hi i find that a good trf set seems to pull in stations better than the superhets i have, they don't tune as sharp but they will pull in stations with more vol.. ihave a majestic 132 trf which outperforms most of my superhets.one thing though is i live in an area with few stations so the am band is not crowded maybe its my imagination but i don't think so. butch
At any rate, with the exception of the local oscillator and that the various stages of RF amplification are fixed instead of tunable, the superheterodyne radio is not at all different in any way than the TRF receiver. The more stages of RF amplification using tuned transformers, whether these be fixed in the case of a superhet, or tunable in the case of a TRF, the more selective the radio is and the more sensitive it is. Since mechanical parts are extremely difficult to engineer to synchronize at all times, the superheterodyne will often outperform a TRF simply because since the IF transformers are never adjusted while tuning in stations, they may be adjusted very closely for one frequency and always be sensitive. If the oscillator does not track perfectly with the antenna circuit, this will not decrease volume, but will simply shift stations around just a bit, so synchronization of the condensers is not as critical. Many TRF receivers used triodes, which are not very strong amplifiers. Most superheterodynes use screen grid tubes. Many of the four tube TRF receivers, i.e. 24A, 24A, 47, 80, don't even have a primary audio amplifier, though at least the RF tubes are tetrodes (screen grid tubes). These sets cannot be expected to outperform a superheterodyne. Many designs lack an automatic volume control circuit, which greatly aids in sensitivity. I would expect a properly tuned TRF, with 3 or 4 screen grid RF tubes to perform as well as a superheterodyne with 3 or 4 RF tubes. I don't think it would perform much better. Perhaps. Anything is possible with the right parts and design. One must remember that the converter also serves as a sort of RF amplifier tube in the mixer section of a superhet.
Honestly, though, I do not remember ever saying that TRF receivers outperform superheterodynes. Many times they don't. With a long tunnel of RF circuits to travel through, they can be quite selective and sensitive with all that amplification. The small 4 and 5 tube sets, especially if they utilize triodes, are not likely to outperform a superheterodyne. The thing I usually mention about TRF receivers is their superior fidelity, partially owing itself to a TRF's inability to stay perfectly synchronized. By being ever so slightly out of sync., a broader band of audio may be passed through. There are other reasons for this higher fidelity, too, such as the lack of an oscillator, so there aren't as many noises such as the harmonic notes you get when beating two frequencies together. Since they are not present, tone filtering does not have to be as severe. There's a whole lot to why they have slightly superior fidelity that I can't remember right now, but I'm sure that others in here can hit a few points. I'll have to do some reading. Also it should be remembered that many manufacturers like Grunow and Philco put out expandable IF bandwidth high fidelity superheterodyne sets. The expanded bandwidth passed as much as 10KC, which is quite fine for listening pleasure, but of course this ruined some selectivity, allowing strong local stations to overlap. That said, though, some superheterodyne AM radios are capable of the fidelity of a TRF. Of course FM radios are superheterodynes, too, but when FM was designed, they took advantage of every high fidelity feature they could and designated stations far enough apart that a wider bandwidth could be used. When AM came out originally, they crowded all the stations together in 10KC incraments.
Anyway, by reading the above and realizing that a superheterodyne is no different in basic principle than a TRF, except that it uses a local oscillator to create one constant frequency so that the RF stages may be fine tuned to that one frequency, it will be understood that whether the radio be a TRF or superhet, the more stages of RF amplification, the more sensitivity and selectivity. The only real difference between the two for performance is fidelity. The superheterodyne is favorable for an inexpensive receiver because it affords much sensitivity and selectivity with fewer parts by eliminating condenser gangs and RF coils, and perhaps by eliminating a stage of RF amplificiaton because the remaining stages are tuned so well. Since it works so well for the inexpensive receiver, it is also desirable for the more expensive receiver, as here, too, the cost and parts count may be kept down to some extent.
