[Amps] ALPHA 77 RF POWER CAPACITORS

[R.Measures]

**  How much C is:  5ÿÿpF?

>
>Gentlemen,
>
>Not too long ago in this reflector a discussion was had about certain RF 
>power capacitors being prone to failure in the ALPHA 77Sx amplifier, more 
>specifically thus:
>
>  :: "The 16ÿm doorknob padder should have a higher ampacity."
>       From what I see of the schematic, C4ÿ: 5ÿÿpF/5KV is type 85ÿs.
>
>  :: "The two 8ÿm doorknob padders are prone to failure."
>       They are listed as C41,42: 1ÿÿpF/5KV, type 858s.
>
>  :: "The Plate Blockers are too light."
>       They are listed as C2ÿ,21: 1,ÿÿÿpF/5KV, type 858s.
>
>  :: "The Plate Choke RF bypass capacitor is prone to failure."
>       It is listed as C35, 1,ÿÿÿpF/5KV, type 858s.
>
>  Observed: The additional bypass caps on the plate circuit are
>            2,ÿÿÿpF/6KV disk ceramics. Two of these parallel a
>            15uH, 1 amp RF choke, L9.
>- - - - - - - - - - - - - - - - - - - - - - - - - 
>Questions:
>    1. What are your recommendations for upgrading the reliability
>       of the capacitors above? Several issues arise: E and I ratings,
>       and the best type: HT50, HT58, HT57...?
>
>    2. If the amplifier is capable of 2.ÿ plate amperes on the 'Sx 
>       version with two 3CX15ÿÿA7 finals, then is not L9, at 1.ÿ amp
>       prone to failure from over heating?
>
>    3. The capacitors paralleling L9, the disk ceramics, are rated
>       at 6KV. However, should their value of capacitance increase?
>
>    4. The 16ÿm and 8ÿm padders seem kind of light in capacitance for 
>       the new output impedance of two 8877's. Should not their value
>       increase dramatically to affect the tank's Q?
>(Reference: HV:3,9ÿÿVDC)
>(Vac.Var. changing to 7~1,ÿÿÿpF/7.5KV)
>Thank you for your opinions.
>
>Hal Mandel
>KA1XO
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>