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Designing & Building a Vintage Style 3-valve TRF

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Re: Designing & Building a Vintage Style 3-valve TRF

Post by DavidW » Fri May 27, 2016 8:15 am

Another brilliant project Bob and, along with the scale model ships, I wonder how many hours are in your days,mine are set at the standard 24 but your time zone must have at least 36 hours to the day!

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Sun May 29, 2016 2:06 pm

I am now moving towards the final completion, but have had a few days off after getting fed up of it! This morning, I decided it was time to go back to it, but got "cold feet" about screwing everything down to my flashy polished wood base in its final configuration (in case it didn't work). So, I fitted all the component onto a rough board of the required size. Good job I didn't take a chance on using the posh board, as quite a few of the smaller components had to be juggled around to fit them in. I found I was also short of one capacitor holder for the 0.1uF screen decoupler on V1. This is the wired in yellow capacitor next to V1. I will make a proper mount later. Initially, I thought I would just wire the detector, and if that worked, add the output stage and then the RF stage. But on completing the wiring for the detector, I felt that I may as well push on and do the whole lot (patience running out). Anyway, it worked fine, although maybe not as loud as before. I found that adjusting the value of C1 in the aerial lead, I could regain the lost volume whilst still keeping a good degree of selectivity. Adjusting C1 may be having a positive effect by "trimming" the aerial which is wire in quite an unacceptable manner. It is thin, stranded, insulated bell wire stapled directly to the bungalow wall for a distance of eighteen feet. It then takes off to the top of the garage, and across to an eighteen feet-high flagpole. The total length of the aerial from where it leaves the wall is about 55 feet. I installed it using sheer guesswork. It had to be stapled to the wall, to get around the front and side of the bungalow in order to get a clear run to the top of the garage and across to the flagpole.
I am now all ready to transfer the receiver onto it polished board, but will probably take some time over this!
The HT and LT, incidentally, is fed in on the back panel via a 4 pin DIN plug!
Bob
Attachments
1 on rough board (Medium).JPG
1
2 on rough board (Medium).JPG
2
3 on rough board (Medium).JPG
3

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Tue May 31, 2016 1:27 pm

Racking my brains about what to put in the gap on the right hand side, to even up the controls, I finally decided on a tone control. This is a 50K pot in series with a .047uF capacitor, connected across the primary of the output transformer. It works very well. I am now ready for the transfer to the polished board and neat wiring.
Bob

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by crackle » Tue May 31, 2016 4:03 pm

I am eagerly waiting to see the finished radio.
Your photographs are very good do you use natural light or what.

Mike

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Tue May 31, 2016 5:42 pm

Thanks,
Yes, I use natural light. I never ever use flash. I photograph things in the conservatory that has a white, translucent top that diffuses the light. I have always found that flash ruins a photograph by the creation of harsh shadows.
I am pleased to see that the views for this build have now topped the 1,000 mark! :)
Bob

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Wed Jun 01, 2016 5:15 pm

I have now fitted the aluminium angles to the sides of the board, fitted the valve-holders, and wired in the filament circuit of the three valves. The back panel has also been fitted, and the power input socket wired in. The top brass rail on the board is the HT positive line. The bottom strip is the main earth line, and the centre one is the filament positive line. At this stage, I plugged in the batteries, and made sure that there was only two volts across the filament pins of all three valves, and full HT between the earth line and the HT positive line. The aerial capacitor has also been fitted and wired in. I had to make sure that the contacts were clear of the aluminium side strip.
Before I began transferring the components from the rough receiver, I photographed it from several angles for reference when rebuilding it on the polished base.
Bob
Attachments
2 (Medium).JPG
Started re-build

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Lloyd » Thu Jun 02, 2016 2:18 pm

Hi,

This is a fantastic project, I have built a valve superhet from scratch before, I based it on the circuit for a Cossor something or other, using different valves. It worked beautifully first time, but then I tidied up the chassis, and it never worked again! I must get back at it and get it working again. I actually made the chassis from a bit of plastic rectangular vent pipe left over from installing a cooker hood.

