Part 1 of this series about the development and building of a field coil speaker system showed the first trial for a bass cabinet and the selection of drivers and horns. The Kilimanjaro Series woofers will initially be fed from a lab supply. Later this will be replaced by my own PSU. Today I will show the building of the field coil supply for the A2000 horn drivers which are equipped with high voltage field coils.
The switch matrix for fine adjustment:
The backside with switches and connectors. Two different connectors are wired in parallel for the field coil voltage. 2 sets of banana jacks and an amphenol screw type terminal which provides connection for both drivers:
The two handles are convenient for moving the PSU around since it is quite heavy.
The power supply in operation:
Voltage is set for 90V per driver, 180V total. 300mA current.
The power supply operates nicely and stable. Voltage adjustment can be done while the supply is on. No need to power down for switching between the taps. This is easier on the TV dampers since one of the main factors determining liefetime is cycling of the heaters. Not that it would be a big issue since these rectifiers are very cheap.
The 6CG3 seems to be the perfect choice for such a supply. I'm using it since quite a while in the power supply of 211 monoblocks and it works flawless there in a voltage doubler circuit which is quite demanding. I expect them to last many years in the field coil PSU. No special precautions were necessary with regard to heater-cathode voltage. The heaters are simply referenced to ground. Since the 6CG3 draws a bit of heater current (2.1A) two heater windings are used. Two tubes share one winding. The photo on the right shows a nice close up of a 6CG3 in operation. There are other TV dampers who could be used for this purpose as well. For example 6CJ3 or EY500. The latter is probably easier to be found with heaters for series string operation. That is the PY500. The american designations for the these tubes are 6EC4 and 42EC4.
Before listening can start, the speaker needs a crossover. This will be a active set up with a passive crossover placed between the line stage and the separate power amplifiers for horn drivers and woofers. The next part will show the initial version of this crossover. Stay tuned!