** Tnx, Frank. What OS are you using?
-- According to ITT-Jennings, their small 500pF and 1000pF doorknob
capacitors are for bypassing and coupling applications only because they
use a temp-unstable dielectric. For tuned-circuit padders, one needs to
use N-750 100pF or 200 pF, 7500v units, paralled if necessary for more
C. In commercial MF amplifiers, I have seen two square aluminum plates
with up to 16, N-750 doorknob caps in parallel.
-- In the Alpha 77, not only are the wrong type dielectric capacitors
used for tank padders, the tank circulating current they are subjected to
is above ITT-Jenning's current ratings.
cheers
>Replace each "strange" char with a "0". Then you get "500 pF".
>But I'm sure you knew already ;-)
>
>Another one of that character encoding sh.. !
>
>73, Frank
>
>
>On Thu, 2004-01-08 at 13:33, R.Measures wrote:
>> ** 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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>> >Amps@contesting.com
>> >http://lists.contesting.com/mailman/listinfo/amps
>> >
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>
>
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