Jason AM / FM Tuner

[amandamalc]

I recently obtained this tuner, which seems relatively intact with a view to repairing it. However, there appears to be very little information out there on this particular model. I know it is not the later 'Argonaught' as I have a print out of the Argonaught manual, so it might be an earlier model? (The big smoothing cap shows a date code of 1956) This one has the same gold front panel with two tuning scales (with two blanked off holes between the two big knobs) and a total of seven valves. Correction - TWO are missing :-( The current line-up anticlockwise from the tuning cap. is an X719 (EF80), X719 (EF80), X79 (ECH81), 6BA6, then an empty B9A holder, another Z719 (EF80) then lastly, another blank holder in the far corner next to the mains transformer. OK, so this last one is almost certainly an EZ80, but what about the other one Reading other messages in this forum about Jason tuners, along with other brief 'mentions' about this unit on other sites, I've narrowed this down to possibly an ECC81 or possibly an EABC80? As there don't appear to be any diodes visible under the chassis, this may explain the later, but it would be nice to know! Any help here gratefully received.

[Synchrodyne]

The tuner at interest might be the Jason AM/FM. This shared the same fascia and chassis base as the Jasonkit Argonaut, but was otherwise quite different. It might have slightly postdated the Argonaut. The first advertisement I have seen for the AM/FM is in WW 1956 July. Curiously, the advertisements for the AM/FM – and the HFYB 1956 entry – picture the Argonaut, with a full complement of knobs.

I have not seen a circuit or a valve line-up for the Jason AM/FM – it is about the most obscure of the Jason tuners. But here is a transcript of a what was a barely readable copy of one page of a (multipage) descriptive leaflet:

>>>>>>>>>>

THE JASON AM/FM TUNER WITH AUTOMATIC FREQUENCY CONTROL


This tuner is primarily designed as an excellent self-powered F.M. tuner, though the audio xxxxx performance is in no way spoiled by the combined operation of the xxxx stages.….


…..A cathode follower output stage with gain control enables the output voltage to be set to the optimum whatever amplifier is used. Interstation noise is suppressed


This tuner is suitable for use with any amplifier on the market.


This tuner is very sensitive and may be expected to give good results up to 60 miles from the station under bad conditions – under good conditions a range of 60-100 miles from the station may be expected. The scale is calibrated both in megacycles and station names and will receive any of the present or proposed B.B.C. stations in any part of the country.

The stages are as follows:-

The R.F. stage is a low noise twin triode “cascode” input. A separate oscillator with a pentode mixer achieves a good gain with minimum noise. The first I.F. stage is also the medium wave frequency changer stage. The next I.F. stage functions as both F.M. and M.W. I.F. stage, the former feeding a limiter while the latter is coupled to a detector diode. A second diode is used for quieting the tuner between stages. A low distortion Ratio Detector circuit follows the limiter and crystal diodes are used to avoid valve hum pick-up.

The sensitivity on F.M. is 10 microvolts for 40 db quieting i.e., a minimum good quality signal. The frequency coverage is 88-100 mc/s. The medium wave sensitivity is 50 microvolts and the range covered is 195 – 560 metres.

Operating instructions – Two controls are provided – the right-hand being the spin drive tuning control – the left-hand control has four positions indicated by a pointer at the left-hand side of the dial. The first position is the ‘off’ position, the second m.w. and third the ‘F.M. tune’ position. This position prevent the automatic frequency control from operating and the station may be tuned either by ear or reference to the magic eye tuning indicator. Switching into the fourth position allows the automatic frequency control circuit to correct any tuning error.

Physical dimensions – front panel size 11½” x 67/8“ – hole required in cabinet 10½” x 6¼“ – depth behind front panel 8”.

Price £20.12. 6. plus P. Tax £8. 1. 0.
Packing case £2 extra (reimbursable) Postage 7/6 extra.


The Jason Motor & Electronic Co., 328, Cricklewood Lane, London, N.W.2. (HPB. 7050).

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The Jason AM/FM was unusual in British practice in having a cascode RF amplifier (although such was more common in US practice).

The AM/FM was superseded in late 1957 by the AM/FM2, which had a three-gang cascode front end, using an ECC84. It would seem that there is some chance that the same RF valve had been used in the AM/FM front end.


In general, the Jason/Jasonkit tuner range was quite complex. Jason and Jasonkit products with the same designation did not necessarily have the same circuits – although sometimes they did - and often they had different cases. And sometimes when the circuitry was the same, the Jason and Jasonkit versions had different names. For example, the similarly named Jason FMT3 and Jasonkit FMT3 had different valve lines up, but the differently named Jason Monitor and the Jasonkit Mercury II (as distinct from the original Mercury) shared the same circuit.

Jason appears to have started with Osram valves, its original FM tuner using four Z77, with the fringe area version adding a Z719. The appearance of the 6BA6 in the AM/FM and Argonaut may have been a result of Osram’s promotion of its “727” series, in which the 6BA6 was the W727. That it had a higher slope than its own W77 might have been a factor in its choice by Jason. But thereafter Jason appeared to move towards Mullard valves. For example, the Argonaut was specified to use either an X79 or an ECH81 as an AM frequency changer (with appropriate circuit adjustment for each), and I suspect that the same was true for the AM/FM.


Cheers,

[Synchrodyne]

By way of an indirect approach, there is very strong circumstantial evidence that the Beam Echo Avantic Type 612 (aka BM612) AM-FM tuner was simply a clone of the Jason AM/FM2, in a different case. Using that as a starting point, then it is plausible that the earlier Avantic B611 (as distinct from the later BM611) was also based upon the Jason AM/FM, albeit probably with some changes. Thus the valve line-up for the B611, included in the attached brochure page, might serve as a general guide for the Jason AM/FM, at least until the data for the latter comes to light. Certainly that the Avantic B611 used the ECC84 cascode valve and the EF93 (6BA6, W727) would be an unusual coincidence if there were no connection.


Cheers,