MATE AM transmitter - UK Vintage Radio Repair and Restoration Discussion Forum

petervk2mlg · 6th Mar 2008, 5:57 am

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

MichaelR · 6th Mar 2008, 8:11 am

Thanks for the info Peter, I think I will have a play with one of these.

Mike

Sideband · 6th Mar 2008, 3:09 pm

Very interesting. I have a boxfull of ECC82's and the like. Now I've got something to use them in

.

Rich.

Hunts smoothing bomb · 16th Mar 2008, 10:02 pm

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

Tazman1966 · 16th Mar 2008, 11:11 pm

Yes Lee. Very interested

Cheers,

Hunts smoothing bomb · 19th Mar 2008, 6:39 pm

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

matthewhouse · 19th Mar 2008, 8:54 pm

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

johnn · 19th Mar 2008, 9:01 pm

Thanks Lee.
I was thinking about how to wire a pentode as a triode, which I should know & along came your excellent schematic.
John.

johnn · 19th Mar 2008, 9:34 pm

Sorry!
V1a isn't wired as a triode.
John

paulsherwin · 19th Mar 2008, 9:38 pm

Quote:

Originally Posted by johnn

Thanks Lee.
I was thinking about how to wire a pentode as a triode, which I should know & along came your excellent schematic.
John.

That pentode isn't wired as a triode, it's wired as a pentode

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

mickjjo · 19th Mar 2008, 9:40 pm

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.

Tazman1966 · 19th Mar 2008, 10:33 pm

Thanks Lee. I think I'll have to have a go at building it too.

Cheers,

petervk2mlg · 20th Mar 2008, 11:41 pm

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

Radio_Dave · 23rd Mar 2008, 8:19 am

Hi,

I need to wind the oscillator coil. Are both windings wound on in the same direction?

David

petervk2mlg · 23rd Mar 2008, 8:59 am

I'm assuming so. I used an oscillator coil from and old chassis.

Peter

Radio_Dave · 25th Apr 2008, 2:44 pm

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

Sean Williams · 25th Apr 2008, 6:10 pm

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

Tractorfan · 17th Jun 2008, 8:10 pm

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

paulsherwin · 17th Jun 2008, 8:30 pm

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

Tractorfan · 18th Jun 2008, 9:37 am

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

6th Mar 2008, 8:11 am	#2
MichaelR Retired Dormant Member Join Date: Mar 2006 Location: Sheffield, South Yorkshire, UK. Posts: 1,587	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
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,566	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. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

16th Mar 2008, 10:02 pm	#4
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	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 __________________ Lee

16th Mar 2008, 11:11 pm	#5
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: MATE AM transmitter Yes Lee. Very interested Cheers, __________________ All the very best, Tas

19th Mar 2008, 6:39 pm	#6
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	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 Attached Thumbnails __________________ Lee

19th Mar 2008, 8:54 pm	#7
matthewhouse Octode Join Date: Jul 2006 Location: Willand, Devon, UK. Posts: 1,023	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
johnn Retired Dormant Member Join Date: Jun 2003 Location: Scunthorpe, UK Posts: 154	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
johnn Retired Dormant Member Join Date: Jun 2003 Location: Scunthorpe, UK Posts: 154	Re: MATE AM transmitter Sorry! V1a isn't wired as a triode. John

19th Mar 2008, 9:40 pm	#11
mickjjo Rest in Peace Join Date: Jul 2004 Location: Dartford, Kent, UK. Posts: 1,661	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. Attached Thumbnails

19th Mar 2008, 10:33 pm	#12
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: MATE AM transmitter Thanks Lee. I think I'll have to have a go at building it too. Cheers, __________________ All the very best, Tas

20th Mar 2008, 11:41 pm	#13
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	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
Radio_Dave Nonode Join Date: Jun 2004 Location: Norwich, Norfolk, UK. Posts: 2,543	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
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	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
Radio_Dave Nonode Join Date: Jun 2004 Location: Norwich, Norfolk, UK. Posts: 2,543	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
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	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 __________________ Engineers make things work and have spare bits when finished

17th Jun 2008, 8:10 pm	#18
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,181	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 __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

17th Jun 2008, 8:30 pm	#19
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,928	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
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,181	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 __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."