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It is easy to install 6E5 in place of oscillator tube because socket's pinout of this amazing valve is nearly the same to pinout of common 6J5 and 6C5 triodes.

So, you can replace these tubes with The Magic Eye without any soldering. But if you want to see The Legendary Green Glow, you have to apply some voltage to the Pin #6 (fluorescent screen)...

Experimental QRP transmitter by UB5DT, "Radio" magazine, April 1967

"Radio" magazine cover, April issue, 1967
For those of my friends tube radio builders, who asked me about "Soviet novice transmitter", "XUSSR QRP TX" (as it pronounced in telegraph),"something authentic, but not too complex" etc, such a RIG should be a good choice - easy to build and clearly adjustable design, small amount of widespread parts, a lot of potential operational fun (two possible output sockets, changeable configuration, very uncommon CW note, i believe). And, after all - a frumpish bald telephonist on the cover as a genuine sign of Soviet authenticity.

Experimental QRP Transmitter by I. Tsapiv (UB5DT):

This simple two-stage telegraph transmitter has been developed for a QRP experiments on the amateur HF bands.

The rock bound exciter on the 6П3С (6L6-GB) vacuum tube utilizes circuit known as the "Three-point" (or Tritet in common notation). The crystal controls the frequency of oscillation - 3510kc in this case. Signal output is taken from a separate tuned tank circuit L1C4 in the plate circuit of exciter; this tank should be tuned to 3510kc or 7020kc.

The second stage on the 6П7С (6BG6) tube acts as an amplifier or frequency multiplier (doubler or tripler) depends on an inductance of the L2 coil and bias voltage on the signal grid of this tube.
QRP Transmitter
If you would like to use this transmitter on 80m band as well as on 40m with a noticeable lowered power, you have to connect an antenna to the "A1" connector and pull the amplifier tube (6BG6) out from the socket. For the general power output on 7020kc and QRP operations on 14040kc and 21060kc that tube has to be back and antenna switched to the "A2" output connector.
Measured Power:
frequency single stage (6П3С) both stages
3510kc 8 W -
7020kc 3 W 18 W
14040kc - 6...8 W
21060kc - 1,5...2,5 W

Several interesting QSO's  has been obtained using this transmitter in October 1966. For example, UA0MX and K2AGU on 14Mc, and F9MC on 21Mc with a power level as low as 1.7 Watt.


Two Tubes QRP Transmitter Circuit

Coil Data:
#frequency, kcwinding typecoil formturnswire
L1 3510...7020 Single-layer 30mm 15 ø 0,5mm
L2 7020 Single-layer 20mm 31 ø 0,35mm
L2 14040 Air-wound, 50mm long 30mm 11 ø 1,0mm
L2 21060 Air-wound, 35mm long 30mm 6,5 ø 1,0mm

Experimental QRP Transmitter Parts

2 comments :

Anonymous said...

Hello !
The 6L6 is just a 6BG6G, with the anode connection carried at the socket. It allows, therefore, a cleaner layout when it comes to delivering the RF to the PA tube. What do you think ? My main TX is a MOPA, actually, with VFO + 2 aperiodic buffers added before the driver/multiplier. Actually is general coverage from 1.6 up to 15 Mhz, and with some improvements in the resonant circuits, I am planning to go up to 28 MHz. It is so stable and chirpless that I don't need modern gear. The VFO is made by a triode, and has both band switching and control grid keying. The 7MHz 4th harmonic on 28 MHz is very clean and stable. My MOPA is really not a compromise ad allows me radio traffic in CW with, practically, no any limitations!
73 de Cristiano, IZ3CQI

Andy Nechaevsky said...

Hi Cristiano and thank you for the comment.

I shouldn't say that, for example, 6BG6 is a less powerful version of 807 or, as you said, slightly different version of 6L6. It is not quite true - those tubes has a different purpose, construction, characterisics and so on. Sure, they are very close to each other, but not the similar ones.

It would be really interesting to read an article on your MOPA, to see the photo set or even the video about it. If you'll decide to write such an article, please drop a link here.

73! UU1CC