Regards,
Lloyd

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Thu Jun 02, 2016 3:15 pm

Yes, that is the problem. There is no real guarantee that the above will work after I have built it neatly. At the moment, I am adding new brass strip wiring, and double-checking everything as I go along. I am sticking as close as I can to the untidy working version. More images soon.
Bob

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Thu Jun 02, 2016 5:22 pm

I have now done a bit more wiring around V1 using polished brass strips. The brass bar along the inside top of the back panel is the negative feedback (reaction) line from the anode of V2 to the reaction coil.
Bob
Attachments
V1 wiring - Copy (Medium).JPG
V1 wiring started

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Fri Jun 03, 2016 1:13 pm

I have now fitted more wiring on the other side.
Bob
Attachments
More wiring (Medium).JPG
Mre wiring

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Sat Jun 04, 2016 5:04 pm

Quite a lot of progress has now been made. The main components and wiring are now complete. A lot of it was more of a light engineering exercise than radio. With brass strips and bridges, lots of nuts and bolts and solder tags. Close up images do not show it up to its best, as they highlight any defects. In actual fact, it looks a lot better than this when view normally!
I am beginning to get a bit "twitchy" now, as to whether it will function, or not, after all this work. Time will tell, but on the "home run" now.
Bob
Attachments
V1.JPG
V1 wiring
V2 V3.JPG
V2 V3 wiring
Main wiring.JPG
Main wiring

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Sun Jun 05, 2016 9:43 am

Becoming overcome with impatience, and curiosity as to whether it was going to work, or not, I wired in the two variable capacitors and output transformer with loose temporary wiring. Before testing it, I completed a few essential checks without the valves, but with the HT and LT plugged in. I confirmed that each valve-holder had only the required two volts on the filament sockets. With the meter positive on the earth line, I confirmed the presence of the 3 Volt grid bias on the grid of V3, also that HT was present on the anodes of V1, V2 and V3, and the screen grids of V1 and V3. On fitting the valves, and connecting aerial and earth, I found that although the set worked, the volume was low and the reaction did not work at all! I metered the windings on the base of the coil unit, and found they were open circuit. Removing the coil can, I checked the 100uH reaction choke and found it was OK. I removed the coil unit from the board, and found a broken wire underneath leading from the reaction choke to the connection terminal. I assume this must have happened when I tightened the nut up on top when fitting the solder tag. Replacing the coil, I found that the receiver was then working properly, with plenty of volume. I can now go ahead and make the wiring of the variable capacitors, output transformer and tone control permanent, safe in the knowledge that it will work!
Bob

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Sun Jun 05, 2016 4:40 pm

I have now fitted the tuning and reaction capacitors, and wired them up permanently. Again, I tested the set with the output transformer wired in loosely. The same as last time, it worked, but on very much reduced volume, with the reaction control working normally. A close inspection showed that I had forgotten to connect the first half of the tuning capacitor up, so the RF stage was not being tuned. When I connected it up, everything was working normally again. One strange thing that I noticed concerned the aluminium angle down the sides and across the front. These were just added to make it look better by hiding the rough edges of the baseboard. They are in electrical contact with each other, but nothing beyond that. When I had the tuning capacitor loose yesterday, it moved slightly when I was tuning the receiver in, and came into contact with the front aluminium angle. The volume rose by noticeable amount. I bore this in mind, and just carried on. Today when I tested it again with everything fixed in position. I again connected the angle to the tuning capacitor with a screwdriver, and the same thing happened. I double checked that the angles were completely isolated from the rest of the circuit, and they were. I cannot explain this, but may make a permanent link later! The big space on the right hand side is to take the final three components. The output transformer, tone control and tone capacitor, Completion is now very close.
Bob
Attachments
1 (Medium).JPG
1
2 (Medium).JPG
2
3 (Medium).JPG
3
4 (Medium).JPG
4
5 (Medium).JPG
5
6 (Medium).JPG
6

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Katie Bush » Sun Jun 05, 2016 5:25 pm

That is looking very nice now, Bob, and reminiscent of those modern build audio amps you can buy on eBay.. If you had the time, patience and nothing else to do for the rest of your life, you could probably make and sell these, and if anything like the prices asked for those amps, quite profitably.

