[Amps] Looking for Alpha 87A expertise

[Jim]

How much slower?


Thanks
73
Jim W7RY

On 3/14/2021 9:31 PM, Benjamin Deovlet wrote:
> From my design experience, the 1N400X diode is much much slower than 
> PIN diodes.
> Ben, W6FDU
> In a message dated 3/14/2021 7:16:26 PM Pacific Standard Time, 
> jimw7ry at gmail.com writes:
>
>     Doug...
>
>     How fast is a PIN diode?  How fast is a 1N4007 in an Alpha 87? If you
>     have not measured their speed, how can you make that statement?
>
>
>     Thanks
>     73
>     Jim W7RY
>
>     On 3/14/2021 7:59 PM, Douglas L via Amps wrote:
>     > I have doubts about replacing those PIN diodes with 1N4007’s.
>     The 1N4007’s don’t switch quickly enough to substitute for a PIN.
>     >
>     > 73,
>     > Doug/WA1TUT
>     >
>     >
>     >> On Mar 14, 2021, at 3:16 PM, Steve Thompson <g8gsq72 at gmail.com
>     <mailto:g8gsq72 at gmail.com>> wrote:
>     >>
>     >>
>     >>> 2.  Is a drop from 900V open-circuit to 730V typical when
>     >>> disconnecting/reconnecting the "R" bias lead at the HV board? 
>     I'm wondering
>     >>> if I have another leaky PIN diode or cap to ground that is
>     loading it down.
>     >>> It doesn't take much to load the bias supply given that it
>     inherently has
>     >>> 880k of series resistance.
>     >> I don't know the 87A circuits, but assuming the 900V/880k
>     supply is loaded with a reverse biassed diode with 3.9M across it,
>     the current in the 3.9M will drop the voltage to a calculated 734V
>     - close enough to what you're seeing so I'd guess it's ok.
>     >>
>     >> I'd hazard a guess that the 3.9M resistor(s) are there to try
>     and avoid problems from static build up.
>     >>
>     >> Sorry, can't help with anything else.
>     >>
>     >> Steve G8GSQ
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