Showing posts with label Valves. Show all posts
Showing posts with label Valves. Show all posts

6N7 Tube QRP Power Amplifier - One Rainy Day DIY Project

QRP 6N7 Tube Amplifier
Once upon a time I'd decided to join a Big Guns Gang and made a Super-Duper Powerful Vacuum Tube QRP amplifier for my 800mW QRPP homebrew telegraph vacuum tube transceiver "3T" (I promise to write a separate article or two about this three tube transceiver project later). It was not an easy decision to me because for that legendary time I'd almost a year used the QRPP power of less than a watt, but there was a rainy spring day, I've called CQ again and again without any takers and, at very last, somebody took over my only rock bound frequency. "That's all" - I said - "Enough!" ..and turned on my Soldering Iron.
Let me describe the scheme. Grounded-Grid design has been chosen because it is simple, easy to matching to coaxial impedance, provides the necessary level of amplification and typically requires no neutralization. After several experiments with triodes and double triodes I'd chose a 6N7S (6H7C) valve - Russian glass shaped version of well known 6N7 vacuum tube. I know that there was a 6N7G and 6N7GT American glass tubes, but as I heard these ones was not as common as metal 6N7.

6P3 (6П3) Beam Power Tetrode

6P3, 6P3S, 6P3S-E vacuum tubes

6L6 vacuum tube has been introduced by Radio Corporation of America in July 1936 and since 1937 it began to be produced in the USSR on equipment provided by RCA. For the first time it was usual metal 6L6 , but later was chosen glass bulb design in order to avoid overheating, so just before the WWII tube factories started to produce 6P3 (6П3) valves (left on photo), which was actually Soviet version of 6L6-GB tube.

After the forties, design has been changed (center tube on the photo) and the new one got additional "S" mark, which meant "Oktal" according to the post-war standard specification. There was some modifications such as 6P3S-E (6П3С-Е) (at the right on the photo) and 6P3S-EV (6П3С-ЕВ). I heard a lot of controversial stories about these extra letters, but according to the GOST it is Durability (E) and Reliability (V), so 6P3S-EV is just a high mechanical quality version of general 6P3S (6П3С) with warranted lifetime, probably military or industrial purpose. As for claimed electrical parameters, these 6P3S-E (6П3С-Е) and 6P3S-EV (6П3С-ЕВ) tubes has less current and voltage deviations than common 6P3S but according to my subjective opinion WWII 6P3 tube was a best performer in this family.

Naturally, 6P3 tube has always been one of the most popular in a variety of radio enthusiasts, it can be found in a Hi-End audio amplifier as well as in a HAM-Radio transmitter. BTW, not only HAM-Radio - it was and it is The Legendary Tube of the xUSSR Radio Pirates. Every Pirate Newbie starts with "The Whistle" - classical simple one 6P3S tube AM transmitter and so remarkable that a main web site of these guys is http://6P3S.ru

6P7S (6П7С) Sweep Tube

6P7S Sweep Tube
6P7S (6П7С) TV sweep tubes, as their western sisters 6BG6 was used as a horizontal driver in some early black'n'white TV sets. In fact, this tube is not a direct 6BG6 clone, it is an octal modification of G-807 tube, which one was soviet clone of famous 807. Interesting, that both 6P7S and 6BG6 tubes has the same pinout and nearly the same characteristics.
I heard that 6BG6 valves sounds much better than 6P7S in audio devices and that 6P7S is worthless audio tube, much worse than G-807 and 6P3S ones. At the other hand, I heard that 6P7S has a beautiful clear treble sound, much better than 6P3S. I'm not quite sure - it's just rumours.
As for me, 6P7S is a good choice if you have to put something more powerful than 6P3S (6L6) into the octal socket. Strangely, but 6P7S tubes are rarely used in HAM-radio (compared with G-807 and 6P3S).

GK-71 (ГК-71) Power Pentode

GK-71 (ГК-71) POWER RF PENTODE
GK-71 (ГК-71) is a somewhat similar (but not the same) to the famous 813 by RCA. There was another soviet replica of RCA 813 - GU-13.
GK-71 (ГК-71) has a narrower frequency range and a slightly less gain than, say, GU-13 tube, but there are some advantages - it was dirt-cheap and has a terrific endurance (resultant of massive graphite anode block and durable heavy-duty construction).
Possible, GK-71 was the most popular power tube in the AM pirate's anti-society. I'm not quite sure, I have no statistical data of pirate's preferences, but all of my unsocial friends was a GK-71 boosters.
At the other hand, this power pentode was a "Full Legal Limit" tube to the HAM Radio amateurs and one GK-71 final have to be approved without power measuring. I've heard rumours about the one GK-71 tube multy-megawatters, asbestos glove for quick tube replacement etcetera, but reality is slightly less wondrous - 350 watts from one tube without overheating, up to 450-500 watts if you are out-and-outer.

GU-50 (ГУ-50) Power Pentode

xUSSR GU-50 (ГУ-50) Tube
GU-50 (ГУ-50, folklore HAM name "poltinnik" meant "half-a-buc") was an universal, most common xUSSR power tube from the 50's up to the present days. It could be found in an every technical shop everywhere and was so inexpensive, in an usual TV-set's tubes price range. So funny, but sockets for those halfbucs was so rare and priced much more.
These power pentodes has been used as a transceiver final (one or pair of ones in parallel), in a modulator for the more powerful tube in AM transmitters, in a driver stages and (when SSB times comes) in the most common general class amplifier - three (or four) GU50 in parallel with all grids connected to the ground.
GU-50 is russian version of WWII Luftwaffe LS 50 general purpose HF power pentode by Telefunken, also known as RL 12 P 50 tube in Wermacht's transmitters. Main difference between russian and german versions - socket construction and dimentions, so I'm not quite sure that it is possible to use russian GU-50 as a spare part for a vintage german transmitter.
There are several other members in this family, such as DDR SRS 552 M tube, SL 152 (~12.6V filament) and EL 152 (~6.3V), but I don't know any more about these tubes, only that these tubes exists.