Jason FM/TV sound tuner

[signalman4]

   
Hi all,
Please can anyone help with info for a pretty little Jasonkit TV/FM Tuner in a light green metal case.  
It is different from the already known FMT1,FMT2 or FMT3.

It has a EM81 magic eye and a turret tuner reminiscent of the ones in TV sets but has a ECC84 and a ECF80 rather than the P range used in TV tuners.
There is also a EF89 or two (maybe one is supposed to be an EF80!)

It covers TV band I and band III also Light, Third and Home FM channels.
I have been unable to find anything about this on the web so if someone has the manual or other info, it would be great.

cheers,
SM4

[Synchrodyne]

That would be the original version of the Jason/Jasonkit JTV, available both built and in kit form, and I think released later the second part of 1958, concurrently with the Jason/Jasonkit FMT3.  I think that it lasted about a year before being replaced by the better-known Jason/Jasonkit JTV2, which then stayed available until the end of Jason.  The JTV2 used a modified Fireball tuner, and had AFC but not a tuning indicator.  The JTV2 circuit (less the AM noise limiter diode) was also used in the Jasonkit Mercury 2/Jason Monitor.  In the Jasonkit case, it replaced the original FM-only Mercury.  In the Jason built series, it arrived at a time when all of the previous Jason switched FM tuners had gone.

The original JTV and any detailed information on it appear to be very scarce, whereas that for the JTV2 and Mercury 2/Monitor is reasonably available.  All I have is the valve line-up for the JTV, which as you have already stated, was ECC84, ECF80, EF89, EF80, EM81, EZ80.  No doubt it had a pair of crystal diodes for FM demodulation, probably a ratio detector given that there were only two IF stages.  (Jason used both this and the Foster-Seeley discriminator according to situation.)  AM demodulation might have used another diode, although the JTV2 used the limiter grid as the source of demodulated AM.  But then it had three IF stages of which the third was purely a limiter.  In the case of the JTV, probably the EF80 was an amplifier/limiter.

Steve P.

[ppppenguin]

I had a JTV2 many years ago. It was pretty horrible as far as I can remember.

[Terry]

... but has a ECC84 and a ECF80 rather than the P range used in TV tuners ...

That is because Jason used a parallel heater supply with 6.3V valves (E = 6.3V) whereas it was easier for TV designers to have a series heater chain across the mains, so all the valves had to be made to pass the same current - in this case 300mA (P = 300mA). 

Some of the heater voltages in these heater chains were correspondingly high as greater power was required in timebases and so on. 

A full breakdown of the ECF80 code is:

E = 6.3V heater
C = triode
F = pentode
80 = B9A base

You can find full details of the numbering system at:

https://en.wikipedia.org/wiki/Mullard%E2...esignation

[ppppenguin]

A full breakdown of the ECF80 code is:

E = 6.3V heater
C = triode
F = pentode
80 = B9A base

Strictly speaking 8 = B9A base. The 0 is an arbitrary designation by the manufacturer to distinguish between different 6.3V triode pentodes on B9A bases.

It was probably sensible for Jason to use 6.3V parallel heaters for their tuners. A live chassis approach would have been impractical though they could have used P series valves with a suitable winding on the mains transformer to supply the total heater voltage. I suppose they designed their tuners as an adjunct to their amplifiers such as the J2-10. The amps used 6.3V heaters so that's what the designers were familiar with.

[Terry]

Actually, we are both wrong! I should have written 8x or 80 - 89 as a single digit implies the old side contact base, although all the examples I can think of end in 1 - I doubt if there were 8 different versions of any valve type in those days!

EDIT: Actually, the source I gave says:

1-9 Pinch-type construction valves, mostly P8 bases (P base, 8-pin side-contact) or European 5-pin (B base) and various other European pre-octal designs.

For some reason, I couldn't get the link to work just now - it threw up a DNS error! However, if I only past in the bit that starts with wikipedia, it brings up the page and changesthe url to the version I posted!

Is that weird, or not?

[ppppenguin]

And 3 digit endings were often used for professional valves (as against those intended for domestic use)

[Terry]

Aah! Sussed it, I think!

The correct link is https://en.wikipedia.org/wiki/Mullard%E2...esignation but when I created it, the forum obligingly stuck an erroneous http:// in front of it!

Hopefully, this time it will work!

https://en.wikipedia.org/wiki/Mullard%E2...esignation

[Alistair D]

And 3 digit endings were often used for professional valves (as against those intended for domestic use)

Perhaps in the early days. Later TV valves were often 3 digit e.g.
PL519
PL508
GY501
PFL200
PCL805
PY800
to name a few.

Al

[Synchrodyne]

Of course, the use of 6.3-volt heater valves was the norm for hi-fi equipment including tuners, and the Jason JTV followed this norm.  The JTV and JTV2 were both self-powered, but some Jason equipment, such as the Mercury 2/Monitor was externally powered, requiring both HT and LT supplies.  Where a suitable power supply from an associated amplifier was not available, Jason offered a power supply unit, both in built and kitset form.

As far as I know, proprietary TV front ends were usually available with both conventional 6.3-volt heater valves and series-string 300 mA heater valves.  In fact, in the USA, the makers catered for both 600 mA and 450 mA series strings.  In this part of the world, most valved TV receivers had “proper” power supplies, with double-wound power transformers, and used 6.3-volt valves.  Thus, the ECC84 and ECF80 were commonly found in front ends.  So, there was really nothing strange about Jason’s use of the ECC84 and ECF80 in the JTV.  Both were also found in UK FM tuner and receiver practice.

Re information about the JTV, apparently Hi-Fi News (HFN) ran an article about it when it was released.  HFN claimed to have been instrumental in persuading Jason to develop the JTV and then offer it in both built and kitset forms.  I don’t know which HFN issue it was in, but I would guess somewhere in the second half of 1958.  How much detail is also unknown, but I should expect at least a circuit description if not a schematic.  Unfortunately, back issues of HFN are not readily available.  The front end circuit might be available separately if the make and model of the unit are known; Cyldon, Plessey, AB Metal Box would be candidates amongst others.  As mentioned, for the JTV2, Jason used the American-origin Fireball front end, which I think was made in the UK by AB Metal Box.  So maybe the latter had also been the supplier of the regular turret used in the JTV.  It would have been modified to provide a 10.7 MHz IF output on TV sound as well as FM, but probably was otherwise standard, unlike the JTV2 case, where the front end was significantly modified.

Given that the JTV had a fairly short production life, I suspect that it was not entirely satisfactory, and may have been wanting in the gain and stability departments.  Hence the JTV2, with greater IF gain (although probably with less front end gain) and AFC.

Re Pro-Electron valve designations, three-digit suffixes appear to have arrived in the late 1950s, presumably because there were not enough in the allocated two-digit ranges.  Early examples include the EF183, EF184 and ECC189.  And three-digit suffixes in the 500 series appear to have been used for magnoval-based valves from the beginning of that type, starting with the EL500, which was a very common TV valve here.

Steve