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Old 12th Nov 2008, 10:11 pm   #1
HMV 1120
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Default Glowbugs.

Two simple CW xtal-control transmitters, each for the 40mb, that I have built over the last two nights. One is a home design using an EL90 that is to be used at our club room (henced supervised operation - will have to wait untill my intermediate to use it here) and the other is a kit-built design using a H7A (12K5) putting out approx 200mw (comparable to the Pixie QRP set) using a 12V power supply.

I was wondering if any forum members have operated similar sets and how they've got on?

The EL90 set - expected output around 1-1.5 watts with 250 DC on the plates. Now needs some tidy up work to keep fingers away from HT.
Filament provided by a single PP3. The crystal socket is an old valve base. This was built entirely from my scrap box, with the exception of the ceramic base. I have one spare (B7G size) should anyone want it.

http://i148.photobucket.com/albums/s...g/DSCF0572.jpg



The 12K5 'Hollow Pixie'. Both plates and filament use 12V DC. The crystal soldered in is 7.040KHZ. I might wind another coil and try it on 20mb as well

http://i148.photobucket.com/albums/s...g/DSCF0574.jpg
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Old 12th Nov 2008, 10:21 pm   #2
mickjjo
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Default Re: Glowbugs.

Quote:
Originally Posted by HMV 1120 View Post
Filament provided by a single PP3.
Impressive stuff! , But how do you get 450 milliamps for an EL90 heater out of a PP3?

Regards, Mick.
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Old 12th Nov 2008, 10:31 pm   #3
HMV 1120
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Default Re: Glowbugs.

I can't - simple answer! Instead the battery EMF drops it down to around 7.5V (fresh battery) and runs for around 3 hours or so. The heater glows quite bright for the first few hours of use. I assume that there is enough emission there for this set to work, but its all very experimental. I haven't built a PSU for it yet either, but I have an EZ81 tucked away for that. If I can find an old transformer I might be lucky enough to get one with a filament winding.

Regards, Robs
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Old 7th Dec 2008, 4:11 pm   #4
Norman Wells
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Default Re: Glowbugs.

Re Glowbugs
Astonishing construction technique ! Its a VERY long time since I saw a bread board hay-wired like that !! Norman Wells
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Old 8th Dec 2008, 1:42 am   #5
Alf
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Default Re: Glowbugs.

I like the use of the Fahnestock clip in the project, in fact, I'd like to see more outlets for this simple device, a very useful piece of equipment for breadboard design.
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Old 12th Dec 2008, 11:48 pm   #6
HMV 1120
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Default Re: Glowbugs.

Norman:

As you can see, I put an awful lot of thought into the planning....
Exposed wiring and HT are not a good mix, this set now has all live points covered up. A suitable DC PSU is next on the list.

Alf: Thankyou with regards the clips - I can't see why they are not more widely used! I have seperated the filament and voltage rails on this kit now and with 20-30vdc on the plate I can push output into the 300-450mW range (Yes - just under half a watt!)

I have made a handful of local contacts with this TX but it needs a decent antenna. With it able to operate off 12v I aim to do some portable working...

Regards, Robs
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