4x HT50 or 55 do well on 2m with 4CX1000/3CX1500A7 amps.
GI7b and similar tubes drift when cooling is insufficient.
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73
Peter
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-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] Gi46b on 2m - Thermal drift problem
Datum: 2024-01-04T17:29:29+0100
Von: "Jim VE7RF" <jim.thom@...>
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For the OP, does that plate block cap even look like a cap at? 144 mhz ??? ?Will it handle the calculated rf current flowing through it at 144 mhz ??
John Lyles,? K5PRO helped myself and Scott out on that 10 kw 6m amp.? ?John used his test gear during a 3 way phone conversation, and was testing various HEC / centralab caps, like the 200 pf? and also? 500 pf variety, in both HT-50/58 size, and also HT-57 sizes.? On some of them, the SRF freq (self res freq)? was as low as just 42-45 mhz.? If 3 x caps were in parallel, SRF rose to 62 mhz.? On the HT-57 caps, in 200 pf size, SRF was 60 mhz...and? even higher, when paralleled.?
Above the SRF freq, the cap looks inductive.? ?It's straightforward? test process to find the SRF freq for a given combo of single, or multiple caps in parallel.?
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