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Old 11th Nov 2005, 11:48 pm   #1
adibrook
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Default My attempt at a TRF

All this talk about TRF's and regens has really motivated me to try and build one. After all, theyre supposed to be simple. So, earlier today i went to Wilcos and bought a baking tray (hhhm i mean shassis ) ).

Normally when i do thigns like that i do abit and then get bored and go do something else. But for some reason i was motivated today, so i managed to nearly build one. All thats left is the wiring round the pentode regen detector thing.

Hers a couple of pics.

(BTW you may notice that thers a 6SN7 there...but thers supposed to be a 6SJ7. Thats only there because i wanted to make sure the valve plugged in ok, and thats the only octal i had handy).

The bad quality pic has the tuning coil (vanish still abit wet!) on it. I wount it on the inside tube of a toilet roll (classic!) and used very thi wire scavanged from a transformer.

Anyway, i hope to finish the wiring tomorrow and maybe fire it up.

The brass stud sticking out of the shassis is the tuning cap. Its the only place i could put it. Abit un-othodox maybe, but i dont mind. I dont think i'll bother with any kind of scale or anythign, just a knob.

There will also be a volume, reaction and possible tone pot sticking out the front.

i'm pretty impressed. Normally it takes me longer to do stuff like this.
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Old 12th Nov 2005, 10:16 am   #2
Neil Purling
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Default Re: My attempt at a TRF

Please post a few more pictures when you get it finished.
Please tell us where you got the circuit from.
Its a good idea to use the roasting tray, you can drill through the lip to mount the chassis in a case.
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Old 12th Nov 2005, 1:19 pm   #3
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Default Re: My attempt at a TRF

Hello Adi,
I am VERY impressed with your construction. It looks really great and what a wizard idea to use that baking tray. I think you may be presented with an 'easy cooking guide' by the shop that sells these items! They probably think you are burning holes in them....Wish I had thought of your idea 40 years ago. Keep us informed. Regards JOHN.
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Old 12th Nov 2005, 3:10 pm   #4
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Default Re: My attempt at a TRF

Oh, yeah. Baking trays are great as shassis's.

The best ones by far are aluminium ones. The 1st shassis i made was made out of an aluminium loaf tin. It's great. Easy to file into perfect holes to fit valves.

However, to my great dispair, wilkos have turned allt heir bakign trays into sheet steel! It's absolutly horrible to work with. Files dont cut it, they just bend it. It's thin, flimsy, and snaps too easily. When cutting the valve holes, i had to resort to ripping it with needle-noses!

The only other place that sells aluminium baking tins is the Cooking Shop, but i REALLY dont want to pay 16.99 for a baking tin! Wilkos do them for 4.49. But why did they switch to steel

I suppose the people at Wilkos must think i'm a very strange person. A person with a big leather coat long hair and big leather boots that buys 20m of doorbell cable and a baking tray every few days.

hehehe

Ok, i'm nearly done wiring everything.

One question. is it possible to control the 6V6's volume by controlling the voltage on the 2nd grid? Thesame way as ''reaction'' control is achieved by controllign the pentodes 2nd grid? That way i dont have to put any pots in the AF signal path, which means less wiring which is good for stability and generally good.
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Old 12th Nov 2005, 8:54 pm   #5
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Default Re: My attempt at a TRF

There was one of the Practical Wireless "blueprint" sets from the 50s built on a loaf tin (deeper sides for mounting the controls).

EDIT
A brief trawl of my files shows it to be the "International Shortwave Two" of April 1962, a battery set using 1T4 and 1S4, and it includes coil winding details. This is an A2-ish sheet, but if anyone is interested, PM me, and I'll scan it in sections and post it on my site.

Jim.
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Old 12th Nov 2005, 9:07 pm   #6
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Default Re: My attempt at a TRF

Your TRF looks neater than my attempts at making radios/amplifiers from my accumulation of valves. My projects were all made on a home-made 'breadboard' of MDF with panel-pins driven into it to act as points to solder components and wire-links (stolen from mains cables) between! Quite crude, but fun nevertheless!

Good-luck with your continuing construction projects. If you end up like me, a TV (and camera) will be an eventual construction aim! Uni does get in the way a little though!

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Old 12th Nov 2005, 9:10 pm   #7
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Default Re: My attempt at a TRF

Quote:
Originally Posted by jim_beacon
A brief trawl of my files shows it to be the "International Shortwave Two" of April 1962, a battery set using 1T4 and 1S4, and it includes coil winding details. This is an A2-ish sheet, but if anyone is interested, PM me, and I'll scan it in sections and post it on my site.