Thomas
:::Thomas Dermoody made several interesting observations concerning sensitivity/selectivity issues a few weeks past. Based on my education, experience and theory, a super het should outperform a TRF hands down. I have recently restored an Edison 7R and a Majestic 90B, both TRFs. In both cases, I have peaked the trimmer caps (the sole adjustments) across the ganged tuning caps on both ends of the dial. I have also restored a Philco 48-460 6 tube super het, with a pristine BAKELITE case. My shop has a concentrically wound (approx 1 1/4 turns) #20AWG antenna at the ceiling, creating a quad approximating 15' x 20' for the TRFs only. In several instances, I've read glowing comments from Thomas about the projected performance of many old restored TRFs. In my case, the super het with its small internal case antenna, setting on the workbench, consistently outperforms the TRFs, DAY or NIGHT. Thomas, are MY OBSERVATIONS unsubstantiated?
:
:hi i find that a good trf set seems to pull in stations better than the superhets i have, they don't tune as sharp but they will pull in stations with more vol.. ihave a majestic 132 trf which outperforms most of my superhets.one thing though is i live in an area with few stations so the am band is not crowded maybe its my imagination but i don't think so. butch
:Thomas
:Thank you for the very timely response. I didn't quote you directly as saying TRFs are better than superhets, only that you had made glowing comments about the projected (probable) performance of various TRFs, when properly restored. In comparison to what? Sorry for the misinterpretation. My observations have concluded that the superhet is both more sensitive and selective. I'm only trying to establish whether I have restored these TRFs to their full potential. My resources are limited as are my test equipments (analog VOM, DMM, restored tube tester, restored condenser tester) My superhet has no RF amp stage, but a dual ganged tuning condenser would indicate at least an antenna tuning circuit ahead of the hetrodyne converter and an oscillator tuning circuit, whereas the TRFs, (both essentially the same circuit) have a 6 gang condenser for both RF input and output tuning of 3 amplifier stages. The superhet converter(mixer) does possess gain (apparent gain) using the preferred high side injection of the local oscillator. The resultant IF waveform is always greater in amplitude (millivolts) than the RF (microvolts). The natural bandwidth limiting of properly designed IF stages greatly enhances not only the selectivity, but sensitivity as well. I guess in the Heydays of early AM radio, any radio that would tune a station or two was a modern marvel of compelling magical powers, and what is this selectivity, sensitivity thingy anyway. Nostalgia Air's presence on the web and at my finger tips has greatly enhanced my sensitivity and selectivity this year. Happy Holidays to you Thomas, and Norm, and to ALL the learned Cadre at Nostalgia Air.
::Here's the trick, folks: The way a superheterodyne radio works is that the stages of RF amplification are all tuned to one frequency, and this never changes. A local oscillator beats a predetermined frequency with the incoming frequency to make the required Intermediate Frequency, which is tunable by the following stages of RF amplification (the IF amplifiers). Some radios have an RF preamplifier. Some of these radios have this stage tunable with an extra gang on the condenser so that it synchronizes to the antenna frequency. In this case the RF preamplifier is exactly the same as any stage in a TRF receiver. Some receivers have this stage left wide open with no tuning capabilities what-so-ever, so that it will pass all frequencies tunable by that particular radio. This cuts expense by eliminating another gang to the condenser, and often this stage of broad band preamplification will be resistance/condenser coupled, thus eliminating another expensive coil or two. This stage usually has a wave trap, though, seeing as since it is a broad band amplifier, it will easily pass the IF frequency (commonly 455KC). The wave trap is often tuned to this frequency. Since the IF transformers down the line are tuned so well, and cannot go out of sync. because they are not adjusted during the normal tuning procedure, this broad band preamplifier works well. The IF stages later will afford enough selectivity on their own.
