UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 12th Aug 2019, 2:10 pm   #21
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,550
Default Re: Jason FM Tuner

I thought there were FM transmissions in 1954....at least in the London area. Not sure if it was the full service but I think Wrotham was running by then. In fact I think Bush produced their first FM radio in 1954
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is offline  
Old 12th Aug 2019, 4:14 pm   #22
barrymagrec
Octode
 
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,552
Default Re: Jason FM Tuner

There were experimental AM and FM VHF transmissions from Wrotham starting in 1951, the proper FM service started in 1955
barrymagrec is offline  
Old 13th Aug 2019, 3:14 am   #23
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Jason FM Tuner

The Wrotham experimental FM transmissions appear to have inspired sufficient listener interest to justify the (assumed small-scale) production of tuners by some of the hi-fi industry.

Amongst the early movers were Lowther, whose tuner was advertised at least as early as 1953 June and I think might have been available a little earlier than that. Chapman advertised its FM81 model 1953 November. Sound Sales advertised in 1954 June and Goodsell in 1954 September. So Jason, which also announced c.1954 September, was reasonably early but not excessively so. The prototype Quad FM tuner was shown in mid-1952, although it was not put into production until 1955.

The TAC decision in favour of a VHF-FM service was accepted by the PMG in 1954 February, so from then onwards the equipment manufacturers were in a position to plan with some confidence for the introduction of FM tuners and receivers. This also included making provision for the easy addition of FM units to existing component assemblies. For example, in 1954 September, Armstrong released its FC48 (replacing the FC38) and EXP125C (replacing the EXP125/A) chassis, both AM-only and both of which had an input for and a power supply outlet for an FM tuner, which later materialized as the FM56. Also in 1954 September the Dynatron T139 had a similar provision, in this case to allow connection of the following FM1 switched FM tuner.

Some of the early FM tuners also had provision for receiving the Wrotham VHF-AM broadcasts, including the Lowther, Chapman and Sound Sales models. There is indirect evidence that the prototype Quad FM also had this facility.

But even before Wrotham came on air, the Alexandra Palace experimental transmissions (FM and AM) had created some interest. (These were mentioned in WW 1949 June, p.221.) At Radiolympia 1949, both HMV and K-B showed FM receivers. The HMV 1250 would probably have bettered most, if not all of the early British production FM receivers, and may have been in the same class as the Hacker Mayflower of the early 1960s. The K-B model had crystal controlled switched tuning, and there was also an adaptor version (i.e. a tuner) for use with existing receivers. At the end of 1949 English Electric also released a TV-FM receiver. As far as I know, none of these had provision for VHF-AM. At the time, the manufacturers may have been working on the assumption that any future VHF radio service would be FM not AM, as was the case elsewhere in the world and as had been indicated in the 1946 BBC report. By 1953, the risk of VHF-AM must have been seen as a material one.

Anyway, against that background, Jason’s market entry timing looks to have been about right for a company that wanted to become known as an FM tuner specialist. It was when a national FM service was definite, but ahead of the crowd, as it were. And the Wrotham experimental FM transmissions (I don’t know when AM was stopped) were ongoing until the start of regular service in 1955 May.

Whether any of the early UK entrants into the FM tuner market were thinking much about the export market is unknown. At the time that market would have been mostly the USA and Canada, and Germany and Italy. By then some of the amplifier manufacturers were establishing themselves in the US market, so FM tuners would have been desirable additions in the not too distant future. But most of the early FM tuners appear to have had rather restricted tuning ranges, stopping at 100 MHz or sometimes lower, that would have made them unsuitable for the North American market.


