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Old 9th Dec 2009, 8:55 pm   #21
kalee20
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Default Re: My new Superheterodyne!

If you add AGC (you already have the circuitry back to the IF valve) you'll want to change the EF91 for an EF92. The EF91 isn't variable- so changes in bias won't have much effect on gain.

Also, if you add a tuning indicator, you can have a lot of fun with it! Especially if you have delayed AGC, you can try the operation from the AGC line (when it probably won't deflect for weak stations) and from the demodulator (when it will).

Incidentally, I like the reasoning behind the volume control connection. The same's occurred to me, though as I've always had the control on an earlier stage with a resistive anode load so if the wiper does ever lose contact, there's no danger of the valve frying.
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Old 9th Dec 2009, 10:06 pm   #22
YT2095UK
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Default Re: My new Superheterodyne!

funny you should mention that, Herald sent me a couple of EF92s a week or so ago, and I tried one based upon the idea that seemed a shame to use 91 that will do VHF, when a 92 that that will do HF for a LW/MW radio.
and although I can`t exactly say it didn`t work, it was Incredibly Quiet in comparison and required Full volume to be listenable, and that came with the requisite Hum that full vol will give (esp when your shielding is as bare as mine).
it would be Nice to have it compatible with both, but I don`t think the cct is "Stiff" enough yet to support both.
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Old 10th Dec 2009, 3:02 pm   #23
Neil Breward
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Smile Re: My new Superheterodyne!

Hi - Odd that the EF92 was so poor, maybe it was a dud? Anyway, I'd leave the EF91 there for now, it does have a greater gm than the EF92. The AGC will work with an EF91, but it will be a bit fierce as this valve has a sharp cut-off. Better to connect your ECH81 grid via a 1 Meg resistor to the grid feed resistor and decoupler cap so that you've got a little more control over the overall gain.

I like this valve line-up! I don't remember seeing this combination in a commercial set but there's nothing wrong with that ...

Cheers,
Neil
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Old 10th Dec 2009, 7:46 pm   #24
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Default Re: My new Superheterodyne!

Thanks for that!
the valve line-up was largely dictated by what I had in many boxes of assorted valves, I`v been going through them over the last few months putting them into some sort of order.
I`v only been here a short period of time, and joined only having a basic idea of what a Triode was, seriously!
I new nothing of how I.F worked or what it did either, but thanks to the patience of the guys here answering many of my Numerous questions and putting me right when I was wrong, the technology was elucidated, and then applied/Built

the really cool part with this valve line-up is that I have at least 5 replacements for any one valve with the exception of the EBC90 (I only have 2 of them), so this radio should last for quite some time, AND also provides a working template on which Other radios can be made, and yes I have plenty of small double diodes and triodes if the EBC90 ever failed.

it`s also a nice way to use up what others may consider Scrap.
and that brings me nicely to my next point that, after much consideration, I`v decided to call this radio the "Womble One"!
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Old 11th Dec 2009, 10:47 am   #25
Neil Purling
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Default Re: My new Superheterodyne!

What's the power supply arrangements?
One of those sketches isn't coming up, but I think it is the second IF.
It's a wonderful effort. I ought to get off my backside and do one too, instead of TRF's.
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Old 11th Dec 2009, 12:37 pm   #26
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Default Re: My new Superheterodyne!

the PSU is one I also made out of spares, it`s a Cossor transformer, some electolytics out of an old Scope chassis that was given to me some 15 years ago, an GZ34 rectifier I found in my rectifier box, and some power resistors that I bought.
I get my 6.3VAC and about 250v under load, I use a 7W pygmy buld when I`m prototyping as balast to limit the current and show any fault conditions.
here`s some pics:

https://www.vintage-radio.net/forum/...2&d=1257960301
https://www.vintage-radio.net/forum/...1&d=1257960301
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Old 11th Dec 2009, 8:36 pm   #27
Neil Purling
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Default Re: My new Superheterodyne!

I checked my valve box & found two 6K8 frequency changers and several new 6K7's.
I suspect the little beggars have been quietly reproducing. There's even a used 6Q7G and a EBC33, which is actually marked AR21. I thought about using something somewhat unusual/perverse for the o/p or do you think I should use a plain old 6V6?
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Old 11th Dec 2009, 9:04 pm   #28
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Default Re: My new Superheterodyne!

well, I based my choice on a few things, How many of each type of valve needed do I have?
Do I have/can I get the valve holders for these?
which out of my shortlist are the best for each job I want it to do?
and that`s about it really, I had my valve line-up
others may do it differently and just consider which are the best valves for the job that they have, and then use those.
as for the Audio, go with whatever works the best for your needs, for me the el84 was just right, and it would have been a waste to use something that would push 20 Watts when it`s only ever going to see a 3W speaker.
having said that I have built a general bench amp using an 807 that spends most of it`s time pushing about 2 Watts, but in my defence the idea was that it would last much longer being under-driven, and the extra power is always there if I need to test something. but for a home radio anything between 1 and 5W is just right (and I`m more than half deaf).
if you really wanted Perverse try using a load of ECC81/82s in parallel, or a PL36
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Old 11th Dec 2009, 10:06 pm   #29
Neil Purling
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Default Re: My new Superheterodyne!

