[Amps] Looking for Alpha 87A expertise
w6fdu at aol.com
Sun Mar 14 22:31:56 EDT 2021
>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:
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?
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.
>> On Mar 14, 2021, at 3:16 PM, Steve Thompson <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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