Cheers,
Synchrodyne is offline  
Old 13th Aug 2019, 4:07 am   #24
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Jason FM Tuner

Quote:
Originally Posted by PJL View Post
I wonder why they chose point contact diodes, but I guess 1954 was before the first transmission so they were probably modelling the design on TV's and the EABC80 would not have been in volume production.
I’d say that the industry was split between using germanium crystal diodes, such as the GEX34, and thermionic diodes, such as the EB91, for FM demodulator service. Jason chose the crystal diode approach, commenting that in its initial design, thermionic diodes were less suitable because of harmonic feedback along the heater line. Presumably in a home constructor design, avoidance was a better strategy than suppression. Jason stayed with the crystal diodes throughout with I think just one exception, and that was the Jasonkit Argonaut, which used a DH719 (or EABC80 or 6T8) as FM demodulator. Whilst it started with the ratio detector, it did later use, although not exclusively so, the Foster-Seeley discriminator, possibly because it provided a higher AFC bias. (Though the FMT4 used a ratio detector with a transistor to amplify the AFC bias.)

On the other hand, Chapman started with the EB91 as a ratio detector and then used that form in all of its valve-era FM and AM-FM tuners. Lowther used two diodes of the EABC80 as a Foster-Seeley discriminator in its initial (1953) tuner. I don’t know about the Mk II model, but the Mk III and Mk V both used the 6AL5 (EB91) as a discriminator. Leak started with the EB91 as discriminator in 1955, but switched to crystal diodes with the Troughline II in 1959.

Lowther’s use of the EABC80 suggests that this valve was at least available in the UK in 1953, if not yet widespread. The 6T8 (similar, but not identical) was evidently available from Brimar in 1951, and for example was used in the Spencer (BBC) FM receiver published in WW 1951 November.

Valve type initial availability appears to have varied by region and/or country. For example, the EBC81, as the 6BD7, was available in Australia from c.1950, but not in the UK until 1955 or so, where the EBC41 filled the same role. (Hence the use of the EBC41 in the Pye FenMan II, in an otherwise all-noval line-up).


Cheers,
Synchrodyne is offline  
Old 13th Aug 2019, 10:45 am   #25
Peter.N.
Dekatron
 
Join Date: Jul 2008
Location: Charmouth, Dorset, UK.
Posts: 3,601
Default Re: Jason FM Tuner

We had at least test transmissions from Wrotham Hill in 1954.

Peter
Peter.N. is offline  
Old 13th Aug 2019, 12:04 pm   #26
vidjoman
Dekatron
 
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,315
Default Re: Jason FM Tuner

I'm sure I built a Jason with the Christmas money I got in 1954. Not supplied as a complete kit but the local spares dealer got the metalwork and IF trannys from Jason and added his own set of r's & c's. The amp I had at the time, also home built, struggled with the heater supply to power the FM tuner as well and ran very hot, so the tuner was then given a separate power supply.
I lived in Dartford at the time so was very close to Wrotham and could get good signals on a piece of wire as an aerial.
vidjoman is online now  
Old 13th Aug 2019, 1:44 pm   #27
Boulevardier
Octode
 
Join Date: Sep 2017
Location: Bristol, UK.
Posts: 1,642
Default Re: Jason FM Tuner

I also lived in Dartford in 1954, and, from its higher parts, Dartford must be pretty well line-of-sight to Wrotham.

Mike
Boulevardier is offline  
Old 13th Aug 2019, 4:18 pm   #28
vidjoman
Dekatron
 
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,315
Default Re: Jason FM Tuner

Up on the rooftop, near Dartford heath, I could see Crystal Palace TV transmitter but not Wrotham - there were some slightly higher houses in the way but they didn't affect the FM transmissions.
vidjoman is online now  
Old 20th Aug 2019, 2:24 am   #29
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Jason FM Tuner

Quote:
Originally Posted by turretslug View Post
The use of an EF80 RF stage and EF91s elsewhere make this tuner iteration an illustrative sidebar to the current "EF91 to EF80" thread!
Indeed the Jason literature provides quite good insight into the differences between the EF91 and the EF80.