::
::At any rate, with the exception of the local oscillator and that the various stages of RF amplification are fixed instead of tunable, the superheterodyne radio is not at all different in any way than the TRF receiver. The more stages of RF amplification using tuned transformers, whether these be fixed in the case of a superhet, or tunable in the case of a TRF, the more selective the radio is and the more sensitive it is. Since mechanical parts are extremely difficult to engineer to synchronize at all times, the superheterodyne will often outperform a TRF simply because since the IF transformers are never adjusted while tuning in stations, they may be adjusted very closely for one frequency and always be sensitive. If the oscillator does not track perfectly with the antenna circuit, this will not decrease volume, but will simply shift stations around just a bit, so synchronization of the condensers is not as critical. Many TRF receivers used triodes, which are not very strong amplifiers. Most superheterodynes use screen grid tubes. Many of the four tube TRF receivers, i.e. 24A, 24A, 47, 80, don't even have a primary audio amplifier, though at least the RF tubes are tetrodes (screen grid tubes). These sets cannot be expected to outperform a superheterodyne. Many designs lack an automatic volume control circuit, which greatly aids in sensitivity. I would expect a properly tuned TRF, with 3 or 4 screen grid RF tubes to perform as well as a superheterodyne with 3 or 4 RF tubes. I don't think it would perform much better. Perhaps. Anything is possible with the right parts and design. One must remember that the converter also serves as a sort of RF amplifier tube in the mixer section of a superhet.
::
::Honestly, though, I do not remember ever saying that TRF receivers outperform superheterodynes. Many times they don't. With a long tunnel of RF circuits to travel through, they can be quite selective and sensitive with all that amplification. The small 4 and 5 tube sets, especially if they utilize triodes, are not likely to outperform a superheterodyne. The thing I usually mention about TRF receivers is their superior fidelity, partially owing itself to a TRF's inability to stay perfectly synchronized. By being ever so slightly out of sync., a broader band of audio may be passed through. There are other reasons for this higher fidelity, too, such as the lack of an oscillator, so there aren't as many noises such as the harmonic notes you get when beating two frequencies together. Since they are not present, tone filtering does not have to be as severe. There's a whole lot to why they have slightly superior fidelity that I can't remember right now, but I'm sure that others in here can hit a few points. I'll have to do some reading. Also it should be remembered that many manufacturers like Grunow and Philco put out expandable IF bandwidth high fidelity superheterodyne sets. The expanded bandwidth passed as much as 10KC, which is quite fine for listening pleasure, but of course this ruined some selectivity, allowing strong local stations to overlap. That said, though, some superheterodyne AM radios are capable of the fidelity of a TRF. Of course FM radios are superheterodynes, too, but when FM was designed, they took advantage of every high fidelity feature they could and designated stations far enough apart that a wider bandwidth could be used. When AM came out originally, they crowded all the stations together in 10KC incraments.
::
::Anyway, by reading the above and realizing that a superheterodyne is no different in basic principle than a TRF, except that it uses a local oscillator to create one constant frequency so that the RF stages may be fine tuned to that one frequency, it will be understood that whether the radio be a TRF or superhet, the more stages of RF amplification, the more sensitivity and selectivity. The only real difference between the two for performance is fidelity. The superheterodyne is favorable for an inexpensive receiver because it affords much sensitivity and selectivity with fewer parts by eliminating condenser gangs and RF coils, and perhaps by eliminating a stage of RF amplificiaton because the remaining stages are tuned so well. Since it works so well for the inexpensive receiver, it is also desirable for the more expensive receiver, as here, too, the cost and parts count may be kept down to some extent.
::
::Thomas
::
:::::Thomas Dermoody made several interesting observations concerning sensitivity/selectivity issues a few weeks past. Based on my education, experience and theory, a super het should outperform a TRF hands down. I have recently restored an Edison 7R and a Majestic 90B, both TRFs. In both cases, I have peaked the trimmer caps (the sole adjustments) across the ganged tuning caps on both ends of the dial. I have also restored a Philco 48-460 6 tube super het, with a pristine BAKELITE case. My shop has a concentrically wound (approx 1 1/4 turns) #20AWG antenna at the ceiling, creating a quad approximating 15' x 20' for the TRFs only. In several instances, I've read glowing comments from Thomas about the projected performance of many old restored TRFs. In my case, the super het with its small internal case antenna, setting on the workbench, consistently outperforms the TRFs, DAY or NIGHT. Thomas, are MY OBSERVATIONS unsubstantiated?
