** 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
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