EF50 Question

[M0FYA Andy]

I have the Air Ministry note which says that Sylvania rather than Mullard EF50's were to be used in certain positions in H2S radar units, but I recall this was due to performance rather than life issues. Now where have I put it.......?

Andy

[Panrock]

Originally Posted by Heatercathodeshort

One of the earliest uses of the EF50 was the RF strip in the 1939 PYE 9C and 12C television receivers. I believe the very early versions had hooked pins. There was the secondary emission version the EE50 and the double version the EFF50. John.

And of course, the home-build post-war PT. Argus receiver was EF50-rich.

Steve

[Heatercathodeshort]

The higher performance 'selected' EF50 valves were marked on the top with two black bars. These commanded a higher price that encouraged post war government disposal shops to paint black lines on the top...The top stripe versions were used by PYE in the B18T versions in critical positions. John.
PS A genuine striped EF50 from the USA, probably SYLVANIA.

[G6Tanuki]

In times past I built a 'Luxembourg' receiver out of an old surplus radar chassis.

Two EF50 RF amps, an EF50 infinite impedance detector, an EF50 as the first audio stage and a 6V6 as audio output.

Denco 1.6MHz IF transformers with additional capacitance meant six signal frequency tuned circuits.



An EA50 diode fed from the anode of the infinite impedance detector provided AGC.

It worked rather well!!

[Maarten]

Originally Posted by Heatercathodeshort

The higher performance 'selected' EF50 valves were marked on the top with two black bars. These commanded a higher price that encouraged post war government disposal shops to paint black lines on the top...The top stripe versions were used by PYE in the B18T versions in critical positions. John.
PS A genuine striped EF50 from the USA, probably SYLVANIA.

Since it's branded "Mullard" are the usual codes present, probably stamped in the lower rim of the shield?

[Cruisin Marine]

Very interesting story indeed https://en.wikipedia.org/wiki/EF50

[VT FUSE]

Saw plenty of EF50's with the 2 bars painted on but ALL Sylvania valves were marked "Made in USA" and most ( if not all ) had the Air Ministry Crown mark.
Possibly tested and evaluated Mullard were allocated the bars along with them being added by less scrupulous sellers?

I fully concur that there was a missive stating that certain stages in equipment should be fitted with Sylvania production, there was a strong belief held by amateur users that the performance of Mullard EF50's dropped in service, my understanding being that this was when utilised in VHF usage and some of which was above 45 MHz. Post war, my uncle was experimenting when amateur licenses were re-allocated and he had "plenty" of RADAR experience both at Marconi, TRE and later RRE,
he was involved in prototype builds and airborne trials. I inherited lots of valves and parts when he died.
Mike

[Heatercathodeshort]

The British Made Mullard is the only one with a base code 1230 1G1.

The two USA have what I presume to be a date code C9G and J9G. I would guess that the date is 1949 as they were removed from a PYE B18T.

The last one I guess could be a Cossor or Osram. No date codes but the A could stand for Air Ministry/American?

It appears that most of the Mullard branded EF50s were in fact made in the USA. John.

[RichardGM]

Do they count as "bottles" if they're in tin cans?

[M0FYA Andy]

Originally Posted by RichardGM

Do they count as "bottles" if they're in tin cans?

There's a conventional glass envelope inside the can!

Andy

[M0FYA Andy]

Here's an interesting picture of two 'naked' EF50's in a W1160A wavemeter (not owned by me), The circuit describes them as 'modified'. Can anybody suggest why removing the cans should be required? I'm guessing something related to capacitance.

Andy

[wave solder]

There is a picture of the internal glass valve at the top of this page here and an excellent article about it too. https://www.dos4ever.com/EF50/EF50.html

[bc312]

The top stripe versions were used by PYE in the B18T versions in critical positions.

Well I didn't know that - thanks John. I have a B18T and counted eleven EF50's. A later development of the EF50 was the EF54, and my R1392 receiver has five of those. The EF54 was also used in early GPO coaxial line systems and I liberated the station stock when the station finally closed.

Mike

[Heatercathodeshort]

Originally Posted by wave solder

There is a picture of the internal glass valve at the top of this page here and an excellent article about it too. https://www.dos4ever.com/EF50/EF50.html

I have just seen this film about the EF50. Absolutely great! The link to the PYE D16T in the post war section is one I uploaded to Utube quite a few years ago. It was quite a surprise to see it! John.

[G6Tanuki]

Though most people will have acquainted themselves of the EF50 through the likes of the '45MHz IF strip' and old TVs, it also played a big role in WWII navigational-aids - in particular the "Gee" hyperbolic system [which was a triumphant combination of electronics and mathematics].