Only thing - if you did, avoid terms like "retro" and "steampunk" - that would instantly shave a hundred off the final value!

Marion

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Sun Jun 05, 2016 5:45 pm

Thanks Marion.
I probably wont have the heart to part with it when it is finished! Anyway, it will allow me to test my quite large store of 1930s valves that I have had for years. Building a duplicate would be a lot easier now I know that the layout is OK. I really was getting quite worried that it may just burst into uncotrollable oscillation in its final form :ccf but it seems stable enough, and I am quite surprised at the performance. It guzzles less than 7mA on the HT. As the resistors are inside old fuses, it will allow me scope to fiddle with the values to some extent without taking it apart!
Bob

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by raditechman » Mon Jun 06, 2016 5:03 pm

At the beginning of this thread the ship RMS St Helena was mentioned.
The ship is leaving service soon and is as part of its farewell voyage is arriving in London tomorrow, 7th June 2016, it will be moored whist in London next to HMS Belfast. The ship will be in London for 3 days. Further details via the link below.

https://www.ianvisits.co.uk/blog/2016/0 ... ng-london/

John

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Mon Jun 06, 2016 5:35 pm

Thanks John. We were invited to the "do" but declined, bit too expensive in trains, hotels, taxis etc for a two hour reception! My wife & I sailed aboard her from early 1990 to late 1992 when I left the sea!
Bob
---------------------
Three Valve TRF
I completed it about half an hour ago, and it works beautifully! The only bit of surface wiring that defeated me was getting the two connections from the output transformer across to the loudspeaker jack socket. There was simply not enough room on top of the board. I drilled two holes next to the transformer. and two more close to the speaker jack socket. The wiring went underneath the board, and is held down with heavy tape! When I tested it, V1 was taking 1.2mA anode current, V2 1.2mA and V3 4mA, total 6.4mA when running on an HT of 100 Volts. I tried a very scabby looking W21 in place of V1 (SG215) and found the volume was rather louder. Because it was such a scruffy looking specimen, I laboriously scraped all the dirty grey metal coating off, and polished it up a bit! So there you have it, from my initial vague mental design to the completed receiver, via many changes and trial and error methods. I have no doubt that the more learned amongst you could just design it on paper, and produce a working receiver without having to alter anything, but that sort of thing is beyond me! You will note that I have been very heavy with the polished brass, nuts and bolts etc. The only reason for this was that some time ago, I obtained a large quantity of brass strips on a car boot sale for a very low price, and a 1.5 kilo tin of 6ba brass nuts & bolts from Ebay, for a similar low price, and wanted to use some of them. I can now study the set at leisure, draw out the final circuit, and decide how it works! :bba
Bob
Attachments
1 (Medium).JPG
1
2 (Medium).JPG
2
3 (Medium).JPG
3
4 (Medium).JPG
4
5 (Medium).JPG
5

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by crackle » Mon Jun 06, 2016 6:52 pm

Hi Bob
Thanks for this thread, I have enjoyed following it. The result is a very smart looking radio with all the shiny bits.
Will you be polishing the tuning caps, I feel they look a little dirty compared to the rest of the lovely work you have done.
I wish everybody added photos to their threads in as good quality as you have.

