How do you remove the amp out of the H&K Tubemeister 18 Combo?

Hello,

I've had this amp for over five years and the tubes are beginning to degrade and getting noisy.  (It has the 10" speaker.)  

I could not find any online videos on how to remove the amp from the Combo cabinet to change out the tubes. I found an online article that indicated I need to remove the two top screws from the rear corner brackets and that they were the only screws/bolts needed to be removed. I did that but the amp does not budge.  Is that the only screws/bolts that need to come out?

Does anyone have any recommendations on how this comes out of the cabinet? Does it pull straight out the back?  Does it drop a bit and then pull out?  Where do you pull or push or pry on the amp to loosen it for removal?  How much force do I need to apply to get this out?

Thanks!

**UPDATE**  I resolved my problem and updating so others can gain access for tube replacements on the TB 18 Combo.

Removed the six rear panel screws along with the two bolts from the top rear corner brackets.  With sufficient steady force, I lifted up on the edges of the rear panel until the entire assembly began to move.  Continued that upward lift force until the entire assembly became free.  I disconnected the speaker wires from the speaker terminals and removed the amp from the cabinet. ]