Just for fun!

Hi Trevor,

I keep seeing those components on eBay, and very much 'belt and braces' they appear to be.. I've always been fascinated by all the 'screwed to a plank' technology of those days, with the huge valve bases that just, well, literally screw down to a piece of wood, and the resistors as big as a triple "A" battery, coils as big as bean tins, and so on.

The nearest I ever got was building a crude crystal set onto an old kitchen tray

My granddad was the fellow who could build things and had loads of old books on self build kit, including things like; a washing machine, radios, home intercoms, and Lord know what, then the books on household repairs - they were a treasure trove of knowledge.. You'd get shot to bits nowadays if you tried some of things in those old books!

Marion

Is that copper laminate you've used for a chassis, Trevor?

Wouldn't plywood have been more authentic?

Marion, if you've never tried it, you don't know what you're missing!

Start off with a one valve TRF - you'll be astounded at how sensitive they can be with a decent aerial!

You may have to wind the coil yourself (or modify an existing one to add the reaction coil - an over-wind on a MW ferrite rod aerial is easy).

Of course, if you can find someone who's got a Repanco DRR2 stashed away, that would be ideal!

Circuitry is simple. When I built one, using a 1N5 (cheapest available!) I cheated in the headphone department. High impedance headphones cost £2 - £3 - a veritable fortune! - but a surplus low impedance headphone cost 3s 9d, so I fitted an output transformer salvaged from an old set and it worked splendidly!

Great stuff.

I will get back shortly to my Rod Pentode version of the combination of a couple of the 1934 Ever Ready design.

At night China uses the old R. Lux. 208 transmitter on MW.

Various European SW sites, inc I think even on occasion UK! Strongest Day time SW most of the time.

Times changed since Cold War eh?

Energy Drink minicans and Shh! Tonic water mini cans (shorter) are alloy rather than steel so good to shield coils.

Can needs to have 1 coil radius space between sides and coil and a bit more than one coil diameter from ends.

I was always amazed at how good these simple one and two-valvers really were. I built a simple one back in the 60's from a circuit by FJ Camm using just a 6K7 run from a 6V latern battery for the heater and a B101 67.5V HT battery. With just a pair of high impedance headphones, I could listen to the whole of Europe and if I was lucky, some amateurs an 40 metres as well.

My first mains radio used an ECC83 as leaky grid detector and AF amp with a 6BW6 as output. That used Denco coils and was 'all bands' and gave amazing results on SW. I beefed it up even more with a suggested RF amp using an EF183.

Have a go Marion. There are loads of circuits on the web and you learn a lot by experimenting.

I once built a 7 valver using several designs cobbled together, one from Radio Constructor and some ad-ons from the RSGB handbook. From what I remember, the front-end was from Radio Constructor and the product detector, BFO and Q multiplier were from RSGB. The output stage used an EL91 which I think I cobbled up myself from bits that I had. I remember adding bandspread and an AGC switch, and later an external pre-scaler. It was my pride and joy for several years. A longwire aerial via a tuning unit gave superb results and I spent many Sunday mornings listening to amateurs on 40 and 20 metres. I must have received most of the world on that.

Rich.

Here is your mission, Marion, should you choose to accept it ...!

The colour code on the coil connections are for a Repanco DRR2, should you be able to find one, but Google should turn up a number of ideas for a home-made coil assembly.*

Component values are not critical but some suggestions:

R1 2M2
R2 4k7 (Ideally, an RF Choke should be fitted but a resistor can be used if one isn't available.)

C1 100pF
C2 300 - 500pF Variable Solid dielectric
C3 500pF Variable (One gang of a twin gang unit from a scrap receiver is ideal.)
C4 1n0
C5 2n2

The Reaction control (C2) is usually a solid dielectric type (they used to be cheaper than air spaced) but an air spaced unit can be used. Alternatively, fit a 330 or 470pF fixed cap with a pot - 10k should be ok - in the earthy end.

Using an air spaced Tuning Capacitor (C3) gives smoother tuning. In any case, the solid dielectric types often used in these designs are probably nowhere to be found these days - unless you rob a sub-miniature one from an old far eastern radio!

The value of C4 isn't critical - I've seen everything from 100pF to 2n2 specified here. Similarly, the RF bypass across the headphones - which should be high impedance type - can be anywhere from, say, 1n0 to 4n7.

V1 is whatever you have to hand. Any DF9x type should be OK here and I've seen the pentode section of a DAF9x used.

Of course, you can build a mains operated version if you like but it loses the essential simplicity of the battery version.

* If you wind your own and find that the reaction control doesn't work, reverse the connections to the reaction coil (sometimes known as a 'tickler').

You'd get shot to bits nowadays if you tried some of things in those old books!

