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				RF tetrode 
				Introduced in 1927 
				(PM12A: 1932, PM12M: 1933) 
					
						| 1 | 2 | 3 | 4 | tc | base |  
						| g2 | g1 | f | f | a | B4 |  
					
						|  | Vf | Af | Va | Vs | Vg | mAa | mAs | ra | gm |  
						| PM12 | 2 | 0.3 | 150 | 75 | 0 | 4.3 | 1 | 180,000 | 1.1 |  
						| PM12A | 2 | 0.18 | 125 | 75 | 0 | 2 | 0.4 | 330,000 | 1.5 |  
						| PM12M | 2 | 0.18 | 150 | 90 | 0 | 2.5 | 0.5 |  | 1.4 |    
					
						| Equivalent | 215SG, S21, S215, S215A, 
						SG215 |  |