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[Sticky] Project: VRAT Minimalist Superhet Radio.

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Andrewausfa
(@andrewausfa)
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Please count me in, sounds an excellent idea Chris. I've not done any valve construction projects before.

Andrew

 
Posted : 22/09/2013 11:41 am
crustytv
(@crustytv)
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That's five on the project team, list updated.

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Posted : 22/09/2013 11:56 am
Westcliff
(@westcliff)
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I'd like to join in too. The only thing I have made so far is a fuzz pedal, which does not work. No valve-based building experience at all.

I do have a sufficiency of old parts though, enough to build most of a set. My personal preference would not be to use new parts if old ones are available, but that's just my point of view.

Gus.

 
Posted : 22/09/2013 9:16 pm
crustytv
(@crustytv)
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I'd like to join in too.
Gus.

Hi Gus,

I've added you to the project team, six now.

Chris

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Posted : 23/09/2013 1:32 am
Anonymous
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But if this became popular supplies of old parts for restoration would be badly raided.

I can only support use of old parts in "one off" ventures. For multiple builds new parts or at least very very common parts have to be used.

I would class these as temporary builds. They are just as easily dismantled if the parts are needed for more important projects.

Al

 
Posted : 23/09/2013 2:19 am
sideband
(@sideband)
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I would class these as temporary builds. They are just as easily dismantled if the parts are needed for more important projects.

Al

Yes that's exactly the point! It's how we all started.

Rich

 
Posted : 23/09/2013 9:41 am
Anonymous
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Perhaps it would be an idea to establish what the valves are we will be using then we can all have a look at our "spares" to see what we have. What ever we use it would be handy if they were very common types to give every one the chance of already having them in their spares stock.

I have dozens of octal rf pentodes

Cheers
Mike

 
Posted : 23/09/2013 10:55 am
sideband
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Perhaps it would be an idea to establish what the valves are we will be using then we can all have a look at our "spares" to see what we have.

That thought had crossed my mind. If the radio to be built is similar to the circuit originally posted, then I suggest that, for newbies at least, similar valves should be used. My main reason for suggesting this is that the circuit obviously works with the valves shown. A person new to the hobby trying to use octals or other types and then having no luck will be uncertain as to whether it's something they are doing wrong or parts they are using are unsuitable.

Rich

 
Posted : 23/09/2013 12:05 pm
boyblue
(@boyblue)
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Hi All , I,m in too. The last valve thing I built was a Mullard 5/10. Michael, watch you don't burn that high horse with your soldering iron !

Peter

 
Posted : 23/09/2013 12:42 pm
Till Eulenspiegel
(@till)
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We don't want a strictly standard design, the little Italian receiver sets out the basic concept. Personly I dont like the use of the OA70 germainum diode as the detector, that type of detector damps the tuned circuit. A better arangement would be a leaky grid detector with reaction. Other types of detector are the anode bend type and the infinite impeadance detector, it resembles a cathode follower. Both these detectors impose no load on the tuned circuit but I believe they require a reasonable level of signal drive to work properly.
Here's an idea. Why not kick off by building a simple TRF receiver, just two valves, detector and output. Get it going and later on modify it to become a superhet.

Till Eulenspiegel.

 
Posted : 23/09/2013 12:45 pm
crustytv
(@crustytv)
Posts: 11905
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Hi All , I,m in too. The last valve thing I built was a Mullard 5/10. Michael, watch you don't burn that high horse with your soldering iron !

Peter

Peter, added you to the team :aad now standing a 7 viewtopic.php?f=3&t=6469&p=67055#p67055

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Posted : 23/09/2013 12:48 pm
Stitch
(@stitch)
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....
Here's an idea. Why not kick off by building a simple TRF receiver, just two valves, detector and output. Get it going and later on modify it to become a superhet.

Till Eulenspiegel.

I like that idea :aad

Chris, I'm still interested if that's ok?

John

valveradios.com

 
Posted : 23/09/2013 2:40 pm
crustytv
(@crustytv)
Posts: 11905
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Hi John,

sorry I missed your hand going up, I've added you to the team list.

Chris

P.s.