:::
:::hi i find that a good trf set seems to pull in stations better than the superhets i have, they don't tune as sharp but they will pull in stations with more vol.. ihave a majestic 132 trf which outperforms most of my superhets.one thing though is i live in an area with few stations so the am band is not crowded maybe its my imagination but i don't think so. butch
:C'est la vie.
:
::Thomas
::Thank you for the very timely response. I didn't quote you directly as saying TRFs are better than superhets, only that you had made glowing comments about the projected (probable) performance of various TRFs, when properly restored. In comparison to what? Sorry for the misinterpretation. My observations have concluded that the superhet is both more sensitive and selective. I'm only trying to establish whether I have restored these TRFs to their full potential. My resources are limited as are my test equipments (analog VOM, DMM, restored tube tester, restored condenser tester) My superhet has no RF amp stage, but a dual ganged tuning condenser would indicate at least an antenna tuning circuit ahead of the hetrodyne converter and an oscillator tuning circuit, whereas the TRFs, (both essentially the same circuit) have a 6 gang condenser for both RF input and output tuning of 3 amplifier stages. The superhet converter(mixer) does possess gain (apparent gain) using the preferred high side injection of the local oscillator. The resultant IF waveform is always greater in amplitude (millivolts) than the RF (microvolts). The natural bandwidth limiting of properly designed IF stages greatly enhances not only the selectivity, but sensitivity as well. I guess in the Heydays of early AM radio, any radio that would tune a station or two was a modern marvel of compelling magical powers, and what is this selectivity, sensitivity thingy anyway. Nostalgia Air's presence on the web and at my finger tips has greatly enhanced my sensitivity and selectivity this year. Happy Holidays to you Thomas, and Norm, and to ALL the learned Cadre at Nostalgia Air.
:::Here's the trick, folks: The way a superheterodyne radio works is that the stages of RF amplification are all tuned to one frequency, and this never changes. A local oscillator beats a predetermined frequency with the incoming frequency to make the required Intermediate Frequency, which is tunable by the following stages of RF amplification (the IF amplifiers). Some radios have an RF preamplifier. Some of these radios have this stage tunable with an extra gang on the condenser so that it synchronizes to the antenna frequency. In this case the RF preamplifier is exactly the same as any stage in a TRF receiver. Some receivers have this stage left wide open with no tuning capabilities what-so-ever, so that it will pass all frequencies tunable by that particular radio. This cuts expense by eliminating another gang to the condenser, and often this stage of broad band preamplification will be resistance/condenser coupled, thus eliminating another expensive coil or two. This stage usually has a wave trap, though, seeing as since it is a broad band amplifier, it will easily pass the IF frequency (commonly 455KC). The wave trap is often tuned to this frequency. Since the IF transformers down the line are tuned so well, and cannot go out of sync. because they are not adjusted during the normal tuning procedure, this broad band preamplifier works well. The IF stages later will afford enough selectivity on their own.
:::
:::At any rate, with the exception of the local oscillator and that the various stages of RF amplification are fixed instead of tunable, the superheterodyne radio is not at all different in any way than the TRF receiver. The more stages of RF amplification using tuned transformers, whether these be fixed in the case of a superhet, or tunable in the case of a TRF, the more selective the radio is and the more sensitive it is. Since mechanical parts are extremely difficult to engineer to synchronize at all times, the superheterodyne will often outperform a TRF simply because since the IF transformers are never adjusted while tuning in stations, they may be adjusted very closely for one frequency and always be sensitive. If the oscillator does not track perfectly with the antenna circuit, this will not decrease volume, but will simply shift stations around just a bit, so synchronization of the condensers is not as critical. Many TRF receivers used triodes, which are not very strong amplifiers. Most superheterodynes use screen grid tubes. Many of the four tube TRF receivers, i.e. 24A, 24A, 47, 80, don't even have a primary audio amplifier, though at least the RF tubes are tetrodes (screen grid tubes). These sets cannot be expected to outperform a superheterodyne. Many designs lack an automatic volume control circuit, which greatly aids in sensitivity. I would expect a properly tuned TRF, with 3 or 4 screen grid RF tubes to perform as well as a superheterodyne with 3 or 4 RF tubes. I don't think it would perform much better. Perhaps. Anything is possible with the right parts and design. One must remember that the converter also serves as a sort of RF amplifier tube in the mixer section of a superhet.
