Some time ago, I came across a German site offering brand new IF transformers. The parts intended for use in P2P projects were of an "unusual" construction. The coils were mounted on PCB material, which went through a slot in the chassis. A cylindrical shield went over the coil board, with the board sticking through a slot in the top. A plastic wedge inserted on the top's outside held the whole assembly together.
For the life of me, I can't track this vendor down. Repeated tries with Google have been unproductive.
Can any member provide a URL?
TIA.
For the life of me, I can't track this vendor down. Repeated tries with Google have been unproductive.
Can any member provide a URL?TIA.
Thanks guys! perfect. I have been thinking about building an all tube tuner for a while and IF transformers are the major stumbling block. May even build a multipath scope into it using a small 1 inch CRT after the subject came up in another thread. Not sure if you guys have seen Patrick Turners design:
am-fm-radio-tuner-multiplex-decoder
Cheers
Matt.
am-fm-radio-tuner-multiplex-decoder
Cheers
Matt.
Patrick Turner's MPX decoder is of considerable interest to me. For some time, I have been kicking the idea of a "100%" tubed FM tuner around and, as you said, IF "cans" are a major impediment.
FWIW, my general plan of attack is a cascoded 6922 as the TRF front end, a 6U8 local oscillator/mixer, 4X 6AU6 IF stages, and a 6BN6 gated beam detector. The MPX decoder would employ a 6JU8 quad diode in the ring demodulator. Signal strength and tuning accuracy indications would be via a 6AF6 twin "magic eye".
If an AGC issue rears its ugly head, a 6BZ6 could be used, instead of a 6AU6, in the IF strip.
FWIW, my general plan of attack is a cascoded 6922 as the TRF front end, a 6U8 local oscillator/mixer, 4X 6AU6 IF stages, and a 6BN6 gated beam detector. The MPX decoder would employ a 6JU8 quad diode in the ring demodulator. Signal strength and tuning accuracy indications would be via a 6AF6 twin "magic eye".
If an AGC issue rears its ugly head, a 6BZ6 could be used, instead of a 6AU6, in the IF strip.
Far be it for dampening your enthusiasm for "scratch building" an FM tuner but besides the IF (and multiplex) transformer issues there is the "front end".
Unless you are going to try multiple varicap diodes (and their attendant tracking issues) you would need a 3 to 5 section variable tuning capacitor. Try to find one of those these days. Then, how do you plan to mechanically operate it - and what kind of dial might you use? Without multiple, tunable RF stages in the front end, tubes can have serious problems with intermod distortion in urban environments
If you can "let go" of total scratch building, you could look into scavenging sub-assemblies (front ends, IF transformers) from scrap or non-working tuners. Both Fisher and Scott made some nice tubed front end modules - Fisher used multiple nuvistors. The Dyna FM-3 has a very decent IF /detector board.
Regarding tubed-multiplex decoders, the designs I've seen and used suffered from limited separation, especially in the high frequencies, which seemed to make the hall "V" shaped and added distortion. The second-generation decoder chips are fine from that perspective and don't need weird coils. Get the low level audio signals out of them, bypass any internal op amps, and follow up with a tube-based line amp.
Depending upon the type of detector you plan on using, you may also have to think about having multiple limiting stages.
Then there is the alignment issue - especially in the IF strip. Getting multiple transformers to "line up" (overlapping wide band designs or stagger tuning narrow band designs really requires a swept signal source to do it right). That's why designers dropped tuneable coils, like hot potatoes, for ceramic filters.
For a number of years I played FM reception games with surveillance receivers. Most of them covered the commercial FM band and earlier ones used nuvistors in the front end if not throughout, with 3 to 5 stages of permeability tuning (tuning the L instead of the C - like old car radios). Nems-Clarke, Communication Electronics Inc (CEI) made nice tubed units. As there were typically lots of unnecessary circuitry in these receivers, DIY scavenging and simplifying is a distinct possibility.
But with the continuing degradation of the medium's sound quality, I have basically given up on FM.
Have fun in any case.
Charles
Unless you are going to try multiple varicap diodes (and their attendant tracking issues) you would need a 3 to 5 section variable tuning capacitor. Try to find one of those these days. Then, how do you plan to mechanically operate it - and what kind of dial might you use? Without multiple, tunable RF stages in the front end, tubes can have serious problems with intermod distortion in urban environments
If you can "let go" of total scratch building, you could look into scavenging sub-assemblies (front ends, IF transformers) from scrap or non-working tuners. Both Fisher and Scott made some nice tubed front end modules - Fisher used multiple nuvistors. The Dyna FM-3 has a very decent IF /detector board.
Regarding tubed-multiplex decoders, the designs I've seen and used suffered from limited separation, especially in the high frequencies, which seemed to make the hall "V" shaped and added distortion. The second-generation decoder chips are fine from that perspective and don't need weird coils. Get the low level audio signals out of them, bypass any internal op amps, and follow up with a tube-based line amp.
Depending upon the type of detector you plan on using, you may also have to think about having multiple limiting stages.
Then there is the alignment issue - especially in the IF strip. Getting multiple transformers to "line up" (overlapping wide band designs or stagger tuning narrow band designs really requires a swept signal source to do it right). That's why designers dropped tuneable coils, like hot potatoes, for ceramic filters.
For a number of years I played FM reception games with surveillance receivers. Most of them covered the commercial FM band and earlier ones used nuvistors in the front end if not throughout, with 3 to 5 stages of permeability tuning (tuning the L instead of the C - like old car radios). Nems-Clarke, Communication Electronics Inc (CEI) made nice tubed units. As there were typically lots of unnecessary circuitry in these receivers, DIY scavenging and simplifying is a distinct possibility.
But with the continuing degradation of the medium's sound quality, I have basically given up on FM.
