Linear Amplifier with GU50 450W (ГУ-50) 27-28 MHz

This amplifier is based on schematic of famous Zetagi BV131, but instead EL519 6KG6 which is very expensive today I’ve used Russian military tube GU 50, which is actually copy of famous Telefunken Wehrmacht LS50, and the main reason I used it is because I found few complete Russian military HF amplifier UM-3, at the junk yard :), with EL84 / 6P14P / 6P15P and GU50. It’s rated like 50W amplifier, and it’s classic cathode grounded circut. When I finished this little beast in GG connection I was really surprised with differencies of sensitivity of tubes. I have big stock of more than 500 GU50 tubes, and I’ve tested more than twenty in this linear amplifier, and usually they delivered a bit more than 200 Watts, but few of them were very close to half of KW!!! That’s problem with USSR tubes, they are same type, even same batch and date of production, but so, so different in gain!!!

Linear Amplifier with GU50 450W (ГУ-50) 27-28 MHzLinear Amplifier with GU50 450W (ГУ-50) 27-28 MHz

Complete linear and amplifier is in this small cube!

Of course, that I planed completely new front panel, but I never did it.

Back of amplifier, tube socket and integrated tube cooler, 220V input and RF output.

A look under the hub, original instrument and relay were used, also switches, RFC. This torus transformer is just for heating of GU50 and relays.

Under the chassis, the secret of small size is in high voltage power supply, multiplier directly from 220V!

This is few hours modification I’ve done almost 25 years ago, when Zettagi was unobtainable and expensive in ex Yugoslavia.


This Post Has 4 Comments

  1. moha hara

    very nice ,i am a tube&tube radio collector in iran

  2. bravo2zero

    I some how doubt that gu-50 puts out 450W 45watt more likely. if you want 450 watts then try the gu-81.

    1. James

      I’ll second that

  3. Јеврем

    Russian tube data are correct,interpretation of data is usually incorrect,or misunderstood. Western “specialist”,with out too much real knowledge,trying to convert Russian terms and data under western terminology and it cause the big problems.Russian book usually very clearly says what is data presented in the book!Since Russian data requires more mathematics,then data has been “translated”,but,in turn,translators suffer from lack of language knowledge and then-same of translated data I have seen are baloni story.Mark > means that something is bigger than specified number,and it is not problem if you know how to deal with it!For example,trans-conductance is something you shall never find in Russian data book.This term is invented on west without too much technical reasons,as term “music power” ,it is nonsense…Also,GU50 is very popular among Russian radio amateurs,and there are thousands of them with utput power around 400W,BUT,their amps use FOUR GU50,not single one…..

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