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Author Topic: 40M QRP AM  (Read 7246 times)
VE3LYX
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Posts: 813




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« on: November 14, 2011, 02:01:52 PM »

I started the project last year. Using a 1920s radio cabinet I laid it out and mounted the sockets for coils and tubes. It was to be a single control Rx TX. I got talked out of it a couple of times (too hard) and got sidetracked once or twice but it is up and running. 4 tubes , two 12sl7s ad two 50L6s  A pair in the rx and a matching pair in the TX. Rx is basically The Powerhouse Two Tuber from 1966 Pop Elec. The Tx is a Harltey VFO (grid cathode ground style)in one half of its 12sl7 and it is coupled to the 50L6 control grid with a 100 pf'r. The other half is a modulator feeding the screen of the 50L6 controled by a pot and a neon lamp in series. The output is a standard tank circuit. Voltage is 160 volts B +. The modulator is driven by a ww2 navy carbon mic in a battery audio transformer circuit. The set works good but lacks power so I built a small Pa , a stand alone unit to boost the level on the wattmeter. It is still under a watt but it works well. It had its first QSO sunday. 180 miles as the crow flies. I hang around 7120 for Canuck QSOs and 7290 for international. Eventually I would like around 4 to 6 watts output but for now I am just enjoying the fruits of my labour.
Don VE3LYx
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AD6KA
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Posts: 2243




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« Reply #1 on: November 14, 2011, 04:46:03 PM »

Hey Don!

Your project sounds first rate.
Can you share some photos of it by
posting them at one of the image hosting
websites such as Photobucket? It's free.

http://photobucket.com/

73, Ken  AD6KA
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VE3LYX
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Posts: 813




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« Reply #2 on: November 15, 2011, 07:50:24 AM »

Ill try. Here is a peek behind the panel

« Last Edit: November 15, 2011, 08:06:09 AM by VE3LYX » Logged
K0OD
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Posts: 3013




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« Reply #3 on: November 15, 2011, 01:57:42 PM »

"Panzer Freq?"  Is that the "tank" circuit?

http://s1236.photobucket.com/albums/ff449/Dolmetsch/?action=view&current=amrig1.jpg
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VE3LYX
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Posts: 813




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« Reply #4 on: November 15, 2011, 05:01:17 PM »

It is. Tank Frequency actually.  I discovered yesterday that the vfo and the rx detector (reflex regen) tune from 3.6 to 13.2mhz. The tank in the final doesnt but only because it has a 100pf variable capacitor instead of a 365 pf like the rx and tx (shared dual gang) I am going to pad it with a 220 and see if it will tune 3.6 as well. If so i think i will just buy a new single gang 365 for it. The final tube is only at 160 volts so arcing should not be a problem. The current one is a wide space high voltage from a industrial HF amplifier.
Anyway Strom is line power on AC, Zuruck is regeneration. (Literally return). Sprech % is speach percent or modiulation percent. It is a neon lamp in the screen modulation circiut and is very useful for watching you have enuf modulation in comparison to carrier.  Sprechen kontrol is modulation control. Laut is volume or loud for the RX. It isnt perfect yet but it does work quite well. I change it bit by bit till I am happy. The screen modulation system is from Bob Weaver's Am broadcaster design and is to me a brilliant system. Audio is quite good. I may play away till I get it all how I want then do a complete rebuild. We shall see. As I try this and change that is gets a few battle scars. I use it as an AM exciter to drive a homebrew 6v6 PA. If it has a fault it is that it could use better power but because it worked so well I choose an outboard amp rather than risk ruining a good thing. I did flog it for a few days and got some improvement but a PA is so easy to build it seemed a shame to mess with a good working exciter. The tx works great. You can set it so the carrier drops out if idling and it comes back on as soon as you speak like a vox circuit sort of . Currently I have it set so when I squeeze the mic talk handle the click is enuf to light the carrier. It doesnt drop out till I let go of the handle then although would if I sat there not speaking for awhile. .
The VFO is a slight rewirk of the rx 's regen detector which is basically an underpowered osc when in regen mode. It is a very very simple circuit but is rock stable. You can actually touch the main tuning variable cap and there is no wobble at all. It is a hartley circuit but a grid hartley instead of a plate hartley if you understand what I mean.  (grid, cathode centretap, ground) I have come to respect that design. Marrying it to the screen modulation circuit was my own idea but it works well.  Don VE3LYX
« Last Edit: November 15, 2011, 05:07:31 PM by VE3LYX » Logged
VE3LYX
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Posts: 813




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« Reply #5 on: November 16, 2011, 08:39:57 PM »

365 pf for tank parelel circuit ordered and on its way. Played with PA tank Q today but gained nothing except experience.
don VE3LYX
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WD6GLA
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Posts: 87




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« Reply #6 on: November 19, 2011, 10:46:18 PM »

Great work Don , 

Its good to see hams who still experiment and build their own gear .  As long as there are those kind of people there is still hope for this hobby .

I sniffed around your site and you've done some interesting stuff with radio projects and with cars too .  Thumbs up from an old lifelong mechanic and tinkerer . 

73
Bob Tadlock  N7BDY
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VE3LYX
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Posts: 813




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« Reply #7 on: November 21, 2011, 09:14:59 AM »

Thanks,
I have had a blast so far.
Don VE3LYX
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AD6KA
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Posts: 2243




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« Reply #8 on: November 23, 2011, 08:08:52 PM »

Wow, that is an AMAZING rig Don, BRAVO! 

For those of us not as smart in design nor
handy with tools as Don, Small Wonder Labs
offers the "Retro-40" 40m AM QRP kit.
Also available for 80m.

http://smallwonderlabs.com/

Certainly not nearly in the same league with Don's work
but will get you on the air....and have some
of your own fun building it.

$69 bucks plus shipping for the "board and parts"
version sounds like a heck of a lot of fun to me.

Gonna write me a note to Santa Clause..... Grin
73, Ken  AD6KA
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VE3LYX
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Posts: 813




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« Reply #9 on: November 23, 2011, 08:19:24 PM »

Well that looks awfully complicated to me but I am sure it would still be a lot of fun. Go for it. Speaking of AM I am tuned up and testing on 7141 all this week if anyone would care to try for a QSO or even a sig report.  I call everytime I am near the rig.
Don VE3LYX
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VE3LYX
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Posts: 813




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« Reply #10 on: November 25, 2011, 12:16:15 PM »

I will be testing tomorow on 7141 from time to time early morning through early afternoon. If anyone hears me a signal report would be nice. Don VE3LYX.
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