[HomeBrew] TO-3 transistor insulator question

[Philip, KO6BB]

Hi All,

I have a question here that I really 'should' know the answer to myself.

I'm repairing an Astron RM-20 power supply for a friend.  I have repaired 
this 'critter' once before, installing new pass transistors (2N3771) in it. 
It again needs new pass transistors.  The ORIGINALS used the old mica 
insulator and white thermal grease.  Before, when I replaced the pass 
transistors I used the newer style gray silicon rubber insulators WITHOUT 
grease.  They are SUPPOSED to be superior to the old mica insulators.

Question.  Are the newer silicone rubber insulators 'really' better, or 
would I be better off going back to the mica (I have both on hand)?

The RM-20 is being used to power a Kenwood TS-430 100 watt HF rig, and I 
suspect that the unit is approaching the limits of it's capabilities (15 Amp 
continuous, 20 Amp intermittent ICS).

Inquiring minds want to know 8^)

73 de Phil,  KO6BB
DX begins at the noise floor!

Ten Meter CW Beacon KO6BB/B, 7 Watts 24/7 on 28.248MCs.
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Merced, Central California,    37.3N  120.48W  CM97sh