19-04-2018, 10:03 PM
The proposition that the Avantic BM612 used the Jason AM/FM2 circuit leads to the question - did the earlier Avantic AM/FM tuner also use a Jason circuit. This earlier Avantic tuner appears to have dated from 1957, being mentioned in WW 1957 June and listed in Hi Fi Year Book (HFYB) 1957:
Later it seems to have been known by the Avantic B611 name (as distinct from the later BM611), as shown in this brochure:
I doubt that one would make a connection with any Jason model based upon casual inspection of the B611 data alone, but knowledge of the likely BM612/Jason AM/FM2 connection invited a closer analysis.
Given the timing – the B611 evidently predated the AM/FM2 - then the only possible Jason circuit candidates are the Jason AM/FM and the Jasonkit Argonaut. These models shared the same faceplate and probably the same chassis dimensions, but the equipment layouts on the chassis differed somewhat. The Argonaut had the simpler circuit, suitable for home construction. Of the two, only the Jason AM/FM had a cascode FM RF amplifier and FM AFC, both features of the B611, so if there was a Jason prototype, then it was the AM/FM and not the Argonaut, although the circuitry of the latter does provide some assisting clues.
The Jason AM/FM was listed and advertised in HFYB 1956, and advertised in WW 1956 July:
Strangely, both advertisements include pictures of what looks to be the Argonaut in full receiver form, with the two small controls (volume and tone) between the two outer main controls. As far as I know, both the AM/FM, and the Argonaut in tuner form used blanking discs in place of these controls. Jason may have used a single stock picture for advertising both units. The Argonaut was described in Radio Constructor for 1956 March and April.
Information on the Jason AM/FM is scant, but what I have determined is:
It had a cascode FM RF amplifier, valve type unknown but very likely an ECC84.
It had a 2+2 gang tuning, implying an aperiodic FM input, unusual in front of a cascode stage.
It had a pentode FM mixer with a separate oscillator.
The AM mixer-oscillator was also the FM 1st IF stage, presumably a triode-heptode.
Then came a shared IF stage.
Followed by a diode demodulator for AM and a limiter and crystal diode ratio detector for FM.
It had AFC, so presumably there was an AFC reactance valve, or valve section.
It had a cathode-follower output, requiring at least a valve section.
It had a magic eye tuning indicator.
It was self-powered.
The “band selector” switch had off, AM, FM Tune and FM positions, the last-mentioned with the AFC active.
The valve function list for the Avantic B611 is not inconsistent with its having been a non-self-powered derivative of the Jason AM/FM, without the cathode follower output.
An FM front-end comprising an ECC84 RF amplifier, Z719 (EF80) mixer and B309 (ECC81) as oscillator and AFC reactance valve would have fitted the Jason description, and in fact the EF80 mixer with ECC81 oscillator/AFC was found in the later Jason FMT3.
The Argonaut used an X79, optionally an ECH81 as an AM mixer-oscillator, so it seems probable that the same was used for the Jason AM/FM. So an ECH81 in the B611 is consistent.
The Argonaut also used a W727 (6BA6, EF93) for the combined FM 2nd IF and AM IF stage. This might seem to have been an unusual choice for a domestic receiver, but Jason was initially oriented towards Osram valves, and the W727 was one of Osram’s “727” range of c.1954, all based upon American prototypes. The W727 had higher slope than say the W77 and EF41, and the EF89, comparable to the W727, was still in the future when Jason did its design work. The AM/FM probably used a W727 in this position. This appears to be confirmed by a chassis picture, which shows a cluster of three B9A-sized valves, two with screening cans, adjacent to the tuning capacitor (ECC84, EF80 and ECC81?), another B9A-sized valve between the 1st and 2nd IFTs (X79 or ECH81), but a B7G-sized valve between the 2nd and 3rd IFTs. Anyway, an EF93 in this position in the B611 is consistent.
