[Amps] help sorting out ETO (ETD??) amplifiers ??

[Dan Sawyer]

All,

I recently purchased an older ETO (ETD?) amp with 2 MRF 136 transistors. 
The part descriptor is an AB-041. Does anyone know anything about this amp?

There are 5 transistors on the board. Two are the output drivers. Two 
more appear to drive the bias network. I have traced the plus 24 volt 
input directly to the second set. I can't figure out any purpose for the 
5th transistor.

I can figure out the purpose of about 70% of the components. That said 
the output appears to be balanced as opposed to unbalanced. Both leads 
of the output x'former are outputted. Can one be tied to ground?

There appear to be 2 ground planes on the board. One is defiantly 
related to the 48 volt supply. What is the purpose of the second ground 
plane? The 2 planes are heavily bypassed with caps. What is the basis of 
this design? Can to the 2 planes be tied together? What is the purpose 
of this second plane? It is on the outside of the board on one side.

Thanks,
Dan