As noted, the original Jasonkit local area FM tuner circuit was designed for simplicity and stability, and used four Z77 (EF91) and a pair of germanium diodes. It had RF amplifier, autodyne mixer, IF amplifier and limiter stages using the Z77, with AGC from the limiter grid to the RF amplifier, and a ratio detector.

In respect of the Jasonkit fringe area version it was stated: “The RF valve has been changed to an Osram Z719 to increase the gain before the frequency changer.” Also, another IF stage was added, using a Z77.

This established a pattern in which future Jason FM tuners were either of the local area type with two IF stages or of the fringe area type with three IF stages.

In respect of the local area model, it was said: “The Z719 may be used in the RF stage as in the fringe area version described. The aerial coil as described previously is suitable for this valve. If a 6AK5 is employed in the RF stage, this coil is not suitable because the grid capacity is lower. As the input impedance is higher, a looser coupling of the aerial coil may be used.”

This was apparent recognition that some constructors might want to use the 6AK5 (EF95) for even better performance.

The EF91 remained as the standard valve in the original local area tuner, and in its later Jasonkit FMT1 form. The Jasonkit FMT2 was a self-powered, cased version of the FMT2 with EF80 valves in all positions. As well as providing greater RF gain, the EF80 also allowed slightly greater IF gain.

Otherwise, from c.1956, the EF80 became Jason’s standard high-slope, sharp cutoff pentode, although it also used the pentode section of the ECF80, probably to minimize the valve count in some models where a triode or triodes were also required. It also appears that the EF80 was also used in some Jasonkit models in positions where the EF89 was used in the corresponding Jason (built) model.

For example, the Jasonkit FMT3 – whose circuit details are readily available - used the EF80, five of them, in all signal positions, namely RF amplifier, mixer, IF amplifier, 1st limiter and 2nd limiter. The oscillator and AFC functions were handled by an ECC81. (The EF80 mixer and ECC81 oscillator/AFC combination had first appeared in the Jason AM/FM of 1956.) On the other hand, the Jason FMT3 – whose full circuit details have not emerged - had an EF80 RF amplifier, ECF80 pentode section as mixer, EF89 IF amplifier, and ECF80 pentode sections as 1st and 2nd limiters. Of the three available ECF80 triodes, I’d guess that one was the oscillator, one was the AFC valve and one was the AF cathode follower. Given that the Jason FMS2, AM/FMS2 and AM/FM2 all had cathode follower outputs, it seems likely that the Jason version of the FMT3 was also so-equipped. But none of the Jasonkit models had this facility.

The Jasonkit Mercury and Jason FMS2 were also more-or-less counterparts. The former had four EF80s (RF, IF and two limiters) and an ECF80, the latter serving as autodyne mixer and AFC valve. The FMS2 differed in having an EF89 IF amplifier and an ECF80 pentode as 2nd limiter, its triode used as a cathode follower. Possibly Jason wanted to minimize the number of valve types used in the Jasonkit models, hence its choice of the EF80 over the EF89. However, the use of the EF89 in the Jasonkit versions of the JTV and JTV2 was probably unavoidable.


Cheers,
Synchrodyne is offline  
Old 20th Aug 2019, 7:26 pm   #30
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Jason FM Tuner

I have cleaned it up, replaced the hunts capacitor which served as de-emphasis and should have been ceramic/mica, replaced the previously replaced (1969) discriminator electrolytic and decided to test the valves. I now know why the EF91 became obsolete: 1x heater cathode leakage and 2x low emissions then from my spares, 1x gone to air and 1x low emissions. The EF80 showed excellent emissions.

It probably needs IF re-alignment now but I will give it a go as is.
PJL is offline  
Old 6th Sep 2019, 10:18 pm   #31
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Jason FM Tuner

I realigned the IF the next day and it was way out. It is far more sensitive than any tabletop and most 'tuners' of that period and usefully covers 85-105MHz maybe because the design pre-dated the BBC frequency allocations or perhaps to sell in mainland Europe?
PJL is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:48 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.