I'm assuming by the large value that C1 is the output or loading capacitor of a Pi tank but I'm curious as to why the fixed capacitor are in circuit all of the time regardless of the frequency band. That part doesn't computer with me. Maybe it doesn't cover all the HF bands?
Adding an extra capacitance to the output of a Pi circuit will lower the value of minimum impedance that the circuit will load to for a single frequency and coil setting. But since it is a fixed amount of capacitance then the highest load impedance that it will load into is lower than before. For instance if it was designed for 40 to 700 ohms load then it may now be 35 to 625 ohms. These numbers are not real, just representative and the scenario is for a single frequency. John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John King Sent: Friday, April 04, 2008 1:37 PM To: [email protected] Subject: [AMRadio] Parsllel capacitors for C1 Need a little technical consultation, if you can run this through your head for me. I have an AMP Supply LK 500ZA amplifier using two 3-500Z tubes. The tank circuit was designed and built very rinky dink and light weight. Otherwise, it is a fairly well built amp. I have had to rebuild the tank circuit and put a heavy duty band switch in it. The amp had a C1 in it comprised of a 250PF variable paralleled by two fixed 200PF caps that stayed in the circuit all the time. My question is since I don't have two two 200PF caps, would one 500PF @ 20,000KV doorknob do the job? With this change, I will have 750PF instead of 650PF at C1. Something in the back of my mind tells me that one can run into trouble when paralleling variable caps and fixed caps because it changes the minimum capacity available from the variable cap. What are your thoughts on this based upon your knowledge and experience? I can provide you with a schematic of the tank circuit directly as I have scanned that part of the tank circuit. ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
