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Old 20th Nov 2016, 8:39 am   #1
its ur aerial
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Default Top Band Hybrid Transmitter.

I am keen to get on a local 160 Net, and want to build a 10 -15 Watt AM TX with a Valve PA, possible with, a 807 PA, but this is not critical, other options would be a 6bw6, which I believe is just a small 6V6 ?
The rest of the TX, VFO Driver and Modulator, I was going to make solid state.
The VFO would be a couple of BC108`s Driving a BFY51, would this have sufficient out put to drive a valve PA ? Also regarding the solid state modulator can any one see any serious problems with the idear.
All comments appreciated. 73`s G6HZG
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Old 20th Nov 2016, 10:15 am   #2
Ed_Dinning
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Default Re: Top Band Hybrid Transmitter.

There was a good homebrew design in PW in the late 50's/ 60's.
It was the cover feature, but I can't find the edition, some of the other members may remember it.

Ed
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Old 20th Nov 2016, 10:42 am   #3
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Default Re: Top Band Hybrid Transmitter.

It was a common project, every magazine had one every few years.

10-15W means 807 rather than 6V6 or 6BW6. Top band doesn't need the top cap advantage, so a 6L6 would do.

A pair of 6V6 or 6L6 would make a matching modulator. One of the Woden modulation transformers would do the business but be a bit large for this power level.

In 1960's / 1970's RSGB handbooks there is a mobile transmitter as well as transistor modulator that would fill the bill... along with the winding recipe for the mod transformer. You'd probably want to convert the design to silicon, though. Otherwise most designs for hifi/PA amps in the genuine 50W-100W class would be fine.

BEWARE that old AM TX designs were rated in DC input power. 150W input was seen as producing 400WPEP. Modern SSB TX are rated in watts PEP. The aviation transmitter I designed was rated in carrier power so a 16 to 20W TX produces 60-80W PEP and your modulator has to be able to drive the peaks.

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Old 20th Nov 2016, 1:14 pm   #4
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Default Re: Top Band Hybrid Transmitter.

All valve would be a nice classic tx. There was a Woden UM0 on ebay sold for £11.49 which seems reasonable. I have pdf of data sheets for that series of transformers, just pm me. Another idea might be to use the Pye Westminster W30am mod transformer. A 30W am mobile with easily 80% mod to a QQV06-40 PA valve driven by a pair of 2n3055. Not sure of the valve load impedance though. Someone on here might have such a transformer for reasonable price if you ask? If you want to save time, also get the matching audio pcb from same rig? Can't remembet if it also had a pair of RCA 40250 as drivers for the 2N3055 mounted on a small heatsink. Depends how much original construction you want to do.
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Old 20th Nov 2016, 3:36 pm   #5
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Default Re: Top Band Hybrid Transmitter.

Quote:
Originally Posted by Radio Wrangler View Post
It was a common project, every magazine had one every few years.
Yes, almost always valve, a few solid state later on, but I don't recall a hybrid.

My recollection is the use of the 6BW6 or 5763 RF output, with something like an ECF80 as oscillator/buffer. There was one design in PW for a very compact rig using a single ELL80 as output for the modulator.

Although Pye's RTs were often hybrid, the one attempt I made to build homebrew hybrid proved... "problematic" .

B

Last edited by Bazz4CQJ; 20th Nov 2016 at 3:42 pm.
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Old 20th Nov 2016, 4:10 pm   #6
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Default Re: Top Band Hybrid Transmitter.

I recall this one by Noble and Pratt in Feb '62 Short Wave Magazine. You could replace the VFO and buffer with transistorised circuits if you feel it appropriate. 5763 PA and 2 x 6BW6 modulator.

http://www.g4dmp.co.uk/articles/SWM-02-62.pdf

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Old 20th Nov 2016, 4:30 pm   #7
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Default Re: Top Band Hybrid Transmitter.

A friend of mine once made a copy of the Codar AT5 and used a mains transformer with dual 115V windings to act as modulation transformer. It worked very well.
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Old 20th Nov 2016, 7:01 pm   #8
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Default Re: Top Band Hybrid Transmitter.

Firstly, have you looked at what parts you already have...if any? If using valve modulator, if no proper mod transformrr available, as stated, a mains transformer might suit, as might an ht choke. Do some research. Radio constructor, Short wave mag and Practical wireless all worth researching, 1950s to say lateish 1960s. F G Rayer (G3OGR) being a prolific author.
You need to consider cost of some of the valves, as audio users also seek them! However, push pull 6bw6 should be cheapish. I think I have some 5763/6ch6/6cl6 that were sometimes specified for rf. Just cost of postage really if needed.
It is years since I built such tx, my first being 50 years ago! 807 pa with a lovely blue glow inside which varied as you tuned the pi tank. As not licensed, it was OF COURSE into a light bulb dummy load!
Nice to see some interest in such home brew rigs. I wish you well in your quest.
I will have a look round see if I have any pdf articles I can email to you, can't promise anything though.
Rob
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Old 12th Dec 2016, 9:12 am   #9
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Default

Top band was always my fave rate band but now I live in Thailand and we only have a very short section of the band. But sadly there is so much noise over here it makes it impossible to use the band at all. Very sad as I would love to make a valve transmitter again.

I would love to see the schematic for this.

Paul G0MIH/HS0ZLQ
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Old 13th Feb 2017, 11:04 am   #10
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Default Re: Top Band Hybrid Transmitter.

the pw dart by dobbs and turner 1 November 1983. no valves though. pierce ei7ka
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Old 16th Feb 2017, 10:18 am   #11
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Default Re: Top Band Hybrid Transmitter.

Back when I was building valve AM transmitters for er..'MF' duty, I had no easy access to 'proper' RF valves, but at low frequencies like Topband, anything will do. I pressed EL84, EL34, 6V6 etc into service with good results. Choke modulation was frequently used with another similar valve doing the audio work.
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Old 16th Feb 2017, 11:39 am   #12
John M0GLN
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Default Re: Top Band Hybrid Transmitter.

I've just finished building an 80M AM all valve transmitter and used this modulator,

http://ekladata.com/ddX2c-NG42DyDMPd..._cq_jun_56.pdf

with a 6AG7 crystal oscillator and 807 final. I haven't used it on air yet but it looks good into a dummy load.

John
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Old 29th Mar 2017, 1:23 pm   #13
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Default Re: Top Band Hybrid Transmitter.

Quote:
Originally Posted by Ed_Dinning View Post
There was a good homebrew design in PW in the late 50's/ 60's.
It was the cover feature, but I can't find the edition, some of the other members may remember it.
There was a later, simple solid state project called the PW "Chatterbox"....

Here is a link I found for that project, if it's of interest.

http://www.robkalmeijer.nl/techniek/...e19/index.html

Regards,
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Old 29th Mar 2017, 3:53 pm   #14
Ian - G4JQT
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Default Re: Top Band Hybrid Transmitter.

I built the Chatterbox. It needed some work on getting the modulation anywhere near decent (even after the modifications and updates) and they had a tendency for LF modulator instability. There was a mod to run it off 24V with a transformerless modulator. My mods were in Sprat and maybe the 24V mod was in PW, or Sprat.

But it's OK if you are prepared to work on it. Only produces about 5W of carrier, or 20W PEP if that makes it appear more attractive!

But to be honest I'd probably just copy a Codar AT5. They were a good compilation of all the standard AM/CW valve circuits at the time with some nice features. Even the mod transformer shouldn't be particularly hard to locate or substitute.

Ian
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