Jim.
I'd be interested Jim specially the coil details

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Old 12th Nov 2005, 10:08 pm   #8
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Default Re: My attempt at a TRF

Yeah. It would be very interasting to see the schematic and coil details.

Update on the TRF:

Bad news i'm afraid. I fired it up today, and the output transformer decided to die!

It was my only single-ended o/p tranny (appart from one in my Alba radio, but i dont want to scavange it). It came from a cheap ''cardbord'' record player (series heated el84 with heaters tapped from turntable motor) so i think it was a pretty poor quality unit.

However it did work on my amps and stuff.

It's definetly the transformer, since igt has full ht on one side and nothign on the other.

UUUUUGH it was goign so well.

Oh, well.

This is when a high impeadence earpiece would have come in handy. With one of them i would have been able to test the radio regardless of o/p transformer being dead.

Hey...isnt a high impeadence earpiece just a piezo-electric speaker? Thesame as found in cheap toys and alarm clocks? I have some of them...
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Old 12th Nov 2005, 10:41 pm   #9
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Default Re: My attempt at a TRF

Hello again Adi,
I will sort you out a transformer and drop it in the post maybe tomorrow. I have loads of odd output types that will suit your purpose. Leave the 6V6 screen connected to H.T. and I think you will find that the reaction control will have enough range to control the volume. Its a start and can be improved when its up and running.
Regards. JOHN.
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Old 13th Nov 2005, 3:10 am   #10
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Default Re: My attempt at a TRF

Thanks!

Appart from the o/p tranny i think its pretty much finished.

I stuck a dial lamp holder on the shassis too. It doesnt really light anythgin in particular, but i suppose it's a pilot light. Since i used a 12v bulb it's got a soft orange glow and not white light.

I put some bananna sockets on the font, only to realise that they hit the tuning cap when yoy turn it. So now it has a couple of bolt heads there. They look ok, and if you didnt know you probably wouldnt guess that theyre just there to cover up holes.

The PSU fires up allright, all voltages look normal, ht at about 320v (ish).

The regen detector (6SJ7) has a 1M pot for regen control at the moment. I didnt have a 50k, but i'll stick a 50k pot and a 220k fixed resistor when i get them.

I think it's anode resistor had to be 330k, since i'm out of 220's!

I'm pretty proud of this project. I's gotto be the 1st time ever i actually wired soemthign neatly! I'll put up some pic tomorrow
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Old 13th Nov 2005, 4:28 pm   #11
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Default Re: My attempt at a TRF

Hello Adi,
I admire your enthusiasm, it reminds me how I used to be in 1961. You can only learn by mistakes and I cannot tell you the things I did messing around with old telly's and other electrical goodies. We used to have 15amp 2 pin sockets in our Edwardian house and it took all but a street tram to blow the fuses ! [RCD..What the hells that !]
I packed up the transformer this morning with a few valves you might find useful. The EF91, EF92, EF95 and 6X4 [EZ90] are new. The 6BW6 which is the B9A version of the octal 6V6 is used but should be ok, the 6AT6 [EBC90] and 6AU6 are similar.
You made me open up a right can of worms looking for those bits in the summer house. I have never seen so much junk and unearthed quite a number of items I didn't know I had. I was concerned that if slipped on an old tube of MS4 grease and broke my leg I would not be discovered till the New Year......If you destroy your tuning cap I noticed a couple on some old gram chassis.
Mind how you go. Regards JOHN.
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Old 14th Nov 2005, 12:44 am   #12
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Default Re: My attempt at a TRF

Thanks! That will be very usefull!

Today i went down the local 1 shop and bought a pack of 2 window alarms. They are very simple, contained in a little case about the size of a lighter. They have a magnetic reed switch, oscillator and a piezo speaker.

I ripped the PCB and stuff out, and soldered the tiny ceramic speaker leads to the battery terminals (with batteries removed). Then i soldered doorbell wire to thesame battery terminals, and poked them out of a hole where the power switch used to be (with a knot to keep them there). I soldered them to the battery terminals to anchor them, since the cables from the speaker itself were very thin.

Anyway, what i ended up with is a high impeadence Xtal earpiece. With the case reassembled it's probbaly quiet safe too.

I tested it with a little DAF96 amp built on a proto-bord with 6 9V's as a power supply, and it seemed to work ok.

Anyway, now comes the cool part. I connected a 100K resistor across the blown O/P transformer, and the connected my Xtal speaker across that.

I actually herd two station! Both were french, and wever very very weak, and were accompanied by wierd whistling and stuff, but the main thign is it worked!

