Follow this procedure to set up your Bijou for the first time. The first step is to ensure that the power supply is working properly, then the heaters, and then the full amplifier.
The Power Supply
- Connect the power supply board to the transformer. Double check the wiring to make sure that the HV and Heater secondaries are attached to the correct terminals on the board.
- Connect the board to the star ground point.
- Connect the ground for the line (mains) to the star ground point.
- Be sure that you are powering the transformer through an appropriate power switch and fuse.
- Attach a 100k/1W resistor to the 250V and Gnd output terminals.
- Double check everything.
- Attach a DVM set to at least 300VDC across the 100k test resistor.
- Power up the PS module. The EZ80 should light up. If it does not, turn the power off immediately and recheck the transformer connections.
- If the EZ80 lights ok check the voltage shown on the DVM. Adjust the trimpot, P1, until the output reads 250V.
WARNING: This power supply uses potentially lethal HIGH VOLTAGES, more than 300V in certain places. Construction and testing of this PS should only be done by someone who is thoroughly familiar with safety precautions around high voltages.
WARNING: If you short the output of the regulator while it is under power, both mosfets will be destroyed and you will have to replace them.
If the power supply comes up successfully, power off and wait until the output voltage drops below 10VDC before proceeding to the next step.
The Amplifier Tube Heaters
Before applying B+ to the amp you should make sure that your heaters are wired correctly. It is easy to make an error, particularly when wiring for either ECC99 and 6N6Pi.
- Leave the 100k resistor and DVM connected to the PS.
- Connect the heaters as shown on the wiring diagram in the Wiring section.
- Power up the PS module again.
- All four tube heaters should light up. If they don't power off immediately, check the tubes for open heaters, and double check the wiring. Make sure that pins 4,5, and 9 are wired correctly.
- If all four tubes light, power down and wait until the B+ is below 10VDC.
This is the final step in bringing up the amplifier.
- Connect input and output jacks, the volume and feedback pots.
- Remove the 100k resistor from the output of the PS.
- Make all Star Ground connections as shown in the wiring diagram.
- Connect the B+ from the PS to the Amp boards.
- Connect the DVM from a B+ terminal to Gnd.
- Double check everything!!!
- Power up the amp. If you see any smoke, power down immediately.
- If the tubes light properly and there is no obvious problem, read the B+ on the meter. It should be close to 250V.
- Let the amp run for about an hour and then readjust the B+ to 250V.
- After about 50 hours of operation readjust the B+ again to 250V.
There isn't much that can go wrong with this amplifier, but just in case . . .
The Power Supply
If anything smokes or burns up in the PS the likely cause is an incorrect value for one of the components, a component inserted incorrectly, or a short.
- Check the orientation of Z1.
- Check the orientation for all of the electrolytic caps.
- Inspect the board again carefully for any shorts between traces. Insect the wiring for the same problem.
- If the EZ80 doesn't light and the heater wiring is correct, then replace the tube
If the output voltage reads less than 200VDC and/or if adjusting the trimpot has little or no effect, the most likely cause is that the mosfets have been blown. Unfortunately, you'll have to replace them.
After replacing the mosfets, recheck all part values and orientations. If these are all correct and if both mosfets are good, the PS will come up to its specified voltage.
Typical internal PS voltages a shown on this diagram:
The amplifier circuit is simple and tubes are relatively indestructible. If voltages are off in the amplifier it is most likely caused by an incorrect component value or one or more of the diodes, D1-D6, installed backwards. The internal voltages of the amplifier are shown in the diagram below. It is not uncommon in tube circuits for some of these voltages to vary by 10% or so.
Hum and Buzz
If the star grounding technique is followed accurately, there should be no audible hum or buzz. If there is:
- Turn the volume pot all the way down.
- Check all of your ground connections to the star and at the points of origin on the boards.
- Check that your power inlet ground is also connected to the chassis.
- If there is buzz when you touch the volume pot, connect its case to the star by soldering a wire to it.
- Make sure that the heater wiring is twisted from connection to connection, is well away from the boards and signal wiring, and lies close the metal chassis.
- Make sure that the transformer and the rectifier tube are sufficiently far away from the signal wiring and amp boards.
If you've tried everything and still have problems, you can try changing the ground traces on the amp boards. To do this, follow these steps:
- Solder a wire across J1.
- Remove the star ground connection from the ECC99/Output connector.
- Do not remove the star ground at the Input connector.
If strapping J1 does not improve or solve the problem, it is best to remove the J1 jumper and restore the star ground wire to the ECC99 terminal block.