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VK7ZL
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« on: September 22, 2011, 10:05:05 PM » |
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I completed my 40M transmitter project about 3 months ago but forgot to upload the pictures. It is working well and audio reports are all good. I had to drop the HT down to 650V as it was driving the mod tranny too hard so the output power is down to about 60W.
Bob VK7ZL
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K1JJ
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"Let's go kayaking, Tommy!" - Yaz
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« Reply #1 on: September 22, 2011, 10:49:25 PM » |
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Cool looking homebrew rig, Bob.
I noticed the 40M toroidal tank coil. Does it run cool? I see Alpha uses them on 160 M (I think) in their linears.
60 watts is a respectable power on 40M AM. What modulator tubes are you using?
T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. Easily done in DSP.
Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."
There's nothing like an old dog.
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VK7ZL
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« Reply #2 on: September 22, 2011, 11:50:47 PM » |
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Tom
I used the wide toroid and there is no problem with heat at all.
The modulator is an ex Pye base station using a pair of 5/40's (6146 equiv) and they ran 50W in commercial service so the mod tranny would have have been designed to just do the job.
When I recapped the power supply I used 100uF in place of the original 8uF's which in turn pushed up the HT. The xmtr put out 80+W but the mod tranny complained bitterly when I tried to fully modulate it. I reduced the HT by changing the power supply from capacitor input to choke input.
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KA2DZT
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« Reply #3 on: September 23, 2011, 02:02:37 AM » |
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Bob,
Nice looking rig, nice neat layout.
Good luck with it.
Fred
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W7TFO
WTF-OVER in 7 land Dennis
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IN A TRIODE NO ONE CAN HEAR YOUR SCREEN
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« Reply #4 on: September 23, 2011, 02:34:21 AM » |
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GOOOOOOOOAL!  Unless you are not a soccer fan... Kudos! 73DG |
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Just pacing the Farady cage...
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KC9LKE
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« Reply #5 on: September 23, 2011, 07:18:10 AM » |
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Congratulations Bob on a very nice transmitter! Looking forward to a QSO  Best Regards Ted / KC9LKE |
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KM1H
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« Reply #6 on: September 23, 2011, 12:00:53 PM » |
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Several companies use toroids on 160 and 80 in the Pi and on all bands in the L at up to 3 x 3CX800 capability.
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flintstone mop
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« Reply #7 on: September 23, 2011, 07:20:32 PM » |
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Nice layout.........two 807's ready to make RF
Fred
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Fred KC4MOP
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W7TFO
WTF-OVER in 7 land Dennis
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IN A TRIODE NO ONE CAN HEAR YOUR SCREEN
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« Reply #8 on: September 23, 2011, 08:40:45 PM » |
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Nice layout.........two 807's ready to make RF
Fred
Look closely, they be 1625's with the 7-pin base. 73DG |
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Just pacing the Farady cage...
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KK4RF
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« Reply #9 on: September 24, 2011, 08:40:48 AM » |
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Bob,
Nice work! I like the toroidal inductor in the output pi-network. With air-wound inductors so expensive these days, I always wonder why we don't see more use of the toroids in these tube circuits. Just curious how many microhenries in that toroid and if you wanted to go onto 75 meters, would you basically double the amount? Lastly, if you could sometime, post your schematic. Again, nice work there. 73s, Marty, KK4RF, Suffolk, VA
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KM1H
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« Reply #10 on: September 24, 2011, 11:36:01 AM » |
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Lots of good stuff on this site including the Pi/Pi-L network design/analysis spreadsheet http://www.ifwtech.co.uk/g3sek/ |
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W3GMS
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« Reply #11 on: September 24, 2011, 11:43:09 AM » |
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Superb build Bob! Nice neat spacious layout and I like the mechanical placement.
Enjoy it!
Joe, W3GMS
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Simplicity is the Elegance of Design---W3GMS
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VK7ZL
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« Reply #12 on: September 25, 2011, 12:21:33 AM » |
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Thanks to everyone for their favourable comments. The circuit is below.
Bob
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