Mike

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Mon Jun 06, 2016 6:58 pm

The capacitors were the cleanest I could find. I did think of respraying them with grey matt car primer, but it would have meant quite a lot of masking of the vanes etc. May get round to it eventually. I was just pleased to get it finished, as it is very hot & sweaty today, over 100 degrees F outside! (Preston)
Bob

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by crackle » Mon Jun 06, 2016 7:46 pm

I have heard that some people put them into a dish washer and they come out looking clean.
Mike

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Sparks » Thu Jun 16, 2016 5:50 pm

FINAL DEVELOPMENT
Old vintage valves (SG215, HL2 and KT2) can be quite expensive these days, so I thought I would make three base adapters to see if it worked with more modern valves. The bases were taken from old, faulty valves, two B4 bases and one B5 base. The first B4 was to adapt V1 from an SG215 screen grid valve to a 1T4, B7G type that is far cheaper and easier to obtain. A B7G valve holder was mounted in the old B4 base and the pins connected accordingly. As the SG215 had an anode top cap, I fitted the anode connection to the side of the base within easy reach of the original anode lead. V2 is another 1T4, this time with the screen grid strapped to the anode, running it as a triode. The V3 output valve is a DL96. All three adapters have a 10 Ohm dropping resistor in the positive filament wiring inside the bases. This allows the set to still be run on 2 Volts LT. The HT was reduced to about 85 Volts, and the set still performs well!
This is as far as I will take it. Although there were a considerable number of views, it generated very little comment or discussion, and this was rather disappointing. It appears that very few vintage radio enthusiasts these days enter into the realms of vintage radio design and construction in the old style! Such is life!
Bob
Attachments
TRF With 1T4s & DL96 (Large).JPG
With more modern valves

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Aerodyne » Thu Jun 16, 2016 7:31 pm

Bob, despite the fact that the thread generated little comment, it certainly proved of great interest to many - including me, even though I did not make a comment, feeling anything I might add would be superfluous and that your work and descriptions stood perfectly by themselves.
A very well presented and described project, Bob, up to your usual high standard.
If anyone is wondering why I've not been posting much of late, have not been active due to pressing health problems. I am typing this having arrived back from Papworth earlier today. The twin procedures went well, I think, but my goodness - incredibly painful. Trust me to need something off the beaten track!
Anyway, Bob, all credit to you.
Tony

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by crackle » Thu Jun 16, 2016 7:43 pm

Dont get disheartened Bob, it seems that over the last year or so people have stopped commenting and are tending to just hover in the background .. something has changed. I have noticed the same tendency in my restoration threads.
But your high quality construction methods demonstrated here makes this a unique project. One that others could also try, and is one of the best threads I have seen on this vintage radio forum in years.

Mike

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by Lloyd » Thu Jun 16, 2016 7:55 pm

It looks fantastic! :thumb

I very much enjoyed following your thread, and it has re-kindled my interest in building a set myself, after my failed superhet (which I must have another stab at!). Shame that it didn't spark more discussion, I'm far from capable of designing my own circuit from scratch, but can work from copying bits of circuits from elsewhere and modifying them to work together.

Regards,
Lloyd.

 
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Re: Designing & Building a Vintage Style 3-valve TRF

Post by sideband » Thu Jun 16, 2016 8:21 pm

Sparks wrote:This is as far as I will take it. Although there were a considerable number of views, it generated very little comment or discussion, and this was rather disappointing. It appears that very few vintage radio enthusiasts these days enter into the realms of vintage radio design and construction in the old style! Such is life!
Bob


Don't be disheartened Bob! I enjoy home construction when in the mood. Your radio is a work of art and was an enjoyable read. I didn't comment mainly because I've never undertaken anything like recreating a vintage-style set....plus I don't have the time being still employed! I followed it every step of the way though.

It was exactly the same a few years ago when Till suggested a 'minimalist Superhet' for home construction. He (mainly) and I set about deciding the best circuit and began building the set and posting the results. We both ended up with good working sets of slightly differing design but as far as I know, only Crackle built a set and finished it off in a very attractive cabinet.

Overall response was disappointing and we've not repeated the exercise.

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