Marion

...and therein lies the problem! 'elf an safety' have gone stupid on so many things. When I first got interested in all things electrical, like most kids I built simple things like battery and bulb circuits. One book I had (for 10 year olds) was how to make a battery...not the wussy way from a lemon or an orange but using a glass bottle, some copper wire, aluminium foil and BLEACH as the electrolyte! I seem to remember using a jam jar half filled with bleach and making up two spirals, one of bare copper wire and one of aluminium foil with wires attached, connected to a small torch bulb. It worked but didn't last long as the bleach ate through the foil. The only warning.....Don't inhale the fumes........! Well I knew that anyway and also not to get bleach on my hands or clothes.

There was also another experiment in the book showing how to copper plate a nail using a battery and copper sulphate. That was in the days when you could buy copper sulphate from the local toy shop......!

Rich.

They have ruined all the fun now.
Those chemistry sets were great fun. I can still remember the smell from testing leather to find out if it would burn or not.
The other smelly one was trying to find out what urine would react with.

The other smelly one was trying to find out what urine would react with.

Now then.. I have a feeling you may be taking the........... Oh yes, I think I remember that one

Marion

Spirit radio isn't from Dublin. Carrickroe, Co. Cavan, surrounded on 3 sides by N.I.

I bet you get it better than I.

Go on then, I'll look into cobbling something together - probably after the Christmas period is over.. I like the idea, and can still remember building a triode/pentode audio amp from a design in a book I once had "Teach Yourself Radio Servicing" way back in the early 70's..

I used a a single PCL86 (or maybe it was 82 ) instead of two separate valves.. The output transformer was 'harvested' from a wrecked telly that my granddad kept for spares.. All of the components were similarly harvested..

I built it up one evening, on a chunk of old PCB, diligently selected from a Bush 14" transportable VHF telly (my brother's bedroom set, that he wrecked in a fit of pique when the LOPT went pffzzt-T) and juiced it from a Tri-Ang model railway transformer (for the valve heater supply) and five 12v car batteries for the HT.. I was rewarded with a healthy hum when I touched the input terminal, and decided to give it some input from a BSR SX5H cartridge.. It worked well!

Next step was to find a derelict record player with a good deck.. An old Alba with a BSR UA14 deck came to the call for that.

I can remember the distortion as I wound up the volume, and how much it improved when I increased the HT to 72v, and even better when I gave it the rectified 90v from the UA14's (BSR record deck) motor winding.. I used a silicon diode and a small (ish) electrolytic scavenged from some derelict radio or other.. I had planned to make two such amps, derive my HT via PY82, and build myself a stereo record player.. I guessed at about 3Watts per channel.

Somehow, that never happened, and my little amp just got played around with in various experiments until I got way-laid by other things.. I can recall my granddad calling that amp "Victor".. "Why?" I asked.. "Frankenstein", he said

I would love to get another copy of that book

Does anyone have a copy of "Teach Yourself Radio Servicing"? It has a black and yellow front cover, but I can't for the life of me remember who wrote it.

Marion

I saw it on eBay last night. Have a search.

I saw it on eBay last night. Have a search.

Nice one, Michael..

I'm watching all three

Marion

If you just Google "Teach Yourself Radio Servicing" - including the inverted commas - you'll turn up several more.

The Oxfam shop has the 1974 7th edition (different cover) for £5.99 including postage

http://www.oxfam.org.uk/shop/product/te ... d_97561200

... The circuit Terry put up is just about identical to the first stage in my set bar that I am using a triode valve not a Screen Valve (Pentode) ...

Not surprising, Trevor - it's such a simple circuit that there isn't a lot that can be changed!

One variant that was quite common, as I recall, was to place the grid leak in parallel with the grid coupling capacitor. Sometimes the headphones are replaced by a resistor or a choke and the headphones are connected between the load and chassis via a 100n capacitor. Of course, if you've got a really old set of headphones with exposed terminals, you might prefer this method rather than having live HT right next to your ear!

Using a pentode, instead of taking the screen grid to HT as I've shown, there might be a resistor and decoupling capacitor. One variant is to omit the decoupler and feed the reaction coil from the screen grid, rather than the anode.

The one valver I built over 50 years ago used a pot for reaction but I don't think it was in series with the coil/capacitor as I suggested in my earlier post but I think varied the voltage on the screen grid.

The book I took that original design from was printed as blue prints - white print on dark blue background - with the intention that you should go over the circuit in blue ink as you built it! Even at that young age it occurred to me that it was stupid to destroy the only copy of the design that you'd got and, in any case, it was a library book, so I ignored that particular instruction!

Very interesting, Trevor! What wont be obvious to anybody who hasn't built - or used - a simple one valver, or anything based on the TRF concept, is that, due the variation in Q due to the change in LC ratio across the band, the reaction control usually has to be advanced, or retarded, as one tunes across the band.