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9A6C Croatia flag Croatia

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Ham since 1973, first callsign YU2RVS in 1976, followed by YU2OO, 4N2OO, 9A2OO and finally 9A6C. Work almost exclusively CW, except on VHF/UHF where some SSB is a must. Like HF/VHF contests, building amplifiers and antennas.


Tour guide through the title photo:


UP: HM HF PA 2xQB4/1100 (<1 500W); MFJ864/GI7b 6m PA/TS590S; 30A PS/E73M stackmatch/HM antenna switch; 15A PS


DOWN: DAIWA CN101L/TS930SAT; T2X control box/HV PS for 6m PA; XV144/HL160


My favourite logger is DXlog by 9A5K, supports more contests than I am aware of. ETM8 keyer is used in daily CW work.

Some bragging about my HB amps:

Interior of my HF amplifier. Basic design provided by YU1AW, but the arrangement of components in RF compartment should have been wiser - my fault...Needed some refinement...Plate voltage is 4 kV DC unloaded. Power output 1200-1500 W, band and mains voltage dependent.

So, new arrangement in output circuit now looks as follows:


You see that two RF chokes have changed position. It was necessary to move them further away from tubes, beacuse excessive heat caused melting of the material that suports chokes. Output relay has been replaced with the new silent one, and the old one is now used to ad extra 500 pF to C2 in PI filter (spot the red wire left of the bandswitch segment). Also, bandswitch has been detached from the front panel/ground as it arced...see the carbonized ceramic distancer between band switch segments on the left side. Untill 20 MHz all was cool, on 21 MHz&UP severe arcing occured between 80 m contact and left bolt that was connecting switch to the front panel when output rose above 700W. Don't ask me why... guess the punishment by some major QRP force...

Try to avoid surplus parts from your junk box and get yourself properly dimensioned and crafted parts for your amplifier if you can afford it . Maybe  you get rid of some P.I.T.A, unlike meangry.

Finally, 12 and 17 m bands were checked on 15 and 10 m positions. Tuning is sharp, but there is power, so...don't push too hard. 30 m is doing fine on its own bandswitch position.



Small 6m amplifier with single GI7b in test  position is shown above. Plate voltage 2.5 kV DC unloaded, power output 500W max. Original design by YU1AW had to be modified, since C1 in PI tank had too high starting capacity and consequently 2 turns had to be removed from the coil, resulting in 4.5 instead 6.5 turns. Also, input circuit was changed to "T" (single trimmer C&2 coils)  instead of YU1AW's original circuit. This is how it looks from above:

On the cover of the RF deck there is another 80x80 mm blower taken from some comp PSU to enhance air flow, note its reflection on the shiny black cover. Hope it will not melt during a contestfrown.

Separete HV PS offers a possibility to use it with another amplifier of similar power range. Beware of HV! Security trick is that HV PS can be activated from RF unit only, but take care - you live only once. And die, too.


My first 6m amplifier was constructed back in 2000. This early effort was graciously enhanced by Mike G3MY who supplied crucial data about coils and capacitors of plate circuit. I was proud enough to write an article about my next project with 2xGI7b, which you can find here: http://www.uksmg.org/content/poormanskwamp.htm.


Hand drawn schematic diagram is here:

C3 in plate PI-L circuit is best if home made as a flapper or rotary disc, since most of available HF surplus transmitting capacitors have too high starting capacity. Two tubes also contribute their C to the circuit as well. I used rotary discs of 60 mm diameter and distance betwen plates was around 5 mm, which should be some 5-6 pF. RFP2 is used in filament circuit of GI7b and was wound with Cu enameled wire thick enough to stand filament current of both tubes. Not critical. What really matters is to provide some air flow over cathodes, otherwise entire amplifier box will get too warm to touch, even if in receiving mode only.

6M amplifiers are simple and easy to construct. Specially if you are lucky. If you don't rely on luck - get yourself MFJ259B or another antenna analyser of similar range. Check F1FRV web page to learn more on its advantageous use in amplifier business. Saves lot of time and makes you stronger much faster. DX will appreciate that, you band mates might have a different opinion. But that's expected, so - go for it!


