PCL84 record player amplifier

PCL84 is originally made for television. Triode section was designed for keyed AGC, sync. pulse  separation, sync. pulse amplifier and noise cancellation. Pentode was designed for video output stage. PCL84 has parallel model ECL84, that has 6.3 heating voltage. Other characteristics are identical.


Remembering the age of PCL84, the tube is quite common. Reason for this might be, that there is no reasonable applications after televisions used tubes. PCL84 was used in small scale for audio amplifiers spesifically in australia. Philips published also data for these applications. At the time a good quality Spice model is available for ECL84. This model can be used for PCL84 directly. 


Characteristics made PCL84 suitable for television make PCL84 also suitable for audio use.  The transfer characteristic is high and that means low driving voltage on gate. Minimun plate-cathode voltage is low and this means high output power compared to maksimum plate dissipation and current. Amplification factor of the triode  is about 65 making it as a good choice to drive the pentode section.  The characteristics of the triode section are near ECC81. Relatively high heating power may be  the worst disadvantage for audio use. PCL84 is designed for 300 ma filament current. This migt be also a problem. Fortunately heating voltage is 15 v and it can be formed from 6.3 v using voltage doubler circuit.  



Appearance of amplifiers is a common problem for every of amplifiers regardless of tube used.  Some details of appearances can however be  attached tightly tubes used. PCL84 is one of this kind of tube, that dominates the appearance of the amplifier. The small size of PCL84 is the feature, that has strong influence for the amplifier. The small size of the tube allows the use of delicate constructions. It is possible to install tube totally inside the cabinet without extra height. 

Reasons, why PCL84s are rarely used in audio amplifiers, we can only guess.  Besides heating voltage the most significant reason could be low plate dissipation. The output power of ultralinear push-pull connection is about 5 W.  One reason could also be lack of tested circuit diagrams. PCL84 amplifiers should have other advantages than output power, if the construction of these amplifiers is reasonable. Fortunately PCL84 suits extremely well to audio purpose. The latest simulations have shown very good characteristics for PCL84 audio amplifiers.  Using four tubes thd is extremely low for both ultralinear and parallel push pull connection. Again with four PCL84 output power can be about 20 W in push pull connection and a couple of watts lower in parallel push pull amplifier. These are at the time only simulation results, that can however be converted to measurement results when Metal boogie amplifiers are gradually completed.


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