It's in no way perfect yet, but it IS a workign radio reciever.

I think it may have been very weak because of my coil. It was a bogroll coil, but the ariel primery and secondery were wound with about 5mm gap in between. I think people suggested winding them one on the other, wheras i wound them next to each other.

Also the bogroll tube was abit deformed.

I think maybe an RF preamp would be usefull here. I could stick in a 6SN7, with one side being an RF preamp and one side being an AF preamp. (i'v decided only to use octals in this radio...next one will be all noval).
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Old 14th Nov 2005, 8:52 pm   #13
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Default Re: My attempt at a TRF

Hi Adi,
I put the transformer and bits in the post this morning. I think you may get a better result with the transformer fitted in place of the earpiece. Try leaving the 100K in place and connect your earpiece from the anode via a small cap say .047 to chassis. Maybe a glance at your circuit will be useful for further information. Your R.F. stage is not recommended at the moment. The one valve detector should give a good result on its own. Your coil should also be o.k. even if its a bit distorted. Keep us informed!
Regards. JOHN.
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Old 14th Nov 2005, 10:30 pm   #14
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Default Re: My attempt at a TRF

Ok. Hers the circuit. It's basically the pentode detector that was posted in another thred with the 6v6 and associated components ripped out of one of my amp attempts.

Looking forward to recieveing the o/p transformer.

Any suggestions about the circuit?

I think thers somethign abit wrong with something. The reaction control seems to recieve weak french at both extremes of the pot but nothign in the middle. Also, after only getting one station with my PYE tuning cap, i decided to paralell it's 2nd gang that i ahvnt used. That improved thigns abit, but still only a couple of stations.

I'm using about 3-4meters of wire on a washing line as an ariel. I dont really have any more wire...yet.

The stations are very weak and have whistles. I dont quiet know what that means...maybe isntability?

Hopefully doing what you said to the earpiece will improve volume. Thanks.
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Old 14th Nov 2005, 11:41 pm   #15
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Default Re: My attempt at a TRF

WOOPS forgot to upload the schematic!

OOh, this is cool. I used that speaker arrangement and i actually herd a station that was loud enough to make out what the guy was saying. It was spanish.

Here are a couple of pics.

I'v fitted a ''dial lamp'' to the top, connected tot he rectifiers heater supply. It has no purpuse really, since thers no dial as such, but it looks good.

Sorry i couldnt get a good pic of the underside. the tuning cap kept reflecting the flash too much. You can see the holes in the front, and the 6v6's bodged grid resistor, which is double bodged since it's been bypassed with wire. Thats only temporery tho.

i think this set may even work...
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Old 14th Nov 2005, 11:48 pm   #16
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Default Re: My attempt at a TRF

Hi Adi you seem to be missing a screen feed resistor for the 6V6, for some reason 22K springs to mind here.

Decouple it to ground with a .01 as well.

Otherwise the 6v6 is running balls out all the time......

Cheers
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Old 15th Nov 2005, 12:09 am   #17
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Default Re: My attempt at a TRF

Another suggestion Adi, is that you place a 100pf or thereabouts cap in parallel with the 100k resistor on g1 of the 6V6 valve, this should help to reduce any rf getting into the 6V6.
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Old 15th Nov 2005, 12:46 am   #18
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Default Re: My attempt at a TRF

I think someone else on this thread suggested connecting the 6v6's 2nd grid straight to HT.

The 6v6's 2nd grid resistor used to be the 2nd pot, but then i bodged in a fixer resistor (the one in the pic that looks like a bodge with bare wires wrapped round the terminals). However after more advice i bypassed it with wire.

In all my amps i used a 22k with a 20uf cap to ground for the 6v6's grid supply.

I'll see what happens when i get the o/p transformer. Then i can make refinments.

I think maybe hthe best option would be to have a pot for the 6v6's grid vltage, with a cap to round as well for decoupling. that would amke a volume control...
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Old 10th Jan 2006, 7:42 pm   #19
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Default Re: My attempt at a TRF

in adibrook's TRF the bogroll tube is horizontally mounted onto the chassis.
Maybe the close proximity of all that metal will have a negative influence on the coil.
I intend to mount mine vertically.
In mine the design is the sketch by heatercathodeshort.
I had varnished a bogroll to stiffen it and I have wound 100 turns for the aerial input and given it a dose of varnish to fix the winding in place.
I place a sleeve of paper onto that and wind 65 turns, tapped at 5 turns.
The 'secondary' of 65 turns is the reaction and tuning coil. It is to be movable over the primary for best stability and volume balance.
Give heatercathodeshort's coil design a try and see if it improves your set.
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