To all Project Team

I have created a place holder on the main site https://www.radios-tv.co.uk/?q=node/190 this will take a high level reporting view of the progress. Leading to final features on each and every radio that gets built from this project. Hopefully a few words to accompany the set from each constructor on how they found the whole process, highs N lows etc.

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Posted : 23/09/2013 2:46 pm
Terrykc
(@terrykc)
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Surely such a project should feature a generic design which each individual can use with whatever components he/she has or can easily obtain?

What difference does it make if one person adopts a B9A approach using ECH81, EF85, EBC81 & EL84 whilst someone else builds an Octal version with ECH35, EF39, EBC33 & EL33 and yet another uses 6K8, 6K7, 6Q7 & 6L6?

OK, these are ful blown superhet designs I'm referring to but I'm sure you get the drift ...

Amongst all this squabbling, one little nugget from Michael seems to have been overlooked:

... Each IFT can be a pair of miniature/pocket Transistor Radio MW ferrite coils mounted in an alloy 200ml drinks can ...

This seems like an excellent idea but, perhaps, I can go one better ...

Why not use two IF transformers from such a radio back to back to form a single tuned high impedance IFT like this?

(No drinks can required!)

Afterthought ... small batches of TOKO inductors seem to turn up from time to time, often at very attractive prices. Suitably matched in pairs, quite a few combinations may be possible, although you might need an old TOKO list to tell you what's inside the cans!

When all else fails, read the instructions

 
Posted : 23/09/2013 4:18 pm
Anonymous
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Common Guys, lets have a virtual group hug and get on together. I am looking forward to it.
Mike

 
Posted : 23/09/2013 6:12 pm
Till Eulenspiegel
(@till)
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Found this scrap Regentone radio chassis upstairs. The front end will be OK. This set employs an ECH42 as the frequency changer. Next stage is chose a 6.3 volt triode pentode, the ECL83 might be a better choice because it has separate cathodes.
Let's find out if this simple superhet circuit is viable.

Till Eulenspiegel.

 
Posted : 23/09/2013 6:13 pm
Andrewausfa
(@andrewausfa)
Posts: 206
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I'm very much looking forward to this project and I'll also express my thanks to the gents taking the time to suggest what to make.

I had a look through my limited boxes of bits last night and the only thing I'm immediately short of are IFT's. I have a quite a few 1970s transistor TV ones but none for radio. Also had a look through my valves and I found a rectifier to use and some reflex klystrons which I'm sure will work great :bba :aae

Andrew

 
Posted : 23/09/2013 7:38 pm
Anonymous
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I seem to have loads of TV valves like PCL82, 84 etc. but no ECL80's unless I rob one from my newly acquired KB record player.
Mike

 
Posted : 23/09/2013 9:17 pm
EDDINNING
(@eddinning)
Posts: 208
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Hi Gents, I will second Til's idea. It may be best to build a simple 1 valve TRF, possibly powered by as little as 30V, with a virtually 100% success rate; then move on to the minimalist superhet using the same valve and coils (or at least all the windings on them now).
This was certainly the idea of Camm and others in their constructional series, to build confidence in the first time builder before going on to a more complex project.

Ed

 
Posted : 23/09/2013 10:06 pm
sideband
(@sideband)
Posts: 4222
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Further to what Trevor has just said, some negative posts have been removed. The project is going ahead and details will be available soon. We want everyone to have fun and hopefully gain some useful experience (and a working radio)! It's likely that most of the parts will be 'junk box' parts but don't worry too much if you only run to a few resistors and capacitors. There are plenty of VRATS who have boxes of bits and pieces and can donate coils, tuning gangs and other parts.

I'm not sure what the two instigators (Trevor and Till) have in mind but one suggestion has been to start with a TRF, get that working and then add other stages. Maybe there will be more than one circuit and you'll have a choice. Whatever they decide, you'll have fun! :aad

I'm very much looking forward to this project. Also had a look through my valves and I found a rectifier to use and some reflex klystrons which I'm sure will work great :bba

Andrew

Some great valves there Andrew but I think a Klystron is a little OTT.....! :aaj Then again Premier did use a small transmitting valve as output in one of their kits so..... :aaq

Rich

 
Posted : 24/09/2013 12:07 am
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