Simplified Amplification

UB5UN & UT5AA SSB Handbook
There was a Book Of The Books in early 1970's - "Amateur Radio SSB Equipment" by S. Bunimovich (UB5UN) and L. Yailenko (UT5AA). Funny, but this book can be found in a common pirate's shack as well as in an Extra-class (1-st xUSSR category) HAM one. Yes, xUSSR pirates used AM only (mainly?), but this book was a great source of knowledge about tubes, transmitting equipment etc for everyone who been proud to heat The Ether.
There is a huge pile of a very complex things that described so comprehensible in this book, such as Phase Shift SSB Modulators, complete Transmitters, SSB Receiver's features, Dynamic Biasing and much more, but it is too hard work for me to translate all of those great articles and I decided to start with exposition of pair of a Ground Grid Linear Amplifiers - so simple, not so powerful, but namely these amplifiers was most popular in 1970's. Thought, every xUSSR HAM made one of these amplifiers and used one with a great success.
As for me, I did :)

Pair of GU-50 Tubes in The Grounded-Grid Amplifier. Blueprint.
"1-st Category Amplifier"
This amplifier can be used for SSB as well as for AM and CW amplification without any switching. With 200 watt of input power (legal limit in USSR) output power is 120-130 watt.

Amplifier utilises pair of GU-50 pentodes in grounded-all-grids circuit. Tubes works as a high gain non-biased triodes.
In virtue of using grounded-all-grids circuit amplifier is so cheap and can be easily made and tuned up. Futhermore, both bias and screen voltages are needles in a such design.
Because of indirect heating, it is possible to avoid a filament choke usage - there are no problems on the 14Mc band, but if your signal source on the 28Mc band can't offer enough power, it should be a good choice to feed a heaters through a little chocke.

Input impedance of this amplifier is 50-70 Ohm, that's why it is possible to feed one using equal impedance coaxial. (In fact it's wrong - there is something by 90-110 Ohm, not less, so that three or four tubes in parallel was much more common circuit. Not for extra power, only for impedance matching ;)

If you want to get only 200mA of a plate current with 1200V of plate voltage, it is enough to feed this amplifier using only 7-10 watt source. There is so small initial plate current, no more than several mA. Input power can be peaked up to 400 watts from pair of GU-50 without overheating, because average input power in such situation have to be around 200 watts (meant "not exceed legal limit")

Cathode choke "Dp1" 300-500uH have to be enough for 200-250mA cathode current. Chokes "Dp2" and "Dp3" used for prevention of oscillation on the UHF and contains 10 turns of enameled wire on the 1W resistor each. Plate choke "Dr4" (250mA) have to be a good performer on the all HF bands.
Serial network L2C5 have to be tuned to the local TV center frequency. With enough shielding and insulation from 220v AC input, this amplifier works practically without any TVI.

GK-71 in a Grounded-Grid Amplifier. Blueprint.
"Powerful GG amplifier"
In this amplifier works powerful RF pentode GK-71, all three grids directly connected to the ground.

There is only 3A current is needful for the heater, therefore a filament choke is not a big deal. The choke winding is 75 turns of pair of 1.5mm wire closewound on the foursquare block insulator 40x40mm. L1 coil has 3 turns of 5mm brass tubing; diameter 40mm, lenght 30mm. Variable L2 has a 12mH maximum. Input impedance is nearly equal to 200 Ohm. It is necessary to use a Pi-network circuit between transmitter and this amplifier. Initial plate current is 10-20mA at 1.5kV of plate voltage. This amplifier is so linear.

If you want to obtain plate current around 140mA from one GK-71 tube (210W input power at 1.5kV), you have to use only 15-20W source. If you need 300mA, you have to enlarge feeding power up to 60-80W. (It's good for a book. In a real world these amplifiers has been used in such manner: 2-3kV plate voltage, 300mA or just as much as possible plate current, big load of reserved tubes. GK-71 tube has a massive graphite anode inside, so main problem was a melted glass)
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Mike said...

Have anything in that book on using a GU5B in a amp? Can't find much info on it. Want to use that tube in a amp.

Mike -

Andy Nechaevsky UR3WA said...

no, there was no GU5B data in the HAM handbooks because of power limitations in S.U. - 200W output legal limit is slightly less than 6kW of this tube ;) But we've used to use GU5B anyway - mostly in contests, with high risk to lose license.

amadeus said...



Anonymous said...

Where can I find a copy of "AmateurRadio SSB Equipment" by S. Bunimovich (UB5UN)"


Andy Nechaevsky UR3WA said...


Direct link: (you have to have the DejaView software installed)

73! UU1CC

Anonymous said...

Thanks for the Link!

Would you happen to know the value of L1 and its tap on the "1-st Category Amplifier". Cant seem to find that info.

Thanks again!

Andy Nechaevsky UR3WA said...

..any kind of variable inductor, for example (I've used that one years ago, 70mm diameter, 85mm coil length, 40 turns, vernier). But it would be much better to use another coil on the 20m-10m bands.