The airborne RF26/27 front-end units for Gee used the EF50 in its military "VR91" uniform for the RF stage and the mixer, with an EC52 triode as local-oscillator. In times-past I had one of these 'RF' units as a 70MHz-to-7MHz converter feeding into a Pye PCR receiver; there was a low-power 70MHz beacon transmitter located somewhere in Derbyshire [Buxton?] which I could reliably hear in South Shropshire on my RF-unit using only a quarter-wave of wire as an antenna.
Hooking it to the 'dipole-and-director' TV antenna [aimed at Sutton Coldfield] got a big signal improvement even though this antenna wasn't in any way resonant or directive in 70MHz.

Immediately following WWII Eddystone published a design/sold parts for a "VHF Converter" using the EF50's spiritual successor the EF54 as the RF amp, but sticking with an EF50 as the mixer and an EC52 as local-oscillator. Ahem.. where have we seen something a bit like that?? I feel that a lot of the design-zeitgeist was cribbed from the Gee RF-units....

See https://eddystoneusergroup.org.uk/Ed...LL%20PAGES.pdf


I've got a much-butchered-by-a-previous-owner RF27 unit in my attic along with several NOS Sylvania EF50s; part of me wants to get it down and replace the cropped coils and variable-capacitors-with-vanes-removed to see what it can do on 50 or 70MHz.

[Hartley118]

Local lore here in Cambridge suggests that in the 1930s Pye, planning to design and build a range of TV sets in Cambridge, were hindered by a pretty poor signal from Alexandra Palace. The eastern end of the Chiltern Hills was a serious signal attenuator.

Pye needed to design a sensitive 45MHz front end with a good noise figure, but existing valves were inadequate. So it was that they negotiated with their Philips colleagues in Eindhoven to produce an RF valve design of better performance than the existing range. The EF50 was the result, and it appeared in abundance in early Pye sets, which gained a reputation for good ‘fringe area’ performance.

When WW2 demanded high performance radar front ends and IF strips, the EF50 was the answer and provided the required performance in detecting enemy aircraft.

Some say that it was the EF50 that won the war - all because Cambridge suffered from poor TV reception.

Martin

[G6Tanuki]

Eindhoven seemed to waste quite a bit of time in the late-1930s going down the 'secondary emission' route which produced valves like the EE50

http://www.r-type.org/exhib/aaj0017.htm

http://www.r-type.org/articles/art-023.htm

and EFP60 - http://www.r-type.org/exhib/aai0191.htm - which were ultimately a dead-end and the EF50 was hastily developed to re-gain [pun intended] the lead.

In the US they'd been through the equally dead-end cycle of Acorn valves for 'UHF' but their TVs and RADARs depended a lot on the 6AC7/1852

http://www.r-type.org/exhib/aaa0053.htm

and 6AB7/1853 - http://www.r-type.org/exhib/abo0070.htm

both on octal bases!

http://www.r-type.org/addtext/add196.htm

[Synchrodyne]

Originally Posted by Leon Crampin

The use of this method of control in FM receivers is interesting. The EF89 was frequently arranged to have g3 connected to the ratio detector stabilising capacitor, giving a limiting action of about 35V as measured across the capacitor.

Has anyone ever seen any g3 characteristic curves for this control mode of the EF89?

I haven’t seen any g3 characteristic curves for the EF85 or EF89. For example, neither is covered here: https://www.radiomuseum.org/forum/du..._pentodes.html, or here: https://www.radiomuseum.org/forum/su...surements.html.

Apparently, Philips developed this technique in 1953, initially with the EF85. At least that is suggested here: https://www.radiomuseum.org/forum/gr...is_part_4.html, about half-way down.

One may reasonably ask why it did not publish any g3 curves for the EF85 (and later the EF89), given that g3 curves were published for the EF50.

One possibility is that the g3 characteristics were not well enough controlled to support a published set of curves. This lack of characteristic control for typical consumer equipment RF pentodes was apparent with the EAF42, whose original intention was to allow the pentode g3 to be used as an agc delay diode. Apparently the g3-as-diode characteristics varied too much for reliable use, so that the EBF80, with a separate agc delay diode, was developed as an improved successor. However, for the FM AGC case, g3 characteristic variability may have been less of an issue, given that it was in a feedback loop, and that the actual levelling out voltage of the ratio detector was probably not a critical number.

Anyway, it appears that Philips did not see the need to rework the EF85 to have more closely controlled g3 characteristics, or to issue a “selected” variant, with a different type number. Nor was that done for the following EF89, which would likely be used in the same role.

Thus, well-controlled g3 characteristics was one feature of the EF50 that was not carried over to its successors.


Cheers,