[AMPS] 'Glassmike' for blocking cap

[Tom Rauch]

Hi Vic
> 
> A guy on ebay is advertising Glassmike .04mfd @ 5 kvdc capacitors.  Any
> opinions on how this would do as a plate blocking capacitor for an HF amp
> with 3kv on the plates?  It looks large enough to have a reasonable
> current rating.


I wouldn't use it.

First, that amount of capacitance is totally unnecessary. 
Reactance of the blocking cap only needs to be less than 
somewhere around 25% of the lowest expected anode impedance 
on the lowest operating frequency.

Second, when capacitors are such high capacitance at such high 
voltage they are almost always either physically very large,  or a 
wound foil construction.

Third, you haven't had fun until the primary component that 
prevents anode voltage from appearing on the output connector fails.

Putting an unknown quality and spec cap in such a critical spot 
would be foolish.  Brand new 7.5 kV ceramic doorknobs are under 
ten dollars.



 


 
> 
> 73,
> Vic, K2VCO
> Fresno CA
> 
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> 


73, Tom W8JI
w8ji@contesting.com

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