:::
:::Honestly, though, I do not remember ever saying that TRF receivers outperform superheterodynes. Many times they don't. With a long tunnel of RF circuits to travel through, they can be quite selective and sensitive with all that amplification. The small 4 and 5 tube sets, especially if they utilize triodes, are not likely to outperform a superheterodyne. The thing I usually mention about TRF receivers is their superior fidelity, partially owing itself to a TRF's inability to stay perfectly synchronized. By being ever so slightly out of sync., a broader band of audio may be passed through. There are other reasons for this higher fidelity, too, such as the lack of an oscillator, so there aren't as many noises such as the harmonic notes you get when beating two frequencies together. Since they are not present, tone filtering does not have to be as severe. There's a whole lot to why they have slightly superior fidelity that I can't remember right now, but I'm sure that others in here can hit a few points. I'll have to do some reading. Also it should be remembered that many manufacturers like Grunow and Philco put out expandable IF bandwidth high fidelity superheterodyne sets. The expanded bandwidth passed as much as 10KC, which is quite fine for listening pleasure, but of course this ruined some selectivity, allowing strong local stations to overlap. That said, though, some superheterodyne AM radios are capable of the fidelity of a TRF. Of course FM radios are superheterodynes, too, but when FM was designed, they took advantage of every high fidelity feature they could and designated stations far enough apart that a wider bandwidth could be used. When AM came out originally, they crowded all the stations together in 10KC incraments.
:::
:::Anyway, by reading the above and realizing that a superheterodyne is no different in basic principle than a TRF, except that it uses a local oscillator to create one constant frequency so that the RF stages may be fine tuned to that one frequency, it will be understood that whether the radio be a TRF or superhet, the more stages of RF amplification, the more sensitivity and selectivity. The only real difference between the two for performance is fidelity. The superheterodyne is favorable for an inexpensive receiver because it affords much sensitivity and selectivity with fewer parts by eliminating condenser gangs and RF coils, and perhaps by eliminating a stage of RF amplificiaton because the remaining stages are tuned so well. Since it works so well for the inexpensive receiver, it is also desirable for the more expensive receiver, as here, too, the cost and parts count may be kept down to some extent.
:::
:::Thomas
:::
::::::Thomas Dermoody made several interesting observations concerning sensitivity/selectivity issues a few weeks past. Based on my education, experience and theory, a super het should outperform a TRF hands down. I have recently restored an Edison 7R and a Majestic 90B, both TRFs. In both cases, I have peaked the trimmer caps (the sole adjustments) across the ganged tuning caps on both ends of the dial. I have also restored a Philco 48-460 6 tube super het, with a pristine BAKELITE case. My shop has a concentrically wound (approx 1 1/4 turns) #20AWG antenna at the ceiling, creating a quad approximating 15' x 20' for the TRFs only. In several instances, I've read glowing comments from Thomas about the projected performance of many old restored TRFs. In my case, the super het with its small internal case antenna, setting on the workbench, consistently outperforms the TRFs, DAY or NIGHT. Thomas, are MY OBSERVATIONS unsubstantiated?
::::
::::hi i find that a good trf set seems to pull in stations better than the superhets i have, they don't tune as sharp but they will pull in stations with more vol.. ihave a majestic 132 trf which outperforms most of my superhets.one thing though is i live in an area with few stations so the am band is not crowded maybe its my imagination but i don't think so. butch