Hi Corelli,
The 518ia is a stereo chassis 845 output tubed amp (25 watt per channel). The 508ia uses the 805 as the output tube (45 watt per channel) this is the amp used by Waltersilas on this thread.
There is also the 219ia which is 845 tubed and is a dual mono stereo chassis design. You can google the LM 508ia, there is much praise for this model.
Charles