On May 31, 2004, at 6:06 PM, carl seyersdahl wrote:
I get the feeling that some may have misunderstood my question about
the
resistors.
I was referring specifically to the RF negative feedback resistors
as used
in the ckts. per Mr. measures's pages.
IE; , two caps of .01 mf. each from the pi-net input ckt , to one
each 10
ohm resistor on each side of the "filament ckt" of a G-G amp. (572b's)
VS
using two ten ohm resistors in series from One .02 cap off the input
ckt to
the "fil." or cathode (as the case may be) ...!!!
Rich::: maybe you are the one to answer this one.!!!
Hello, Carl -- On 160m, driving both filament leads results in
applying equal drive to both ends of the cathode/filament. However,
since 0.02uF represents only c. 5Ωs of XC, this is no big deal. cheerz
Please ????
carl / kz5ca
----- Original Message -----
From: <peter.chadwick@Zarlink.Com>
To: "carl seyersdahl" <carlseye@tampabay.rr.com>
Cc: <Amps@contesting.com>; <amps-bounces@contesting.com>
Sent: Monday, May 31, 2004 6:44 AM
Subject: Re: [Amps] feeding the input
Carl was asking about feedback resistors in cathode/filament circuits.
The answer it that it seems to vary. The Mullard data sheet for the
QY3-125
(which is basically a 6151/ 4-125, as opposed to 4D21/4-125 - the
difference is that the 6151 doesn't have the metal base shell)) says
that
RF return connections should go to pin 1. The QY4-400 ( a 4-400) has
no
restrictions, although it's basically the same sort of device. The
QY4-250/6152 also suggests returns to pin 1 on early data sheets.
The Philips version of the QY4-250 (QB3.5/750) says nothing about
filament
returns but says that both screen grid pins should be used to
equalise the
currents.
With both QY4-250 and 4-250A's, I have resistors in both sides. They
have
series caps (old fashioned molded mica) of 0.01mFd so that I don't
heat
the
resistors with filament current.
I guess this probably doesn't help too much - it seems it's 'pays your
money and takes your choice' matter.
73
Peter G3RZP
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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