Passive amp set up for Radford ST25 amplifier

[dpgals]

Dear all

I have just inherited an home built amplifier from a friend that was built using the Radford ST25 circuit in 1986. The mains and output transformers were direct from the Radford factory, wound by their super expert lady winder who they got out of retirement in 1986 when they started building them again! I have replaced a number of capacitors that had passed their sell by date and generated a lot of smoke when I switched it on, and the amp is now back up and running after nearly 20 years of being sat in someone's bedroom cupboard. I have tried it connected directly with my level adjustable CD player and it sound pretty good through my Quad ELS 57 speakers. However, when I tried it in my system running a passive amp with a couple of Glass House mono 47 step attenuators, the sound is no where near as good, very thin and lacking in energy. I use the passive with my Leak Stereo 20 power amp with no problems at all and it sounds great with this amp. I also have to turn the attenuators well past the 80% level to get an decent volume. Could the degradation of signal be due to mismatch of impedance. I have now measured the load resistors that are connected to the the attenuators and they read 50k. From the information on the amp circuit diagram, there is a 100k resistor from the input to earth. Could this be causing a mis-match on impedence between the passive and power amp. If so, suggestions about how to address the issue would be more that welcome since I would love to try the amp out properly set up in my system.

Kind regards

David