After this there is some apparent divergence. Between the 3rd and 4th IFTs, the Jason AM/FM had a B9A valve, side-by-side with a B7G valve in a screening can. The latter was likely a D77 (EB91), serving as AM demodulator and AGC rectifier. The former I’d speculate was an ECF80, with the pentode as FM limiter and the triode as AF cathode follower. The 4th IFT probably contained crystal diode pair ratio detector. The Argonaut used a Z719 (EF80) as FM limiter, with a DH719 (EABC80) serving as AM demodulator and FM ratio detector, and 1st AF stage in receiver mode.
The Avantic B611 had an EB91 as AM detector and AGC rectifier, and an EF93 limiter, followed by a germanium diode pair as FM discriminator. An EF93 in the limiter position was certainly unusual, although not unreasonable. Beam Echo did not need a triode-pentode in this position, as the B611 did not have a cathode follower output. The choice could have been between an EF80 and an EF93, both already used in this tuner, and whilst the EF80 would seem a more likely choice, perhaps the EF93 also fitted well.
The use of a Foster-Seeley discriminator was an apparent departure from the Jason prototype. But perhaps not. The HFYB 1957 entry for the Jason AM/FM shows that by then it had a Foster-Seeley discriminator. Early on, Jason had used the ratio detector in its FM equipment, changing to the Foster-Seeley discriminator in its initial switch-tuned FM tuner. It made the change because switched FM tuners were seen as needing good AFC. And for a given signal input, the Foster-Seeley discriminator provides a higher magnitude of AFC bias than a ratio detector. Thereafter all Jason FM tuners with AFC were fitted with discriminators. I imagine that the Jason AM/FM circuit was changed from ratio detector to discriminator for the same reason.
The AM/FM had a magic eye tuning indicator, very likely a DM70, as was used on the Argonaut. Beam Echo likely saw the larger EM81 as better fitting the overall appearance of the B611. Its left-hand rotary control had four positions, off, M (for MW), T (for FM Tune), and F (for FM), essentially as was the case for the Jason AM/FM.
Thus, there is a moderate circumstantial case for saying that the Avantic B611 was a derivative of the Jason AM/FM. This is made stronger by the existence of a probable connection between the Avantic BM612 and the Jason AM/FM2.
That said, the later Avantic BM611, which was self-powered, does not appear to have had a direct connection with any of the Jason circuits. The earliest reference I have to this model is in the Audio Fair 1959 catalogue. It was the subject of a UKVRR thread about a year ago, in which a schematic was included: https://www.vintage-radio.net/forum/show...post931145. An oddity was its use of both an ECF82 (as FM mixer-oscillator) and an ECF80 (triode as AF cathode follower and pentode as AFC reactance valve). Why not two of one or the other? Overall it looked to be proximate to the B611, but with a pentode FM RF amplifier, which could be seen as a step-down from the cascode of the B611. But there are no circuit cues which suggest that it was a Jason design.
At a guess I’d say that the BM611 designation was intended to indicate performance comparability to the B611, with the added “M” perhaps indicating “mains” powered. It had a pair of neon indicators, which in this case were used to show which of the two bands was in use. Perhaps Beam Echo wanted to retain the “neon” look of the BM612, albeit in a simpler way.
Jason had rationalized its (built) tuner range in the late 1959/early 1960 period. The AM/FM models, AM/FMS2 and AM/FM2 were withdrawn without replacement. The FMT3 was retained (replaced by the FMT4 later in 1960). The Prefect and FMS2 switched tuners were withdrawn and more-or-less replaced by the Monitor switched FM and TV sound tuner, which used the same circuit as the JTV2. Having withdrawn from the AM/FM market, Jason may not have wanted to offer Beam Echo a new circuit. So either it designed its own, or found another third party supplier.
