wired separately to the star ground, as you can see in the wiring diagrams above.
Do not wire across J1 unless you are having hum or noise problems that cannot be solved by any other changes. See the Troubleshooting section for more information.
Doing the Actual Wiring
Because the heaters use AC, the heater wiring has been kept off-board to eliminate hum that might be caused by high heater currents running through board traces.
The star grounding arrangement shown here should minimize or eliminate hum and buzz.
Screw type board-mounted connectors have been used to make board-to-board wiring as simple and flexible as possible. However, it is not necessary to use the connectors. They can be left off the boards and the wires soldered directly to the through holes.
The Bijou boards are designed to be wired together without the need for additional terminal blocks. You can use additional blocks if you prefer the wiring pattern better, but you don't have to. Here's how to wire without extra blocks.
Follow this procedure for heater wiring
- Make two twisted pairs of 20awg wire long enough to go from the PS board to each individual amp board.
- Connect these two pairs to the PS heater terminals, in parallel. Tighten down the connector screws.
- Insert the other ends of the pairs into the ECC99 heater terminal block, one pair to each amplifier board.
- Make two more twisted pairs that can reach from the ECC99 terminal block to the 6922 heater block. Be sure that these pairs are long enough to run around the outside of the board, away from the edges and close to the chassis. Do not run the heater wires under the board.
- Attach each pair to the ECC99 block together with the pair from the PS. Tighen down the terminal screws.
- Insert the short pairs into the 6922 heater block and tighten down the block screws.
The PS heater connections are automatically biased to 40VDC to reduce the HK voltage for the ECC99s. Nothing else needs to be done for a standard heater configuraion
- Make two 22awg wires (with at least 600V insulation) that can reach from the 250V terminal on the PS to each amp board.
- Insert the two ends of these into the 250V PS terminal block and tighen down the screw.
- Run each wire separately to the 250V terminal on each board. Tighten down the screws.
The star ground wiring can be done using a bolt that is first tightened down to the chassis with a lock washer and nut. You'll need solder lugs that will fit over the bolt.
- Make each ground wire that will reach from the star ground terminals on the PS and Amp boards to the star bolt.
- Solder a lug to one end of each of these wires.
- Insert each wire into its respective star ground terminal on the boards.
- Drop the lugs one at a time onto the bolt.
- Tighten the lugs onto the bolt with another lock washer and nut.
You can use other techniques to star ground, including auxillary terminal blocks, but the lug method is about the easiest.
Input, Output, and NFB Wiring
Make sure that you use insulated input and output jacks.
Input and NFB connections should be straighforward. Follow the wiring diagrams for running the wires from the jacks to the volume pot and from both pots to the Amp boards.
Run a wire from each output terminal to the headphone jack. Run the headphone jack ground to the star ground.
Make sure that left and right channels are consistent for the input and output connections.
Negative Feedback Pot Wiring
There are two possible ways to wire the NFB pot depending on what you want to show during the rotation. The fully counterclockwise position can represent either the Minimum NFB or it can show the Lowest Headphone Impedance. The clockwise rotation will then show the Maximum NFB or the Maximum Headphone Impedance respectively. This diagram illustrates how to wire the pot for either of these configurations.
Pay close attention to the way the wiper is wired for each configuration and remember that there are only TWO NFB connections on the Bijou amp board.