"Camms" one Valver

[YT2095UK]

I Finally, after many many years, managed to get all the parts (and time) to build a reasonable copy of F.J. Camms one valver from his 1956 book "A Beginners guide to Radio".
I fired it up this aternoon and you could knocked me over with a feather!
it not only works but WOW! what a sound
it`s crystal clear and picks up better than most radios I have around here (and I have quite a few!).
I had to "Cheat" a little though as I didn`t have a 90v DC battery supply nor indeed any 90v supply, only my 280V one that you can just see in the background of one of the pics.
so I used a 100k resistor feed to the anode, and took the audio through the HF choke and phones and then down to deck.
it`s only a Minor alteration however and I`m sure it can`t be held against me
the rest is layed out as close as possible to the original drawings too.

the headphones are ex-soviet military and 3200 ohms, a number 76 valve, a multi cellular HF choke (circa 1929), a pair of hank wound coils I made and some second-hand air capacitors. and Yes, the control knobs on the front are Cossor Melody Maker ones

I`v included a few pictures:

[kalee20]

Well done! FJC's spirit lives on!

[Dave Moll]

Originally Posted by YT2095UK

I didn`t have a 90v DC battery supply nor indeed any 90v supply

There's always the standard option of 10 PP3s connected in series.

[Sideband]

This looks very similar to a radio that I built when I was about 12. I remember winding two coils just like that and you move them around for best reception just before oscillation. You may well have the same book I borrowed countless times from the local library. I think the original circuit used a 1T4 or DF91. Wonderful when you can cobble bits together like this and come up with a good working radio. That's what made the hobby so facinating for me. I found getting a simple basic radio like this to work well is more satisfying than building a good superhet because you know that the superhet will probably work reasonably well from the start.


Well done. Now you've really got the 'bug' what is next on your list?


Rich.

[YT2095UK]

well, next I`m planning on trying the same thing out again but using a Pentode instead of a triode, as I want to see what will happen if I put in a signal to the screen grid from a sig gen while the Control grid is hooked up to an untuned antenna, I`m hoping that there will be phase cancelation that will strip the carrier and leave me with just the audio part of a radio signal.
but I`m not going to be doing this until I`v experimented fully with different coils in this set and made plenty of notes on them, then when I get a nice working set of them, it would be nice to have a band selector switch on it.
I`v already made a coil that will take me down past 60KHz (VLF listening is another hobby of mine), then of course I`ll want to amp it up so that I`m not restricted to earphones and Others can listen to it at the same time.

it`s interesting to note that the rxn coil has to increse in windings along with the tuning coil, and that just changing the tuning coil alone leads to limited or Over rxn depending on witch way you go (up or down in frequency), I find that the Higher the frequency, the less rxn is needed, and the lower you go full rxn is sometimes not enough and more windings are needed.
something to bear in mind when I make a band selector!

[paulsherwin]

Do you have a scan of the original article which you could attach to the thread? it would be interesting to look at it and compare it with your fine efforts.

You might want to try a few different valves and see how they function if you have any to hand. I'd expect most small signal triodes and pentodes to work - 6K7, KTW63, EF36, EF37, EF39, EBC33, lots more - and that's just the octal ones

Paul

[YT2095UK]

here`s the Book itself in PDF format (if it uploaded ok), I find it easier to use this rather than the book itself in the workshop, I don`t want it getting mucky and blowing up and printing certain key parts is handy

Enjoy!

I Do have a few different triodes, but they`re all as doubles, the ECC sort and EABC as well as some that don`t have numbers anymore? I`d love to have more single triodes, but the #76 was all I could aford, and I must say, that even though it only has a gain of 10, it works remakably well

oops, a problem
"Your submission could not be processed because a security token was missing or mismatched.

If this occurred unexpectedly, please inform the administrator and describe the action you performed before you received this error."
when trying to UL the PDF (it`s only a 794k file too?)

[MichaelR]

This site has some very useful downloadable material including the Camm book.

http://www.portabletubes.co.uk/sitefiles/downloads.htm


Ok to copy by the way as all of the material for one reason or another has passed out of copyright jurisdiction.

Mike

[YT2095UK]

after spending quiet a bit of time trying to get this sorted and with Pauls help too, it seems the problem is My end, the file that said about 900k on THIS machine, says 23MB on the others!
no wonder all my email clients laughed at me
anyway, I`v installed an FTP program and managed to UL it to my website (after knocking all the dust off it).

the book can be Downloaded here: http://myweb.tiscali.co.uk/yt2095/ra...dio%201956.pdf

Be Warned however, this is a large file and may take a minute or 2 to load up!
and you`ll need Abode PDF reader as well.

