How to increase size of Transcript

When writing to  Transcript using Transcript show:, after certain amount is 
put on the Transcript, the screen gets cleaned, keeping only about 10K of 
text.

Is there a way to increase the amount of text Transcript keeps before 
cleaning? 

Thanks Milan

PS: I tried to inspect the Transcript model (TranscriptStream) and modify the 
readLimit and writeLimit but it did not help.