Quote:I'm not near any relavent information at the moment, but experiments with twin triodes designed for cascode amplifier use do seem a little reluctant to oscillate, on one occasion particularly in my case because I tried to use the section in a type that has its internal screen connected to its grid! I don't suppose you have done anything that silly ![[Image: rolleyes.png]](https://golbornevintageradio.co.uk/forum/images/smilies/rolleyes.png)
One aside that worked surprisingly well, was while investigating superregenerator circuits, that they don't take a lot of modification to produce an acceptable self oscillating mixer for a low IF pulse counting FM receiver ...
The home brew IF transformer experiments I will claim as a resounding success, however trying the same shortcut to make a local oscillator for a superhet has proved difficult as the available range of values don't coincide with anything that will allow decent tracking... We can't have it all though.
Glad your IF experiments are successful.
After reading your post, I have checked in case I was a muppet. The internal grid pin 9 for ECC85 is grounded. The Hartley oscillator is very simple and I checked many times for silly mistakes. I never had any issue with oscillators using pentagrid values for MW. With FM, thing starts to get difficult and unforgiving for wirings and components layout. I tested the nuvistor pre-amp and mixer, they are all working. When i probe the anode resistor of the ECC85, it starts to oscillate strongly!!! I cannot find a logical explanation for it. I use a cheap TinySA spectrum analyzer with its antenna to check oscillation frequency and strength. Any scope probing would load down and detune the oscillator at VHF frequency. Once I get the oscillator working, it will be all fine.
I keep thinking about the shorten quater wave transmission line used in the oscillator of the Leak Trough Line:
http://www.adventuresinhifiaudio.com/18/...er-design/
I wonder i can make a FM oscillator rig with a coaxial copper pipe as 1/4 transmission line.
I built a one valve 6C4 (half 12au7) superregenative FM receiver last year, it worked ok. I have not explored low pulse counting FM yet.
regenfreak Wrote:I keep thinking about the shorten quater wave transmission line used in the oscillator of the Leak Trough Line:
http://www.adventuresinhifiaudio.com/18/...er-design/
I wonder i can make a FM oscillator rig with a coaxial copper pipe as 1/4 transmission line.
A year or so ago I did have some success with a vhf circuit, (again an FM band superregen that used a twin triode for detector + AF amp that used a transmission line for tuning that I called a trombone tuner*. It was a U shape piece of heavy tinned wire, (think 100 amp fuse wire that had a coil incorporated on one end that was loading for the top end of the FM band), it was tuned by pulley and cord system that pulled a sliding contact along between the parallel section of wire. I have the notes and dimensions for that with the actual device, unfortunately not here! (In a biscuit tin two counties away!) The only real problem with that was having the connections to the valve from the tuned circuit short enough... That performed best with the detector changed to a UHF triode.
More by luck than judgment the bandwidth of that tuned circuit was just right, and reasonably noise free slope detection was possible, and although a simple self quenched design, its quench ran at about 30 kHz and the audio is acceptably entertainment quality: listening to music with it, is a pleasant enough experience.
*The project was encouraged by "Kalee20" (Peter) and "reset" (Greg).
Hi Folks, why not go to the PCC84 as used in TV, it was a good reliable valve and seems to have had less problems than the ECC85, which got a bit of a bad name.
You could also go further and look at the UHF tuner valves PC86/88/97/900. Slightly odd heater voltages and only single valves but most electrodes are double pinned on the base for low inductance.
Also plenty around and really cheap
Ed
Quote:A year or so ago I did have some success with a vhf circuit, (again an FM band superregen that used a twin triode for detector + AF amp that used a transmission line for tuning that I called a trombone tuner*. It was a U shape piece of heavy tinned wire, (think 100 amp fuse wire that had a coil incorporated on one end that was loading for the top end of the FM band), it was tuned by pulley and cord system that pulled a sliding contact along between the parallel section of wire. I have the notes and dimensions for that with the actual device, unfortunately not here! (In a biscuit tin two counties away!) The only real problem with that was having the connections to the valve from the tuned circuit short enough... That performed best with the detector changed to a UHF triode.
Brilliant
Very impressive. You live following the true spirit of a radio experimenter. Your set-up reminds me his rig of measuring air variable capacitor loss using copper pipe transmission line:
http://g3rbj.co.uk/wp-content/uploads/20...ssue-3.pdf
Certainly it would be much cheaper than building VHF cavity or helical resonator. Copper pipe of large diameter is expensive.
Quote:ore by luck than judgment the bandwidth of that tuned circuit was just right, and reasonably noise free slope detection was possible, and although a simple self quenched design, its quench ran at about 30 kHz and the audio is acceptably entertainment quality: listening to music with it, is a pleasant enough experience.
The squeal of 6C4 superregenative receiver hurts my ear. It was a simple weekend project. The theory behind ithe superregenative receiver fried my brain.
Quote:Hi Folks, why not go to the PCC84 as used in TV, it was a good reliable valve and seems to have had less problems than the ECC85, which got a bit of a bad name.
You could also go further and look at the UHF tuner valves PC86/88/97/900. Slightly odd heater voltages and only single valves but most electrodes are double pinned on the base for low inductance.
Also plenty around and really cheap
Ed i might try. I also have a pair of new 12DT8 (like 12AT7 but with screen between triodes) which i can try in my oscillator test rig..
(03-05-2021, 06:12 PM)Ed_Dinning Wrote: [ -> ]Hi Folks, why not go to the PCC84 as used in TV, it was a good reliable valve and seems to have had less problems than the ECC85, which got a bit of a bad name.
You could also go further and look at the UHF tuner valves PC86/88/97/900. Slightly odd heater voltages and only single valves but most electrodes are double pinned on the base for low inductance.
Also plenty around and really cheap
Ed
Hi Dr Ed.
I think the Brimar 7AT7 that I have a couple of new examples is an equivalent of the PCC84, good valve and little interest from the tube rollers. One of the more successful superregen circuits I tried used an PCF80 and PC97, pentode section of the 80 for RF amp/aerial isolation, 97 for SRA, triode section of the 80 for AF ... May seem odd but took a step away from instability caused by using multiple section valves for the SRA.
One of the things I found that I had to get my head round was that the superregen self quenching circuit is an amplifier that efectivley produces a pulse position modulated output: including a tailor made AF stage that discriminates that signal makes for a much more successful AF receiver...
Hi Amie, nice discovery on the quenching of a superregen.
Something stirs in the old brain that an article was written on it somewhere in the past, weather a practical circuit or just theory I don't remember
Cheers, Ed
A super-regen - especially on FM - is probably the most extreme example of a simple circuit that's hardest to analyse.
Triode, tuning capacitor, tapped cathode coil, grid R, grid C, anode R, anode C, DC blocking cap - and you can get AF output from 8 components, and at entertainment quality, just as Amie claims
and whose work inspired me just over a year ago.
But the maths is appalling!
There have been some good papers on the subject over the years, I don't have the links to hand here but Marcus Scroggie was published on the subject in the 1940's in Wireless World, (doesn't reference Armstrong's work), there's a paper by Prof. Eddie Insam of Bristol university that's very good, and for some real night time reading a post graduate paper from an MIT team, who I will not insult by attempting to spell their names without checking first.....