Next amplifier was crafted by 9A2HA more than 30 years ago. As you can see, it utilises a pair of  GK71 tubes (russian equivalent to 813) and some surplus parts (including a case itselfsmiley). It was out of use for more than a decade after its owner passed away, so when power was turned ON, a white smoke came out from HV PS in a separate boxcrying. All electrolytics had to be replaced (originals were made by TESLA factory in Czec republic with a gum tap onatopwink, luckily they didn't explode).

Since the original amplifier circuit had a bias voltage on grids and after grid PS blew, I decided to ground all grids directly and added ZX6.2 zener diode to provide bias and some idle current. TNX to Marcel YO6PMX for usefull tips on this onewink. Note a piece of aluminium sheet that carries ZX6.2 below white resistor on top left of photo. It cools ZX6.2 - important!

Original amp was made before WARC/160m bands became available at this part of universe,  but since heavy-duty bandswitch with six positions from ancient US ARMY BC panel was already inside, I added 30 m band (not shown in photo).

Power measurement showed 900 W on 80/20 m, 1000W on 40/30m and 600W on 15/10 m. Not bad for an oldtimer with most of parts used older than meyes. GK71's seem to be pretty jolly after all these years...

Great article about building 2xGK71 amplifier by OK1AMF can be found here: http://ok1amf.sweb.cz/konstrukce/PA2xGK71/PA_2xGK71.htm.

OM6BB also has a great compilation of different amps with 2xGK71 here: http://om6bb.bab.sk/files/Koncove%20stupne/KClanky/GP710001.pdf


Antenna status at JN73WS:

APRIL 2016:

- Inverted V's on 40&80m, appex at 10 m above ground

- Ground plane with 12 sloping radials on 40 m

- Ground plane for 30 m with 2 sloping radials.

40m gp with inverted V's in background

30m gp on a rooftop





I don't collect qsl cards, but if you need mine - let me know during a qso or via e mail. I  will send my card via bureau.


Don't send your card via bureau, I don't need it.




In spite of all, I do have my own qsl cards and send them away, hi. If you bureau service is not fast enough, send a card directly to my home address with SAE and 2$ enclosed. Use plain white envelopes, try to avoid air-mail striped ones if you can.


I still have a bunch of my old 9A2OO qsl cards and in case someone needs it, just e mail me.


I don't use LoTW or eQSL, sorry. It is paper only, one way or another.


Also, due to the inconvenience, I don't follow QRZ.COM logbook anymore, so if you need any confirmation of our qso, please refer to above - TNX.


Now active exclusively from JN73WS on both HF&VHF.


Sometimes I go portable to JN73XS for VHF/UHF reasons.


Activities from other locations are also possible, and in case of VHF&up qso, correct locator will be noted, as well as appropriate IOTA or CI references in case of island activities.



7460618 Last modified: 2016-07-23 16:08:47, 10784 bytes

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QRZ Logbook Summary for - 9A6C
Latest Contacts for 9A6C at QRZ.com
dedateband mode grid Country op
I0CMD 2014-01-19 40m CW JN61fo Italy MARIO CARUSO
DJ0AJ 2014-01-19 40m CW JO31jf Germany Ekrem Sulejmani
PA3EYK 2014-01-18 40m CW JO32bd Netherlands L PFAFF
OE7WRH 2014-01-18 40m CW JN77nm Austria Werner Winkler
G0ORC 2014-01-05 40M CW IO93ga England Vince Shirley
YU1TY 2014-01-04 40m CW KN14ho Serbia Ljubisa Trnkic
KA8G 2014-01-03 40m CW en80wc United States Dave
NP3K 2014-01-03 40M CW EM90fd United States CHARLES M ABRAHAMSON
K1RDG 2014-01-03 40m CW FN31id United States RICHARD D GRINALDS
DM3ZM 2014-01-01 40m CW JO61xu Germany Harald Siewert
N3JFD 2014-01-01 40m CW FN00ag United States John F Donovan
9A3VV 2013-12-22 40m CW JN65sk Croatia Damir Justra
IW5DLY 2013-12-22 40m CW JN53ku Italy CLAUDIO BALDI
HA1RJ 2013-12-22 40m CW JN87uq Hungary ANDRAS Pohl
IZ3XEF 2013-12-22 40m CW JN55mk Italy Ivo Camerlengo

Book Totals: 315 qso's   314 confirmed Get a free logbook at QRZ.COM

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