The answer is:
to provide -2db negative feedback. This was done to match the output power
of the TR-3 and TR-4.
Also of note; it was the first 3-400/500 amp to have tuned input circuits,
The output circuit was designed to match a 2 : 1 SWR at all impedance's and
phase angles.
He also designed the MN-2000 which will match a 5 : 1 SWR at all
impedance's/phase angles.
At one time they were getting L-4s in for service which had the pi wound
grid chokes where the windings were " slammed together" .. This was from
plasma arcs inside the tube going thru the grid. He called EIMAC about this
and they said when the 3-500z are being vacuumed sealed, they put high
voltage on all the terminals to burn off the metal whiskers which form
during the process. Eimac said " guess we will have to let them burn off
longer " . After that the problem went away.
The cost of a 3-500 was 24.50 then.
Any other questions?
73 Jack N8DX
On Thu, Jul 30, 2009 at 10:00 PM, Thomas Carlsson <thomascarl@gmail.com>wrote:
> Interesting addition: LK-500 and its brothers have Grids direct to Ground,
> no components. Cathode resistor only 0.15ohm/3W.
> SB220 and L4(B) both 1ohm in cathode and they have the same grid
> components, on schematics I have the RFC and C's are copies of each other. 73,
> Thomas, PY2ZXU/SM0CXU
>
>
> On Thu, Jul 30, 2009 at 8:25 PM, Jack Shirley <jcshirle@gmail.com> wrote:
>
>> I looked at the various 3-400 and 3-500 circuits in the Eimac Amateur
>> Service Newsletters and did not find this mentioned anywhere.
>>
>> If the SB-220 and L4 use the same grid circuit, I could ask the engineer
>> who
>> designed the Drake L-4 as I know him personally. Any interest?
>>
>> 73 Jack N8DX
>> On Thu, Jul 30, 2009 at 6:48 PM, Ward Silver <hwardsil@gmail.com> wrote:
>>
>> > > perhaps somebody with an SB-220 and a spectrum analyzer needs to do
>> > > an IMD profile using each grid circuit and SEE which one produces the
>> > > cleaner
>> > > output.
>> >
>> > What?! And ruin a perfectly good thread?
>> >
>> > 73, Ward N0AX
>> >
>> > _______________________________________________
>> > Amps mailing list
>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>> >
>> _______________________________________________
>> Amps mailing list
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>>
>
>
>
> --
> Thomas, PY2ZXU/SM0CXU
> Member of the PW2D Team
>
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