>Rich Measures wrote in response to Tom Rauch:
>>>The important point I was making is the grids belong grounded in a
>>>grounded grid PA. Any time any grid is RF coupled directly or
>>>through a divider to the input or output circuit, stability is decreased.
>>
>>Apparently, Collins didn't think so.
>
>Well, put it this way... any time you apply feedback to an amplifier, it
>partially connects the output to the input, making each port more
>sensitive to the termination at the other. Feedback that is negative in
>the operating frequency range will almost certainly turn positive in
>some different frequency range.
Verily. I haven't a clue as to which frequency they were aiming at.
>>I have never heard of an
>>instability problem with the Collins 30S-1 amplifier, and the grid is RF
>>coupled directly to the cathode.
>
>Ahem: not in the circuit I'm looking at. The control grid is connected
>to a capacitive divider between anode and ground, ...
I stand corrected, Mr. White. [see Figure 18 at:
http://www.vcnet.com/measures>]
>... but not connected to
>the cathode by any external components. Drive is applied between cathode
>and ground through the normal switched pi-networks.
The question seems to be: What is the RF potential difference between
the cathode and the grid under max. signal conditions.
>Here's another one to chew on. The 30S-1 has a parallel R/L network
>connected to the anode, but it does NOT go to the tank circuit!
Chewy indeed. However, the tank RF potential and the anode RF potential
should be quite close.
>The tank
>circuit connects directly to the anode and the R/L goes to the top of
>the capacitive feedback divider. ...
What is the value of L116?? L101, which also connects to the anode, is
another curiousity. A Collins engineer (W6HW) said there was inductor
connected to the anode that was made out of a Ni-Cr alloy. However, I
was not able to confirm this from the Collins drawings. An owner of
30S-1 could find the answer with a strong magnet since such alloys are
slightly magnetic.
>I wonder what happens without the R/L?
Knowing Collins, I'm guessing that it is there for a reason.
>
>73 from Ian G3SEK
Rich---
R. L. Measures, 805-386-3734, AG6K
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