Right
The 46 driver stage has been interspersed (sic) between the 6A6s and the PX25s. The resulting sound quality is a bit good I have to say. Direct, dynamic and with good detail.
I thought that, with the introduction of the extra gain stage, hum levels would increase. However, this has not happened. Therefore, in terms of noise performance, given the fact that the valves are all AC heated, I'm pleased with the performance of the breadboard.
One fly in the ointment though, is that the voltage I'm able to get the driver to swing is compromised by the resistor loading. It's not so much of a problem with the PX25, as this valve (gain 9) is quite easy to drive for DHT, but with something like a 300B, it might struggle unless a high HT voltage was available.
I've settled on an 11K load as one that gives a nice low distortion drive to the outputs. But of course being a power valve, the 46 would be far better served by transformer coupling it to the outputs or at least choke loading followed by cap coupling.
Nevertheless, even with less than ideal resistor loading, the 46 makes a superb driver, able to swing enough voltage and current to get PX25s singing. Transformer or choke-cap coupled, this little gem would hardly break sweat driving 300Bs.
Here's a pic:
I've put both the drivers together on the left of the audio board rather than having one sticking out on the right.
Now a question. Can anyone recommend a good interstage transformer capable of dealing with a standing current of around 30mA?
The Hammond 157G 30H 40mA choke looks reasonable as an anode choke and is cheap at £9.00. The Hammond 1 : 1 interstages look OK at 44H and 30mA and at £26 each are again relatively cheap.
Other ideas anyone?
Steve
This of course means that I could be bringing a pair of 5' 4" Metronomes to Whitham in the Autumn. Melanie has passed a pair of mock ups as fit to grace the living room so watch this space. 
