Those oem 220M? caps are each 2200 pf.? ( 6600 pf in total for all 3 of em in parallel).??
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The problem with discs is..... current handling capability.? ?Upper HF will result in the highest RF current through a block cap.? And high duty cycle modes like? 10M FM,? ?data, rtty, FT-8? will stress em.
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I bought some Ceramite brand 4700 pf @ 10 kv disc caps from Henry radio.? Then bought some Ceramite? 4700 pf disc caps, but this time in 15 kv, also from Henry radio.? ?Typ the higher voltage rated? disc caps also handle more current.
A few months back, I bought 3 x dozen? chinese? .01 uf (10,000 pf? or 103M)? rated at 30 kv....bought off their ebay site.? ?They came in 10-20-30 kv.? These 30 kv versions are monsters.... at 1.3" diam x 7/16" thick.? ?My hi-pot tester only goes as high as 15 kv.... and they draw 0 leakage current, even after 10 mins.... good enough.? ?They are cheap..and the shipping is dirt cheap.? ?The 11m ops use just one of the .01uf @ 20 kv versions for a coupling cap into the cathode of a GG high mu triode amp.
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So far, so good....with my limiting experimenting.? These chinese discs handle a stupid amount of current.?
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The pair of discs in the Drake? L7 ( also used for plate blocking)? ?are failure prone.
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The actual correct component for plate blocking is a? 5 / 7.5 kv rated HT-50/58 sized doorknob.....and 2 are used in parallel...and work good on 160-10m.? ?These days, you can only get the HT-50/58 doorknob caps in 7.5 kv.? They will handle one helluva lot of current on upper HF....per the detailed specs in the HEC catalog.?
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I have never seen a plate blocker blow up from high swr / no ant, open ant, shorted ant etc..at least not when using HT-50/58 sized caps.??