Auction Gods willing there's a Pye P116U Piper that is gonna be mine. Keep off please!!
If it runs' fine. If not, it doesn't matter, because it is for the chop.
That would provide all wound components, frame aerials, variable capacitor, a switchpot & a speaker.
The only trimmers I see for the mixer & osc are probably on the variable capacitor.
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Old 11th Dec 2009, 10:13 pm   #30
YT2095UK
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Default Re: My new Superheterodyne!

Hmmm... I`m not sure I could do that unless it was a complete nail, how about asking on here for anyone with some scrap chassis they don`t want and build something out of those?
seems a pity to take something appart that can be fixed.
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Old 11th Dec 2009, 11:46 pm   #31
Neil Purling
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Default Re: My new Superheterodyne!

Unless you have a 45A/15A chassis I can re-work or rob one of parts...........
I chose that which I thought would not be a loss if it was filleted. The Pye Piper is hardly a shining example of a quality radio.
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Old 11th Dec 2009, 11:53 pm   #32
Sideband
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Default Re: My new Superheterodyne!

'YT' I think you've started something here! It's about 30 years since I last built a radio and that was a 7 valve superhet covering MW and SW with a BFO and a Q multiplier built in. It was actually a combination of two published designs with some extras from the RSGB handbook.

Some time ago I came across a radio design using TV valves with push-pull ECL80's in the output stage. I think I might while away some cold winter evenings by getting something going. I suppose it's not the same as starting from scratch and designing your own and I have done that in the past. 40 years in the trade and I'm quite happy to build something that at least has a fair chance of working and then 'tweak' it to suit.

The idea of using some TV valves for a radio is sufficiently 'quirky' to be interesting.


Rich.
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Old 16th Dec 2009, 2:25 pm   #33
Neil Breward
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Default Re: My new Superheterodyne!

Quote:
Originally Posted by Richard_Newman View Post
'
Some time ago I came across a radio design using TV valves with push-pull ECL80's in the output stage. I think I might while away some cold winter evenings by getting something going. I suppose it's not the same as starting from scratch and designing your own and I have done that in the past. 40 years in the trade and I'm quite happy to build something that at least has a fair chance of working and then 'tweak' it to suit.

The idea of using some TV valves for a radio is sufficiently 'quirky' to be interesting.

Rich.
See my design in the Summer(?) 2006 copy of The Radiophile for a quirky set using TV valves - and a twin-ECL8O push-pull output . . . and yes, it works very well !

Cheers,
Neil
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Old 17th Dec 2009, 4:49 pm   #34
dr peppers
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Default Re: My new Superheterodyne!

Excellent, I like your PCB!, and the seperate tuner head, did you not have a piece big enough.
There wont be so many of those around, I've never built a radio with valves, I did have a go at making a plasma tweeter a while back but it sounded naff.
The EL84 should certainly make enough noise.
I build stuff all the time, all kinds of stuff and its good to see someone else doing it, people like us are fading out and becoming 'weird', nintendo has taken over.
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Old 17th Dec 2009, 6:48 pm   #35
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Default Re: My new Superheterodyne!

Thanks!
actually if you follow the "saga" beginning to end and all the threads leading up to this point (I knew Nothing of I.F stuff), I wanted to build this all as a Modular system, with one section per function.
the reason being that is that it would allow me to prototype a section and check if it works by hooking it up to my Existing sections.
rather than build it all as One unit and find out later that I need more room or have to alter something serious.
the amp was nothing to consider, the demodulator had to built and tested them commited to that board along with the IF preamp, that way Both Unknown cans were used so that I could test them, I guessed at the order they went in and it turns out I was right 1`st time, Red 1`st and then the Yellow, AND it worked on the RF gen by passing the modulated tone at One frequency only.
I had enough room left on the card to make an amp, so I did.
I would love to have more of that card/board material but don`t know where to get more?
that left the Tuner part, that was the scary bit for me as I knew even Less about them than I.F stages
but after several questions and studying of all the cct diags I could get my hands on, I boiled them all down to a General idea, and then set about employing it using the bits that I had.
after a bit of faffing (I forgot to earth a whole section!) that took all morning, I finally got it working!
and with a plain old 2 pole switch instead of these 4 pole ganged wave changers.

but Now, after my latest hack, I`m likely to be the 1`st guy to own a valve radio with digital frequency readout as well.
anyway, I Like "Weird"
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Old 2nd Jan 2010, 11:34 pm   #36
Lloyd 1985
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Default Re: My new Superheterodyne!

Hi
your thread on building this radio has inspired me to have a go! I've used most of your design, but I've changed a couple of things. I didn't have an EBC90, so after a quick bit of research and a dig through the valve pile, I found an EBC81 should do the same job! I also bought a box of radio bits, and got some IF cans, the aerial and oscillator coils from a cossor (possibly a 520) and the wavechange switch! since I had all those bits, I've decided to copy the circuit of a cossor 520's mixer/oscillator and add it to your diagrams. no idea if its going to work yet!! I did have the amp, detector and IF amp working, I was getting the test tone on 465kc/s! This is the first time I've actually tried to build a valve radio, so there's a lot to learn so far I'm quite enjoying it. when I get a bit further on with it, I'll start a thread about it.

thanks for this thread!
regards,
Lloyd.
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