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Author Topic: 70cm amplifier by W1QWJ  (Read 642 times)
9A5BDP
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Posts: 224




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« on: November 18, 2017, 02:04:15 PM »

Hi there...

During this long rainy days of continental autumn reading of technical articles is my hobby. Currently I read "Requirements and recommendations for 70-cm EME" from June 1985/Ham Radio. On one place this text have note regarding 4CX250 linear amplifier design by W1QWJ. After some searching on net, only some partial drawings appear on my screen. Tell me folks, are any of you have in your library, maybe, additional constructional drawings and notes for that amplifier? Any help will be grateful..Apparently this linear amplifier design was published in QST in year 1976.

With best regards from Europe

73!

Dubravko
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AA2UK
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Posts: 316




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« Reply #1 on: November 18, 2017, 04:35:54 PM »

Are you talking about running a pair of 4CX250B's? If so look for the K2RIW 432 1kw amplifier.
http://www.g4ohv.com/k2riw.html
Also W2GN.
I have a K2RIW 432 I no longer use it was a great amp before SSPA's were available.
Bill, AA2UK
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W1VT
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Posts: 2493




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« Reply #2 on: November 18, 2017, 05:20:06 PM »

http://qrznow.com/the-vhfuhf-dx-book-2017-replica-edition-is-now-available-for-free-download/

This book has detailed information on building and operating the K2RIW amplifier.
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KM1H
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Posts: 2502




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« Reply #3 on: November 18, 2017, 06:08:35 PM »

A search of the QST data base from 1970-95 comes up blank but I believe the 1976 ARRL Handbook has that amp on page 232.

https://ia800401.us.archive.org/27/items/RadioAmateurHandbook1976/radio-amateur-handbook-1976.pdf

The photos are poor and I think I have that year along with a good modern laser copier.

I originally built it for CW/SSB and later moved it to FM simplex for contests. The cavity was standard copper pipe. I knew Dick, W1QWJ, well and sold him many small parts for his projects.

Carl
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K1ZJH
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Posts: 3310




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« Reply #4 on: November 18, 2017, 09:15:15 PM »

That design was around for awhile, since I built the PA cavity as a metal shop class project in the mid 1960s! But, it was a W1QWJ amp; as I recall the 'RIW designs used stripline and not cavity plate tanks.

Pete
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9A5BDP
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Posts: 224




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« Reply #5 on: November 19, 2017, 03:58:00 AM »

All books are downloaded and ready for reading. Thanks guys for links. For amplifier of my interest please open following document:

http://www.vra.be/teksten/Dossiers/VHF-UHF%20versterkers%20deel%207.pdf

And go on page 42, some pictures and explanation exists. This design is not cavity one, nor parallel like RIW design, amplifier is true push-pull. This amplifier have resonant circuit manufactured of copper thick wire (maybe tube).

Dubravko

73!
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KM1H
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Posts: 2502




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« Reply #6 on: November 19, 2017, 02:45:40 PM »

You can use the Svetlana GS-36B/4CX400A in a one tube amp and get the same power and better IMD than a pair of late 1940's designed 4X150A. The 1962 4CX250B is just an upgraded version with ceramic instead of glass insulation and better cooling.
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9A5BDP
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« Reply #7 on: November 21, 2017, 11:25:17 AM »

Svetlana (all soviet era) tubes are great for building linear amplifiers but I have on my private stock several pieces of used and even five new non-used 4CX tubes. For that reason I want to build 4CX based amplifier. Thinking to go on uncharted path of remake (after recalculation of all component values) W1QWJ amplifier based on few details published in stated dutch article. Any help with additional data or photos will be great. Thank you guys in advance...

73!

Dubravko

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