[HomeBrew] Neutralization circuit question

[kwylow zinjanthropus]

All:

I have a question with regards to the 1962 ARRL Handbook "90 watt amplifier" neutralization circuit. I modified the input circuit so that I'm not using a link input per the original circuit. Instead, I'm running a conventional plate blocking cap to LC circuit (which comprises of a 140 pf variable and a bandswitched coil taken from the osc circuit of a Viking 1for my 6AG7 osc circuit). The output is fed to a 15 ohm/1 watt carbon resistor going into the 6146 grid (which I assume has something to do with lessening the amount of grid drive? I dunno. Please let me know why the 15 ohm grid resistor).

Anyway, the ARRL circuit calls for the bottom of the 6AG7 tank circuit to be connected in series to a 680 pf cap which is in turn, hooked to ground. In between the tank circuit and the 680 pf cap is a connection to a 10 pf variable cap to the plate of the 6146. This is the neutralization adjustment cap. From what I see, the variable cap and the 680 pf cap forms a signal voltage divider for neutralization purposes. Now why must the 680 pf cap must be connected between the LC tank circuit and ground? How will this affect the drive coming from the 6AG7 osc? From what I see (using the formula for cap reactance 1/(2piFC), I expect to see an impedence of several meg ohms as a result of the 680 pf cap. Normally, the 6AG7 tank circuit's bottom is hooked to ground. Am I missing anything here or is this o.k? 

Finally, I was advised to expect at least a 2KV "operating/breakdown voltage" when plate modulating the 6146. I'm going to ensure that the 10 pf neut cap will have that rating. How about the 680 pf cap? Must this also be of a significant voltage rating or will a convention mica cap do ok? I suspect that the neut cap should be effective enough to block any plate developed voltages from entering the voltage divider circuit.

Let me know what is up with this and thanks.

Cal, N6KYR



---------------------------------
Do You Yahoo!?
Yahoo! Health - Feel better, live better


---------------------------------
Do You Yahoo!?
Yahoo! Health - Feel better, live better

--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---