On Sun, 3 Aug 1997 20:12:10 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>
>It seems to me the capacitor could easily be well within its rating.
>The limiting factor would be tuning drift, and it would appear LONG
>before the rating was exceeded.
>
>>it appears that the amplifier's designer made an engineering
>>error.
>
>It's tough to tell since your long drawn-out condemnations
>are based on incorrect, misinterpreted, or missing data.
IMO the above statement should be applied to its author as well. At least
on this list we have an administrator that permits the discussions to
play out without heavy handed censorship.
>
>Rich, it seems really silly to spend so much time publishing
>incorrect information just to find fault with one single little
>$5 doorknob in a $3000 amplifier.
>
>Have there been a rash of field failures in this component?
Rash? No but a rather steady history of failures over the years. The two
100pf HT50 type doorknobs that are switched in on 80M are more failure
prone when compared to the additional 500pf that is used on 160M. This
may be due to the simple fact that a stock 77 (of any flavor) can output
considerably more power on 80.
Since I am not in the position to analyze exactly why the failure
occurred I will not add to the considerable verbiage. My contribution is
strictly as a supplier of replacement capacitors over the past 11 years.
Many customers have opted for the larger 857 (HT57) series while others
have stuck with the original type.
There also appears to be a misreading of capacitor readings for the
500pf. In the HEC catalog they list the HT-58 and HH-58. The 500pf HT-58
with a N-4700 TC is rated at 3.2A at 1 MHz. The 500pf HH-58 with a X5T
TC is rated at only 1.4A at 1 MHz.
Since I do not have a 77 here to look at I could only hope that they were
smart enough to select the HH-58 style from whatever source they used.
If this is duplicate info, excuse the waste. I have been away for a few
days and trying to play catch-up with my mail.
replaced the
As I
>said, my friend's two tube 8877 ETO ran just fine on 160, and I used
>it hard for several weeks. He's used it for YEARS and he mainly works
>160 and 75. I asked him if he had any problems and he said no, none
>at all (except for a metal support arcing to a resistor, that I
>repaired).
>
>73, Tom W8JI
>
>(My opinions are my own. I am an independent consultant for several
>manufacturers and government agencies. I have no vested interest or
>control beyond supplying data and making suggestions. I do receive
>royalties tied to the sales or use of certain paten
>ted RF
>medical devices.)
>
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>
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