Hi Paul,
i am now owner of a pair BC1-Germany- Speakers, Report follows here later.
I think its a late version of the BC1 with Fuse on backside and Biwiring terminals.
The Crossover Components have been changed by Spendor as follows:
View attachment 1461651
i will describe changes from top ( Coles Supertweeter )
1. Capacitors changed from input (left) side 1uF to 0,68 next 1uF to 0,47
2. Resistor 33 Ohms don`t exist.
Celestion HF1300 Tweeter:
1. Tweeter is connected in Reverse Polarity !!! ( The black cable is soldered to the red dot on the Celestion )
2. Capacitors 0,47 and 0,33uF changed to only one C with 1,5uF
Midbass :
1. One resistor 220 Ohm/5Watt is added parallel to the 3,3uF MKT
All inductors and coils values haven´t changed.
All changes look for me like made in factory, because the soldering points look virgin.
The ports of my BC´s are 3" diameter and have a lenght of 16 cm, at the output they have a phase. No foam was insert.
So i tried several versions of foam insert - with the result of decreased bass every time.
Only thing i did, was to put in foamliners of 4 Millimeters thinkness but complete lenght into the ports. This is a damping for some midtone frequencys reflectet from the backside of the midbass.
In my Spendor Preludes this will work good, without them i hear unnatural deepnes of the " stage "
Good Luck
Juergen