The Beam Echo Avantic range seems to have been something of a “dark horse”, with not too much information available today. So I doubt that the possible Jason connection would easily be confirmed or refuted. The circumstantial case that I have presented might well be the best that can be done. Perhaps it is enough, at least in the case of the BM612.
Cheers,
Steve
Later it seems to have been known by the Avantic B611 name (as distinct from the later BM611), as shown in this brochure:
I doubt that one would make a connection with any Jason model based upon casual inspection of the B611 data alone, but knowledge of the likely BM612/Jason AM/FM2 connection invited a closer analysis.
Given the timing – the B611 evidently predated the AM/FM2 - then the only possible Jason circuit candidates are the Jason AM/FM and the Jasonkit Argonaut. These models shared the same faceplate and probably the same chassis dimensions, but the equipment layouts on the chassis differed somewhat. The Argonaut had the simpler circuit, suitable for home construction. Of the two, only the Jason AM/FM had a cascode FM RF amplifier and FM AFC, both features of the B611, so if there was a Jason prototype, then it was the AM/FM and not the Argonaut, although the circuitry of the latter does provide some assisting clues.
The Jason AM/FM was listed and advertised in HFYB 1956, and advertised in WW 1956 July:
Strangely, both advertisements include pictures of what looks to be the Argonaut in full receiver form, with the two small controls (volume and tone) between the two outer main controls. As far as I know, both the AM/FM, and the Argonaut in tuner form used blanking discs in place of these controls. Jason may have used a single stock picture for advertising both units. The Argonaut was described in Radio Constructor for 1956 March and April.
Information on the Jason AM/FM is scant, but what I have determined is:
It had a cascode FM RF amplifier, valve type unknown but very likely an ECC84.
It had a 2+2 gang tuning, implying an aperiodic FM input, unusual in front of a cascode stage.
It had a pentode FM mixer with a separate oscillator.
The AM mixer-oscillator was also the FM 1st IF stage, presumably a triode-heptode.
Then came a shared IF stage.
Followed by a diode demodulator for AM and a limiter and crystal diode ratio detector for FM.
It had AFC, so presumably there was an AFC reactance valve, or valve section.
It had a cathode-follower output, requiring at least a valve section.
It had a magic eye tuning indicator.
It was self-powered.
The “band selector” switch had off, AM, FM Tune and FM positions, the last-mentioned with the AFC active.
The valve function list for the Avantic B611 is not inconsistent with its having been a non-self-powered derivative of the Jason AM/FM, without the cathode follower output.
An FM front-end comprising an ECC84 RF amplifier, Z719 (EF80) mixer and B309 (ECC81) as oscillator and AFC reactance valve would have fitted the Jason description, and in fact the EF80 mixer with ECC81 oscillator/AFC was found in the later Jason FMT3.
The Argonaut used an X79, optionally an ECH81 as an AM mixer-oscillator, so it seems probable that the same was used for the Jason AM/FM. So an ECH81 in the B611 is consistent.
The Argonaut also used a W727 (6BA6, EF93) for the combined FM 2nd IF and AM IF stage. This might seem to have been an unusual choice for a domestic receiver, but Jason was initially oriented towards Osram valves, and the W727 was one of Osram’s “727” range of c.1954, all based upon American prototypes. The W727 had higher slope than say the W77 and EF41, and the EF89, comparable to the W727, was still in the future when Jason did its design work. The AM/FM probably used a W727 in this position. This appears to be confirmed by a chassis picture, which shows a cluster of three B9A-sized valves, two with screening cans, adjacent to the tuning capacitor (ECC84, EF80 and ECC81?), another B9A-sized valve between the 1st and 2nd IFTs (X79 or ECH81), but a B7G-sized valve between the 2nd and 3rd IFTs. Anyway, an EF93 in this position in the B611 is consistent.
