On Wed, 13 Sep 2006 13:09:43 +0100, Highland Ham
wrote:

Roger (K8RI) wrote:
On Tue, 12 Sep 2006 23:16:20 GMT, "SNOWDEN"
wrote:

Anyone been successful in building an amplifier at 6 meters? I have a
couple and was thinking about trying it.

I've not seen a 4-400 amp on six,, but they are rated to 110 MHz and
the book shows just shy of the legal limit out at 75 MHz.

I don't know how difficult the'd be to neutralize.
Sounds like fun and I think they'd be a better tube for six than
3-400s or 3-500s.
=====================================
Up to the mid 1970s type 4-400 transmitting valves (tubes) were used in
the UK in Band 1 (approx 45-65 MHz )TV transmitters.
For a 7 kWatts area transmitter there were 7 chassis of 2 valves each.
So they should be excellent for the 50 MHz amateur band.

A very early design can be found in QST March 1967 ,pages 11 - 15.
Titled : Six-Meter Kilowatt with 4-400As or4-125As.

The design involves 2 valves (tubes) in push-pull config.

Although push pull RF Power Amps are nowadays no longer or not
frequently used , I feel it is still interesting reading and might give
some ideas for a homebrew amplifier.


Many years ago, there was an article in QST (I think) that used a pair
of 6C21 radar pulse modulators in Push pull with copper pipe for a
tank circuit. I don't remember what they used for a link but I think
it was just a u-shaped piece of smaller tubing.

That thing would put out today's legal limit with a sneeze. Even more
if you turned the driver on.

Unfortunately 6C21s are big (bout 16" tall), difficult to find, and
expensive. I used to pay $5 USD each.

If you can't find the article , I can send you a scanned copy of the 5
pages.

To email me remove the obvious chars from the above address.

Frank GM0CSZ / KN6WH
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com