[Top] [All Lists]

[AMPS] RIW amps

To: <>
Subject: [AMPS] RIW amps
From: (km1h @
Date: Wed, 25 Mar 1998 17:26:00 EST
On Wed, 25 Mar 1998 15:35:20 +0000 Mike Willis <>

>OK. Many K2RIWs do not work while other seemingly identical ones do. 

Attention to detail is the key. That design is 100% reproducible ...IF
you follow it exactly. Any deviation requires a pretty good knowledge of
the "gotchas".

And none of Dick Knadles designs have a parasitic suppressor either
Mike...altho a series HV resistor is suggested..
Dick and I had a one on one BS session after the NE VHF conference last
August in Enfield, Ct.. My original call was K2QJM so we sorta grew up
into this stuff together. Anyway the session lasted till about 230AM with
Diet Coke being the strongest drink available.  Even a local dingbat was
speechless since my past history at that convention has been partying
until the wee hours.  The year CO2KK was there was a classic..I  "think "
I went to bed at 430 AM..  Age does slow even the best of us down!

>The K2 style cooling system has been used a lot with the 4CX250B. It 
>not provide an air blast to the base. Does this matter ? I have never 
>trouble with it in my W2GN.

Not at the 500-600W level and low duty cycle. If you were to rebuild with
Svetlana 4CX400A's and go for 1000W + output then the cooling system
should be redone. The base heating does not change since the filament is
the same  but the overall heating does and gradually makes the complete
assembly intolerably hot.
If used for only a few short bursts then the original may be adequate.

BTW, for 70cm I am now running a AM-4155 conversion that does a very
stable 400W out with 10W of drive. Dont know the UK availability of this
60's era FAA amp but it is decent power for little money and an ability
to know which end of the soldering iron is hot. 

Still working on the "big"  70cm amp with a 2600W dissipation
tetrode...just picked up some 1 5/8" Andrew Heliax too....A local site
was trashing it! 

73  Carl  KM1H

>Why do 4CX250Bs show negative grid current above 2m before the onset 
>normal grid current?

That has been covered for over 40 years and is in the Eimac spec sheets;
QST amp construction articles, etc. I would not want to go into it here
and further annoy the appliance operators. But rest assured it is normal
and safe.

>FAQ on WWW:     
>Administrative requests:

You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at
Or call Juno at (800) 654-JUNO [654-5866]

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>