After this there is some apparent divergence. Between the 3rd and 4th IFTs, the Jason AM/FM had a B9A valve, side-by-side with a B7G valve in a screening can. The latter was likely a D77 (EB91), serving as AM demodulator and AGC rectifier. The former I’d speculate was an ECF80, with the pentode as FM limiter and the triode as AF cathode follower. The 4th IFT probably contained crystal diode pair ratio detector. The Argonaut used a Z719 (EF80) as FM limiter, with a DH719 (EABC80) serving as AM demodulator and FM ratio detector, and 1st AF stage in receiver mode.
The Avantic B611 had an EB91 as AM detector and AGC rectifier, and an EF93 limiter, followed by a germanium diode pair as FM discriminator. An EF93 in the limiter position was certainly unusual, although not unreasonable. Beam Echo did not need a triode-pentode in this position, as the B611 did not have a cathode follower output. The choice could have been between an EF80 and an EF93, both already used in this tuner, and whilst the EF80 would seem a more likely choice, perhaps the EF93 also fitted well.
The use of a Foster-Seeley discriminator was an apparent departure from the Jason prototype. But perhaps not. The HFYB 1957 entry for the Jason AM/FM shows that by then it had a Foster-Seeley discriminator. Early on, Jason had used the ratio detector in its FM equipment, changing to the Foster-Seeley discriminator in its initial switch-tuned FM tuner. It made the change because switched FM tuners were seen as needing good AFC. And for a given signal input, the Foster-Seeley discriminator provides a higher magnitude of AFC bias than a ratio detector. Thereafter all Jason FM tuners with AFC were fitted with discriminators. I imagine that the Jason AM/FM circuit was changed from ratio detector to discriminator for the same reason.
The AM/FM had a magic eye tuning indicator, very likely a DM70, as was used on the Argonaut. Beam Echo likely saw the larger EM81 as better fitting the overall appearance of the B611. Its left-hand rotary control had four positions, off, M (for MW), T (for FM Tune), and F (for FM), essentially as was the case for the Jason AM/FM.
Thus, there is a moderate circumstantial case for saying that the Avantic B611 was a derivative of the Jason AM/FM. This is made stronger by the existence of a probable connection between the Avantic BM612 and the Jason AM/FM2.
That said, the later Avantic BM611, which was self-powered, does not appear to have had a direct connection with any of the Jason circuits. The earliest reference I have to this model is in the Audio Fair 1959 catalogue. It was the subject of a UKVRR thread about a year ago, in which a schematic was included: https://www.vintage-radio.net/forum/show...post931145. An oddity was its use of both an ECF82 (as FM mixer-oscillator) and an ECF80 (triode as AF cathode follower and pentode as AFC reactance valve). Why not two of one or the other? Overall it looked to be proximate to the B611, but with a pentode FM RF amplifier, which could be seen as a step-down from the cascode of the B611. But there are no circuit cues which suggest that it was a Jason design.
At a guess I’d say that the BM611 designation was intended to indicate performance comparability to the B611, with the added “M” perhaps indicating “mains” powered. It had a pair of neon indicators, which in this case were used to show which of the two bands was in use. Perhaps Beam Echo wanted to retain the “neon” look of the BM612, albeit in a simpler way.
Jason had rationalized its (built) tuner range in the late 1959/early 1960 period. The AM/FM models, AM/FMS2 and AM/FM2 were withdrawn without replacement. The FMT3 was retained (replaced by the FMT4 later in 1960). The Prefect and FMS2 switched tuners were withdrawn and more-or-less replaced by the Monitor switched FM and TV sound tuner, which used the same circuit as the JTV2. Having withdrawn from the AM/FM market, Jason may not have wanted to offer Beam Echo a new circuit. So either it designed its own, or found another third party supplier.
The Beam Echo Avantic range seems to have been something of a “dark horse”, with not too much information available today. So I doubt that the possible Jason connection would easily be confirmed or refuted. The circumstantial case that I have presented might well be the best that can be done. Perhaps it is enough, at least in the case of the BM612.
Cheers,
Steve
