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[AMPS] Caveat on Dentron Filaments + MLA-2500B Notes

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Subject: [AMPS] Caveat on Dentron Filaments + MLA-2500B Notes
From: (Tom Rauch)
Date: Sun, 30 Jul 2000 07:44:06 -0400
> >?  The MLA commits one of the worst layout errors known --too much
> >distance between the anodes and the Tune-C
> >
> >You have got to be kidding! The distance is 5 inches..

5 inches is a long distance, unless there is no other option.

> >The other day you mentioned Alpha 77SX's using non-RF rated padding
> >caps...I have had several SX's and repaired several. They all use RF
> >rated door knob caps. 
> ?  RF rated caps come in two flavors, for use in tanks (-750ppm) , and for
> bypass use.  Bypass caps are not suitable for use in tuned circuits.  

Transmitting doorknobs are all RF rated. The temperature 
coefficient is a offshoot of the amount of capacitance and voltage 

At about 200 pF and 5 kV a single-layer ceramic capacitor is 
forced into the next higher range of N3300. The greater the 
capacitance, the higher the temp coef.

Below 200 pF, you can normally purchase N-750 and at very low 
values NPO types. None of this has anything to do with the 
capacitor being a "bypass type".

> > The trouble is that the 5 kw output is too much for the 160m
> >load padders and they get hot and drift. 
> ?  ...  tank circulating current with two 8877s is about 20A.  The 160m
> padder cap that is used is rated at 1.4a max @1MHz. 

The padder cap gets a portion of the current, and the current rating 
increases with frequency. The rating is also only for a given 
temperature rise, and can be substantially increased if the 
capacitor is mounted to heat-disippating surfaces and if the 
capacitor drift is not a problem.

The ratings explanations in the Jennings/HEC catalog cover all of 

73, Tom W8JI

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