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6th Mar 2008, 5:57 am | #1 |
Heptode
Join Date: Jan 2007
Location: Parkes, NSW Australia
Posts: 877
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MATE AM transmitter
There have been some recent posts about low power AM transmitters used to broadcast proram material around the home.
I have built up a couple as designed by Peter Lankshear and described in an old issue of Electronics Australia. I attach a pdf of the project in case other members would like to give this worthwhile and satisfying project a go. Peter |
6th Mar 2008, 8:11 am | #2 |
Retired Dormant Member
Join Date: Mar 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 1,587
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Re: MATE AM transmitter
Thanks for the info Peter, I think I will have a play with one of these.
Mike |
6th Mar 2008, 3:09 pm | #3 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,580
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Re: MATE AM transmitter
Very interesting. I have a boxfull of ECC82's and the like. Now I've got something to use them in.
Rich.
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16th Mar 2008, 10:02 pm | #4 |
Octode
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
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Re: MATE AM transmitter
Hi all,
With the weather being crap all day and the missus out sailing I locked myself in the shed and built this little gadget I used the chassis and power supply from an old sig gen I had knocking about, I used the valves from the sig gen too, Two ECF80's. I used the pentode section of one as a preamp and then used the two triodes as the diagram suggests. The coil was a standard medium wave coil off of a ferrite rod which I wound 25 turns over the top for the tickler winding, I also retained the 500pf variable two gang cap from the sig gen to make variable tuning easy. I also stuck an EM84 in which gives an indication of how much modulation is taking place. The whole shibang works pretty well but the fidelity isn't as good as I would like (lack of response in the top end) I am half way through drawing the diagram in paint and will post when finished for those who are interested. Cheers Lee
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Lee |
16th Mar 2008, 11:11 pm | #5 |
Nonode
Join Date: May 2006
Location: St Albans, Herts, UK.
Posts: 2,193
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Re: MATE AM transmitter
Yes Lee. Very interested
Cheers,
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All the very best, Tas |
19th Mar 2008, 6:39 pm | #6 |
Octode
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
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Re: MATE AM transmitter
Hello again,
Crikey, I am having a busy week, anyway attatched is a file of the schematic of my version of the MATE. Cheers Lee
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Lee |
19th Mar 2008, 8:54 pm | #7 |
Octode
Join Date: Jul 2006
Location: Willand, Devon, UK.
Posts: 1,023
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Re: MATE AM transmitter
That's a super drawing there Lee, well done. If I ever get some spare time I will definitely have a go at making one of these.
cheers, Matty |
19th Mar 2008, 9:01 pm | #8 |
Retired Dormant Member
Join Date: Jun 2003
Location: Scunthorpe, UK
Posts: 154
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Re: MATE AM transmitter
Thanks Lee.
I was thinking about how to wire a pentode as a triode, which I should know & along came your excellent schematic. John. |
19th Mar 2008, 9:34 pm | #9 |
Retired Dormant Member
Join Date: Jun 2003
Location: Scunthorpe, UK
Posts: 154
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Re: MATE AM transmitter
Sorry!
V1a isn't wired as a triode. John |
19th Mar 2008, 9:38 pm | #10 | |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,972
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Re: MATE AM transmitter
Quote:
Triode wired means the screen grid is connected to the anode and the suppressor grid is connected to the cathode. In this case it wouldn't make much difference. Paul |
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19th Mar 2008, 9:40 pm | #11 |
Rest in Peace
Join Date: Jul 2004
Location: Dartford, Kent, UK.
Posts: 1,661
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Re: MATE AM transmitter
I built one of these more or less to the original design using a 6AT6 and ECC82 back in the 90s, it works very well if you keep it away from house wiring which tends to induce hum, but all designs I've tried do the same. .
Regards, Mick. |
19th Mar 2008, 10:33 pm | #12 |
Nonode
Join Date: May 2006
Location: St Albans, Herts, UK.
Posts: 2,193
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Re: MATE AM transmitter
Thanks Lee. I think I'll have to have a go at building it too.
Cheers,
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All the very best, Tas |
20th Mar 2008, 11:41 pm | #13 |
Heptode
Join Date: Jan 2007
Location: Parkes, NSW Australia
Posts: 877
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Re: MATE AM transmitter
I've built two two of these transmitters and both work pretty well. From memory I used a couple of 6SN7s, oh..and a 6V4 rectifier.
In Australia the US series of valves are more common. Peter |
23rd Mar 2008, 8:19 am | #14 |
Nonode
Join Date: Jun 2004
Location: Norwich, Norfolk, UK.
Posts: 2,543
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Re: MATE AM transmitter
Hi,
I need to wind the oscillator coil. Are both windings wound on in the same direction? David |
23rd Mar 2008, 8:59 am | #15 |
Heptode
Join Date: Jan 2007
Location: Parkes, NSW Australia
Posts: 877
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Re: MATE AM transmitter
I'm assuming so. I used an oscillator coil from and old chassis.
Peter |
25th Apr 2008, 2:44 pm | #16 |
Nonode
Join Date: Jun 2004
Location: Norwich, Norfolk, UK.
Posts: 2,543
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Re: MATE AM transmitter
I've made the transmitter, following the diagram as in post #1 as closely as possible.
It works quite well but it transmits louder and clearer once the mains is turned off. Even with the HT dropping below 100V it's still working really well Any ideas why? David |
25th Apr 2008, 6:10 pm | #17 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,518
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Re: MATE AM transmitter
I would think that you are undermodulating - as the ht drops the available modulation is more able to swing the anode volts of the transmitter.
Either make the audio side work harder, or make the RF side a little less powerful. how far is the transmitter from the radio - it could of course be desense due to the massive signal! Cheers Sean
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17th Jun 2008, 8:10 pm | #18 |
Dekatron
Join Date: Mar 2008
Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.)
Posts: 3,184
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Re: MATE AM transmitter
I fancy building one of these gadgets too and wondered if an EF80 could be used as the AF pre-amp? I know it's meant for RF circuits but it should work at AF. Or would it be better occupied as the final valve before the aerial, with an ECC82 for the first two stages? Also one of the above posts said that the circuit lacked treble, how could that be corrected?
I've tried one of those silly 2.4Ghz senders connected to the PU sockets of my radiogram in the hall but it's useless & swamps the wi-fi to the laptop so this little device sounds ideal. cheers de Pete
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17th Jun 2008, 8:30 pm | #19 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,972
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Re: MATE AM transmitter
This design will be very tolerant of valve types and a very wide range should work.
An EF80 should be OK in all positions, and the pinout is shared with a number of other suitable valves - EF85/EF89/EF183/EF184/6BW7/lots of others. Other very common junk box valve types which should work are EF91/6AM6 (B7G) and EF36/EF37/EF39/6K7/KTW63 (octal). You can just triode wire a pentode if you use it in the triode positions. Paul |
18th Jun 2008, 9:37 am | #20 |
Dekatron
Join Date: Mar 2008
Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.)
Posts: 3,184
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Re: MATE AM transmitter
Thanks for the info Paul, Just before we moved out here I got rid of dozens of EF80's but lurking deep among the boxes of stuff I did bring was a homebrew FM tuner with a few of 'em still living in it. Plus I've got a few telly valves too, handy if I ever get around to building an amp with a pair of PL81's
Cheers de Pete
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