Excellent figuring Peter!
An additional choke and bypass cap is almost essential to prevent
deleterious 1.8 MHz RF blow-by into the HV power supply electrolytics.
Mind you the HV "glitch" resistor also provides some attenuation of RF
leakage when bypassed with a ceramic cap.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of peter chadwick
Sent: Wednesday, 26 March 2014 8:48 AM
To: Carl; Rich Hallman - N7TR; amp reflector
Subject: Re: [Amps] HV limit for rfc-3 choke?
Figure it this way:
Suppose you have 5kV DC and a plate swing of 8kV p-p or 2800 RMS. 225
microhenries is 2545 ohms at 1.8 MHz so the RF current in the choke is 1.1
amps, in addition to the DC. If Q = 100, R = 25 ohms and the power loss in
the choke becomes 30 watts. That 1.1 amps needs a low impedance ground
return, so that means something of the order of maybe 5nF to ground. Larger
values can get too inductive on the higher bands... Even then, 5nF is 17
ohms at 1.8 MHz, so there will be about 20 volts of RF at the base of the
choke. That means you need another choke and capacitor to keep RF away from
the HV electrolytics.
I recently published an article in the journal of the Vintage and Military
Amateur Radio Society on this: I can send a copy if anyone has any interest.
73
Peter G3RZP
========================================
Message Received: Mar 25 2014, 08:30 PM
From: "Carl" <km1h@jeremy.mv.com>
To: "Rich Hallman - N7TR" <rich@n7tr.com>, "amp reflector"
<amps@contesting.com>
Cc:
Subject: Re: [Amps] HV limit for rfc-3 choke?
I know people using them at 5KV from a 4-1000 to 3CX3000; they appear to
hold up but I wouldnt want to experiment on RTTY with the 3X3 or bigger..
Carl
KM1H
----- Original Message -----
From: "Rich Hallman - N7TR" <rich@n7tr.com>
To: "amp reflector" <amps@contesting.com>
Sent: Tuesday, March 25, 2014 2:06 PM
Subject: [Amps] HV limit for rfc-3 choke?
> Will the rfc-3 choke work at 5kv? I know they say 4kv, but wanted to
> know if others are using it at higher voltages?
>
> Thanks.... Rich N7TR
> _______________________________________________
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