There was just a link to a 12AX7 radio. Let's see if we can find it.
EDIT: Nope, it was 12AT7. But here it is anyway.
http://cool386.tripod.com/12at7/12at7.html
EDIT: Nope, it was 12AT7. But here it is anyway.
http://cool386.tripod.com/12at7/12at7.html
It might be possible to build an AM radio with a 12AX7, but its performance would be very poor. You would need a long wire antenna to get any kind of reception and selectivity is not good.
The single "bottle" FM circuit Pano linked is quite sophisticated and will do nicely on strong stations. For table radio use, a power amp in addition is necessary. The power amp could be built from a 'X7 and a 6L6.
The single "bottle" FM circuit Pano linked is quite sophisticated and will do nicely on strong stations. For table radio use, a power amp in addition is necessary. The power amp could be built from a 'X7 and a 6L6.
Very cool FM super regen, think I might want to build something based on this design..
Technically, it's an AM setup used to slope detect FM. It is not immune to AM noise, but it is signal seeking.
The use of a single 'T7 section as both a grounded grid RF amp and a reflex common cathode AF amp is elegant. That triode isolates the oscillating detector from the antenna, provides some RF gain, and provides a fair amount of AF gain.
Need more information. What kind of radio? (TRF? Regen? Superhet?) What frequencies did you have in mind? (ELF, VLF, LF, MF, HF, VHF, UHF+) What are you intending to receive? (AM, SSB, FM, digital?) Depending on what you have in mind, may be going solid state might be the better solution?
It all depends.
True, and in my case it would be only used for strong local signal reception since I live very close to downtown Boston.
I've made some regens for AM reception, and audio quality is pretty fine IF PROPERLY OPERATED. It takes a few time to get the received adjusted, but when you get familiarized, it works very good.
But, for a good regen, you need the lower mu triode you can get, and the lower +B compatible with the audio output, so a little of practice, you will get a good compromise. Remark that lower mu is important, medium or high mu triodes or pentodes make exact regeneration point difficult to find.
But, for a good regen, you need the lower mu triode you can get, and the lower +B compatible with the audio output, so a little of practice, you will get a good compromise. Remark that lower mu is important, medium or high mu triodes or pentodes make exact regeneration point difficult to find.
Be careful of superregens, unless you have no near neighbours. Even with an RF amp they can still radiate mush. They are also not known for low-distortion audio, as they have an exponential response.
Those with no previous radio experience could start with a regen (not superregen), perhaps combined with reflex. Then try a simple AM superhet. Leave VHF FM until last, unless you enjoy disappointment. RF is harder to get right than audio, because all the parasitic components which never appear in the circuit diagram have a habit of biting you when you are not looking!
Those with no previous radio experience could start with a regen (not superregen), perhaps combined with reflex. Then try a simple AM superhet. Leave VHF FM until last, unless you enjoy disappointment. RF is harder to get right than audio, because all the parasitic components which never appear in the circuit diagram have a habit of biting you when you are not looking!
Very cool FM super regen, think I might want to build something based on this design..
I did but couldn't make it work without some annoying noise. Of course you know a lot more than I do so don't give up just yet.
Boy, don't care. I´m manipulating RF since 1985 when I was 15, when I made my own 6DQ6 AM 30W emitter, and the receiver. The TX has the power trafo and modulator choke winding of my own in an old manual drill used as a winding machine, and counting turns manually.
Regens receivers, when properly constructed and adjusted DO HAS BETTER AUDIO QUALITY because YOU fix at any moment RF bandwidth and haven't converter, IF and detector distortions. As a regen fan, I can sure this fact. And, there is a difference in supper-regens, and regens. Regens doesn't need to oscillate, but in some circumstances, is need it does it (For example, when receiving CW or SSB). Super regens always oscillate, and the quenching oscillation is capable of cause QRM to other receivers.
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Regens suffer from the problem that gain and bandwidth are linked via the regeneration control. In Europe at night it is quite likely that the next audible station is only 9kHz away. The leaky grid detector can be something of a compromise, although no worse than many diode detectors. No AGC to counteract night fading. A superhet can provide better audio, although most do not because of too narrow IF bandwidth and diode detector loading.
They don't have to. The design goal is usually communications effectiveness, not fidelity. For SSB, fidelity is impossible, and for AM, not legal, as the BW is quite limited, even for commercial. BCB AM. Thus, the "too narrow" IF filters -- too narrow for fidelity, but not for what they were designed for.
You have to watch out for that in audio design as well. Especially when using pents or cascodes. Don't keep the strays under control, and it'll probably oscillate.
For those interested in Regens, there is a forum regenrx at yahoo groups. I´m registered there. Yesterday I was testing my RegenFET and found an interesting device called 2SK427 that has a curves family much similar to triodes, and as a regen works very fine. I did a cascode previous to it with a 2SK117 (down) and 2SK246 (Upper) and get about 400mV at the audio output from a ferrite antenna coli. This is the receiver for my RegenFET (an all-FET no BJT no IC) MW regenerative portable AM receiver. Briefly I post a schematic for those who want to play with it.
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