Have fun in any case.
Charles
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Voila! Look here. Add a vernier dial, which is available in both NOS and current production, and the tuning issue is disposed of.
Yes, alignment is a PITA, but much of the superior sound of tube tuners comes from the transformer coupled IF strip. I might consider a wide bandwith ceramic filter to couple the last IF stage to the detector.
Stellavox, I agree with your points and I know it is no easy task to build a decent FM tuner. That is the reason I would like to build one. Allignment is not an issue for me as I have the kit and can build anything I don't have. That's the fun part for me. I will use all tube including the MPX decoder just to see if I can get it to work well. If not there is always the MC1310 for stereo decoding but that is cheating and I won't learn much. Multi section variable capacitors are no problem as I have several I use for tweaking global feedback around audio amps, theres loads on eBay too. As for a scale, well a nice nixie frequency counter using 74141s (or the Russian version) and some other logic for prescaling etc would fit the bill nicely.
Cheers
Matt.
Cheers
Matt.
I have my own project entirely designed following the Langford Smith book, using ECC84 as RF, ECF801 as mixer, EF183/4 as FI, 6AL5 detector, EBF81 and 7360 for the MPX and a EM84 as tuner indicator. The tuning mechanism is a novelty design of my own, based in the concepts of an old TV tuner called "Inductuner" that is explained in a book, basically is a coil which is controllably coupled to a short circuited wire turn that in turns modify the inductance and the frequency. I have coil formers from TV scrap with the slug inside.
Finally, a ECF82 ats as a AFC. I have the project in txt ASCII format.
Finally, a ECF82 ats as a AFC. I have the project in txt ASCII format.
Nixie frequency readout is also covered in das UKW Projekt. But impossible to do if you want to keep it all void state. I'd settle for a nice mechanical digital readout à la R390A. If you can get one (old odometer?). And it'll be a bitch to calibrate.
Hey,
Really enjoying the creativity popping up here.
Here's a thought - from a "front end" perspective, there are transistorized FM front ends showing up regularly on Ebay - from Marantz (et al) tuners. Many are 4 gang. Could "retro engineer" one of these "back" to tubes - nuvistors instead - small and might be able to fit near the existing FET's. I believe I remember that certain nuvistors used to be available from Russian sources with lead wires instead of pins - or could try pencil tubes (wire connections) if any were designed for RF.
Same concept could be applied to the IF strip.
For a readout - relatively inexpensive frequency counter are around on various ham radio-related sites. Most have a programmable frequency offset so you can compensate for (add/subtract) the IF frequency.
Just depends on how far one wants to take this "DIY Thaang"
Charles
Really enjoying the creativity popping up here.
Here's a thought - from a "front end" perspective, there are transistorized FM front ends showing up regularly on Ebay - from Marantz (et al) tuners. Many are 4 gang. Could "retro engineer" one of these "back" to tubes - nuvistors instead - small and might be able to fit near the existing FET's. I believe I remember that certain nuvistors used to be available from Russian sources with lead wires instead of pins - or could try pencil tubes (wire connections) if any were designed for RF.
Same concept could be applied to the IF strip.
For a readout - relatively inexpensive frequency counter are around on various ham radio-related sites. Most have a programmable frequency offset so you can compensate for (add/subtract) the IF frequency.
Just depends on how far one wants to take this "DIY Thaang"
Charles
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Best resource I can think of for one topic is "FM Multiplexing for Stereo" By Leonard (Len) Feldman - Howard Sams & Co, 1962. Thorough coverage of history, theory, manufacturers approaches / circuits (both generators and decoders) and alignment up through that time. Most of the decoders were really cost constrained.
Did have a great book on FM receiver theory and design but damned if I can find it or remember the title. Was from the 50's or 60's.
O yeah, regarding inductive tuning, Mallory (the capacitor company?) made those "Inductuners"; multiple variable inductances "tuned" by a single shaft. These were used in the surveillance receivers and a few (tubed) TV front ends. Per my memory, only REL (Radio Electronics Labs) used inductive tuning in any commercial FM receiver.
Charles
Did have a great book on FM receiver theory and design but damned if I can find it or remember the title. Was from the 50's or 60's.
O yeah, regarding inductive tuning, Mallory (the capacitor company?) made those "Inductuners"; multiple variable inductances "tuned" by a single shaft. These were used in the surveillance receivers and a few (tubed) TV front ends. Per my memory, only REL (Radio Electronics Labs) used inductive tuning in any commercial FM receiver.
Charles
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Hey Charles, it's funny you and Osvaldo have brought up the subject of inductive tuners
I just grabbed an old Dynatron UK made console system that a friend had in his garage. It is transistor and uses Mullard modules for the tuner. The presets use inductive tuning so I may well use these for my tuner at least so I can have the convenience of a few presets. The rest of it is pretty normal late 60s early 70s junk apart from the case which is quite nice veneer covered ply.
Cheers
Matt.
I just grabbed an old Dynatron UK made console system that a friend had in his garage. It is transistor and uses Mullard modules for the tuner. The presets use inductive tuning so I may well use these for my tuner at least so I can have the convenience of a few presets. The rest of it is pretty normal late 60s early 70s junk apart from the case which is quite nice veneer covered ply.
Cheers
Matt.
@Stellavox: Nuvistors are excellent devices. Alas they're not drop-in replacements for MOSFETs or transistors because it needs neutrodynization (neutralization) as you want to use it common cathode. The high C(ag) will make a fine oscillator. Best bet is a cascode with dedicated VHF double triode (ECC2000!). Then a pentode/triode (ECF80) as mixer/oscillator. For the IF strip use regular pentodes like EF80 or 6AU5. EF89 is intended for IF use in European AM/FM radios.
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