Hey all you good buddies, 10 4 and all that stuff...Chicken bander this week...

Got a phone call a week ago from a VK5 ham looking for a devoted 28mhz amplifier..Well, I completed it yesterday and ready to be sent off...This is one of my standard jobs using a pair of Russian GI-7B triodes along with an Antek toroidal HT transformer that delivers 2500vdc @ 600ma...I fired it up today and it easily gives 800 watts carrier output so has ample headroom for the VK 400 watt power limit...

Playing around with it this evening I find it also easily tunes up on the chicken band 27mhz right up to 29mhz ....I cheated a bit in the construction as I had a spare 50mhz chassis and front panel already completed so that gave me a head start....I used an old Hammalund WW2 tuning cap in the anode tuning and a shunted Millen cap for loading with some 1/4 inch plated stock for the coil...

Now I wouldn't purposely build a 27mhz amplifier but quite surprised how easy it is to do..:evil: The new owner takes delivery next week and now wants me to build him an 833A 196khz VLF amplifier...In VK we have an allocation down there apparently...I will let you all know when I start into that job, it's a challenge and I will have to source some information on VLF amplifiers....

Enjoy these pics...

Bob..VK3ZL..

That's a nice piece of work, Bob.

Our two area "leenyar" amplifier constructors (one of whom went SK a year ago this month) tip their hat to you. I don't recall the products of either of them ever looking quite that good.

Clean, neat buildt amps Bob.
Pity you don't live closer though...;)
Love the orange on the front, looks quite nice.

73,
Cor

BOB! DUDE! That is a sharp as hell mate!!!! Very sweet indeed!

Quote:

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Originally Posted by PA5COR

Clean, neat buildt amps Bob.
Pity you don't live closer though...;)
Love the orange on the front, looks quite nice.

73,
Cor

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Thanks Cor...I use vinyl auto pin striping to outline the front panels...This particular color is "Fluro Red" ..Quite effective...The paint is "Metallic Charcoal"...It has a fine glitter...These are my standard applications on my amplifiers...I always outline ZL RF Engineering, the year and the type of amplifier...Each amplifier has around $600 of new components, case etc so when I sell them for $1080, standard price I really make very little for my efforts...However, it is the pleasure I get making them which is the most important thing...

Bob..VK3ZL..

Bob, am I correct in assuming that you've built a switching-type HV power supply for your amp? If you have, care to impart some of the details of it's construction?

That's AWESOME Bob, I've never in my life seen a "CB leenyar" so professionally done! I don't know about that high power 196KHz amp, as far as I can see from here your LF band is this:

2200 metre band plan, 2200 meter band plan.

135.7 - 137.4 kHz Morse code (CW) only.

135.7 - 135.8 kHz International long distance (DX) communications window.

135.8 - 136.0 kHz Test transmissions and test beacons.

136.0 - 137.4 kHz Normal Morse code (CW) operation (centered on 136.5 kHz).

137.4 - 137.6 kHz Narrow band digital transmissions e.g. PSK (centered on 137.5 kHz)

137.6 - 137.8 kHz Slow Morse code (CW) transmissions e.g. QRSS.

The Aussie (Australian, Australia) 2200 metre band is 135.8 kHz – 137.9 kHz (0.135.8 MHz – 0.137.9 MHz) using narrow band modes of transmission (such as Morse code and narrow digital transmissions) with a maximum antenna radiated power of 1 Watt effective isotopic radiated power (1 Watt e.i.r.p.).

To achieve the legal antenna radiated power of 1 Watt EIRP with the normal low efficiency low frequency antenna it is necessary for the actual transmitter output power to be much higher than 1 Watt.

In January 2009 the Australian Radio Frequency Spectrum Plan was amended by the Australian Communications and Media Authority (ACMA) to create the first Low Frequency amateur radio band in Australia.

Low Frequency radio listeners can use free to download computer software to see on their computer very low power radio signals over large distances as well as radio signals under the noise.

This band was made available to radio amateurs worldwide in the International Telecommunications Union (ITU) World Radio Conference (WRC) in 2007.

From June 2009 the 135.7 kHz to 137.8 KHz band is available to all holders of the Australian Advanced Amateur radio license by applying to the Australian Communications and Media Authority (ACMA).

By the end of 2009 or in 2010 the ACMA will allow use of this band to all holders of the Australian Advanced Amateur radio license without the need for Amateur Radio Operators to specially apply.

Australia’s contribution to the successful worldwide adoption of a new amateur radio band in 2007.

Then there's this:

130 kHz – 190 kHz is the 1750 meter band (1750 metre band).

