1st test of revisited Pleiades V6 1H4 with male or female voice

At your risk:
Take all safety precautions.
A suitable fuse fuse should be connected in series with any battery for fire hazard protection.


Signal path:


male or female voice - Shure SM59 at 16in to 30in - Pleiades V6 1H4 with Altec input, output transformers - Sony TC-D5 Pro or Realistic Disco Mixer - Sennhesier HD5800


Very natural, smooth sound with nice articulation, clear sound


SM59 going direct to Sony sounded with a bit more treble but more bass, treble heavy sound.


Pleiades V6 1H4 feeding Realistic disco mixer had much more treble detail than other combinations.
This is possibly because of much less loading on the Pleiades pre preamp by the (10KΩ?) Realaistic Disco Mixer input impedance.


Female vocal sounded very nice at 30in.


At less distance there was proximity bass boost effect.


Even at such high distance with soft singing and the excellent SM59 great sounding but low output mic there was a good signal to noise ratio due to the very low noise figure of the Pleiades V6 front end.


There was buzz when connecting to the unbalanced Realistic but it disappeared when touching the transformers. The bug is that the pins 3 of XLR (needed really for both balanced or unbalanced connection) are not connected yet. Effectively it means that shields of transformers are not directly connected to the unbalanced ground.


It may take some thought as by looking at the Altec transformers schematics and the Pleiades V6 schematic, the metal body of each transformer would be at a different potential which may cause a problem if the 2 are accidentally short circuited. The battery will become short circuited.


It is being considered therefore to rearrange the schematic with both transformers on the Vb circuit.


The resultant schematic looks interesting with electron tube at the bottom, capacitor to the left of grid input transformer secondary above it, Pleiades bias resistor from anode to grid, output transformer primary above anode, Vb eg 12V connected at secondary of input transformer and primary of output transformer, heater 1.5V battery connected to direct filament cathode.


A fuse must be connected in series with any battery for fire hazard protection.