Help identify use of valve contraption

Hi all.

Me again
Got this old "contraption" from deep storage.

This thing seems to be an amp , very heavy, seems homemade or something.
It contains 3 pieces ... A pre , a power supply  and a power amp.
But what I cannot figure out is that between the pre amp and the poer amp there is only 1 RCA type connection , however there is left and right on pre amp for the input source(aux) and a left and right for speaker out.
The pre amp also contains a switch called "selector" with 5 selections , but there is only one input source  :walled:

The pre amp then also got knobs for treble and bass min and max , but then also rise and fall for each ,,, oh and it does have a volume knob .

Anyway's here are some pics (sorry cellphone quality and I did not dust the contraption off).
I opened the pre , but not the power supply or the power amp.
Enjoy  and please comment ,,, should I throw this away or try it ?


Pre:
http://instagr.am/p/SED5BMzbY3/
http://instagr.am/p/SED_WhTbY_/
http://instagr.am/p/SEEKuhTbZI/
http://instagr.am/p/SEEPIwTbZO/

Pre aux input and 6 pin din type from power supply :
http://instagr.am/p/SEG39DTbbi/

Pre to power notice single RCA , where did the other channel disappear to ?  :
http://instagr.am/p/SEG5EYTbbk/

Pre top view :
http://instagr.am/p/SEDyl0zbYv/

Power amp :
http://instagr.am/p/SEDqynTbYn/
http://instagr.am/p/SEC7uGzbYP/
http://instagr.am/p/SEC34SzbYK/

Power amp , notice single RCA from pre , but mow the other channel is back with the speaker out  :Whoohoo:
And then again a 6 din type coming from power supply :
http://instagr.am/p/SEC0AATbYH/

Power supply :
There is a huge valve that fits in the bigger circle next to the big transformer , I removed it and forgot to plug it back for the photo shoot .
http://instagr.am/p/SECuEXTbX9/
http://instagr.am/p/SECpvxTbX5/
http://instagr.am/p/SECGKyTbXX/

Shoo

Tx for anyone that can comment ...lol