The Kiwi (New Zealand) 1750 metre band is 130 kHz – 190 kHz (0.130 MHz – 0.190 MHz) using all transmission modes with bandwidths under 6 kHz such as AM voice transmission, Narrow Band FM (NBFM voice transmission), SSB voice transmission, CW (Morse code) and narrow digital transmissions with a maximum antenna radiated power of 5 Watt effective isotopic radiated power (5 Watt e.i.r.p.).

Due to the low efficiency of low frequency antennas the actual transmitter output power is much higher than 5 Watts.

June 2009 New Zealand amateur radio frequency allocation plan.

http://www.nzart.org.nz/maps/2009/2009-bp1-2.pdf

Progress with Digital Modes and Techniques in New Zealand.

Click- NEW ZEALAND PROGRESS REPORT.

Incremental Frequency Keying IFK was first suggested by Steve Olney VK2ZTO and is seen in the Jason software (in the Italy section). DominoEX (IFK+) is a computer-based radio mode intended for simplex chat-mode (real time keyboard chat) operation on the lower frequency bands but is excellent from LF to VHF.

DominoEX allows perfect copy of 77 words per minute Morse code with 260 Hertz bandwidth

DominoEX is tolerant of drift and frequency error.

DominoEX has improved robustness in NVIS propagation conditions especially against multi-path effects that are common at night on low frequencies.

http://www.qsl.net/zl1bpu/DOMINO/Index.htm

http://www.qsl.net/zl1bpu/ZL2AFP

"I will have to source some information on VLF amplifiers."
It looks like you'll have to source information on VLF operation first?

G'day Warren, and thanks for all that info...Yes, it is strange territory for me...We have a few hams here some who have had a special permit for 196khz for more than 30 years...I used to listen to VK3ACA in Melbourne when I lived in Portland around 200 miles away...He always had a good signal...His antenna was a loaded T with a large wire top loading...The antenna loading coil at the bottom of the antenna was wound over a 12 gallon plastic garbage bin...Pretty primitive but surprisingly effective...Yes, he had a 1 watt ERP limit as far as I can remember....I

I will look into the ACMA site and look at their information...Can't say I am particularly keen to build this job but it may be an interesting experience....I know there are a few hazards around VLF amplifiers but can't remember the details...I think it has to do with stray RF etc....The ham who wants the job done has a good collection of old broadcast amplifier gear for components including some big edge wound inductors, caps etc...

I have a still crated up new TCA ex navy VLF 50 watt transmitter in my store shed somewhere...It is a shipboard unit weighing around 130 pounds...It has a big vacuum relay and many big inductors with lots of those old mica bolt down capacitors...The entire case and chassis is made from brass...I have never bothered uncrating it...These were available after the Vietnam war when the armed forces modified all their radio equipment...I even have the companion receiver as well....Junk..

jBob..VK3ZL..

Hi Carl, The hT supply is a straight Bridge rectifier..In this case I used an Antek AN800 toroidal tranny...It has two 800 volt windings which I series for around 2500 vdc output....The higher voltage is from my 264 volt mains into the transformers 220 volt primary....These transformers are only rated at 800va but the overall efficiency is good, much better than an IE type tranny..I can pull 800 watts output from the toroidal unit quite easily...There is around 80mfd of filter capacitance...These particular Antek transformers are used a lot by VK hams in VHF amplifiers especially for data work....

I have read quite a bit on switch mode HT supplies but I don't think I am prepared to try one...I believe that a few microwave oven manufacturers use them these days...I have tried using microwave tranny's in amplifiers with mixed results...For higher power output I have access to toroidal transformers up to 1.5kva rated...They are relatively cheap and very robust...Cost around AU$200 to have them made and posted....These are good for reliable 1kw output...These days I find it is much more efficient and easier to source all new components for my amplifiers rather than compromising with junkbox stuff although that is the way I built stuff for years...

I am not a commercial entity so my component costs are much higher than company's who manufacture radio gear..I just have a fascination for constructing my own amplifiers and do one off custom jobs for friends..Each job is a new learning experience and I can draw on my years of experience to make each one just a little better..It isn't the electronics that interest me all that much, rather, using my hands to create things...I also do quite a bit of wood turning, another creative hobby...I built my first lathe 20 years ago and hand forged all my own lathe chisel's and other accessories...These things keep me out of mischief...Jeannie runs all our gardens and is very passionate about it...I need permission these days before I am allowed to run a coax or any other RF application through the gardens which cover more than 1 acre...Between the two of us we have plenty to keep us contented...

Bob..VK3ZL..

Bob..VK3ZL..

Okay, Bob, thanks. I was fooled by that toroidal transformer. I'd never seen one used in a standard analog power supply but I know they're often used in switchers.

You do beautiful work. If I had the money, I'd commission you to build an HF amp for me in a heartbeat.