[See post #12 for a smaller version - Moderator]

[Herald1360]

Originally Posted by YT2095UK

well, next I`m planning on trying the same thing out again but using a Pentode instead of a triode, as I want to see what will happen if I put in a signal to the screen grid from a sig gen while the Control grid is hooked up to an untuned antenna, I`m hoping that there will be phase cancelation that will strip the carrier and leave me with just the audio part of a radio signal.

That sounds suspiciously like a homodyne, or a variant thereof.....

http://www.thevalvepage.com/radtech/synchro/synchro.htm

Chris

[YT2095UK]

it does indeed look very much similar to my idea! I know it works with CMOS chips as I`v done this before with basic logic gates whereby if this and this (antenna signal and sig-gen frequency) are the same then 0, anything else can pass.
I also remember Decades ago when my mate/Mentor used a small RF generator next to his SW radio to make some signals come through cleaner.
it seems my assumption of the same thing using 2 of a pentodes grids would work also.
I don`t mind re-inventing the wheel either, it just means I`m on the right track

[paulsherwin]

I have extracted and uploaded the relevant part of the Camm book. It is now a more reasonable 1.9MB but it isn't as readable as the original because of multiple recoding and compression. It's OK as a quick reference though.

Paul

[YT2095UK]

That`s Fantastic! thanks Paul

BTW, I took your idea about using Other triodes, and decided to retrofit it with an Octal socket as well, wired pin for pin to the existing one, so that any changes to the Original automatically effect the other.
it may even be an idea to fit a Heater switch between the two just for safety.

here`s what it looks like now.

[Ed_Dinning]

Hi YT, if you are looking for novel detection methods google Synchrodyne. It was a great desig by prof Tucker at Birmingham many years ago, written up in Electronic Engineering in the late 40's early 50's.
Coupled to a Mullard 3-3 it makes AM sound great.

Ed

[YT2095UK]

Originally Posted by paulsherwin

I'd expect most small signal triodes and pentodes to work

as would I, but now I`m Totally flumoxed by something, the 12AT/BH7`s work (ECC81/82`s) but the ECC83 doesn`t want to know!
I`v tried several and they were all (not to put too fine a point on it) Crap!
no regen whatsoever and very "dim" sounding.
I would have Thought that Logically, having a mu of ~100 as opposed to about 10 would have forced me to back the rxn off, but instead there`s hardly a thing come out of it at all, Almost as if I had the rxn coil backwards.

I refuse to beleive that my 83`s are down as I tried 3 different ones, 2 of which are from Currently working circuits.

the anode is fed by a 150k resistor (the 100k was getting hot long before I did this retrofit), I`ll try biasing the cathode for it in the morning and using different grid dropping values.
I really expected the rxn to have gone insane with an 83, this has got me puzzeled now

Ed, I shall do that when I get a quiet 5 mins (probably in the morning with a coffee), I have the other site bookmarked too, so all being well it should be a Great day tommorow

[paulsherwin]

I'd expect an ECC83 to work, but they were designed for audio use so maybe the internal capacitance is too high. I'm surprised though.

Paul

[YT2095UK]

me too, esp since I`m only listening to 47KHz which is only a tiny tiny bit above audio, and that I use an ecc83 in a modified Bush FM front end box instead of the 85.
I would have laid wager on it working, and possibly even Too Well.

my wiring has to be right also as the 81/82`s wouldn`t work either and they`re pin-for-pin compatible, Hallow`en Gremlins anyone?

[OErjan_S]

uhm, check the bias on the grid, it may be out of desired area as this is a selfbiasing thing (grid leak), sometimes I have had to go as high as 18Mohm to get correct bias, others as low as 220k.
also try to use only 27V or so on the plate, perhaps as low as 18v.

[YT2095UK]

I`m not sure what`s on the plate to be honest, I never checked, but I know it`s less than 90V as it won`t fire up an NE2 bulb (I used it for a simple voltage reg, but found I didn`t need it).
I used 4.4M Ohm (even shown in the latest pic) but found that at Higher freq`s a 1M Ohm will be just fine too (typically radio 4).
there is no real cathode bias for this set-up, as shown in the cct diag PDF that Paul did, it`s hard to deck and working fine.. well except for the 83`s that is. *sigh*

[Sideband]

Originally Posted by paulsherwin

I have extracted and uploaded the relevant part of the Camm book.

That's it! Exactly the same book I borrowed some 40 years ago from the local library. You were only allowed two weeks but that was not long enough to go through the book properly so I kept extending the loan and had it for over a year eventually.

I remember playing with that exact same circuit. I used a 6Q7 (EBC33) instead of a directly heated triode. It worked brilliantly as did all the other circuits Camm described. Happy days!