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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Jan 2020, 3:53 pm   #41
Maarten
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Default Re: Nude EF50's Look Great

Sylvania is from the USA.
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Old 2nd Jan 2020, 4:02 pm   #42
julie_m
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Default Re: Nude EF50's Look Great

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Originally Posted by llama View Post
And what company/country/province is "Sylvania"?
Graham
Sylvania were a manufacturer of light bulbs and radio valves.

"Sylvan" is an adjective, derived from Latin, and meaning related to woodland.

Transylvania literally means a place on the other side of the forest.

Sylvanian Families were a range of collectable animal figures, with a matching range of houses, furniture and vehicles to ensure that there was always something else for a parent to buy .....
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Old 2nd Jan 2020, 4:49 pm   #43
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Default Re: Nude EF50's Look Great

One of my main interests is in WW2 airborne radar, H2S in particular, which of course used VR91/EF50's in quantity. In one of the documents I have there is an observation that Mullard EF50's are causing problems in certain locations in the H2S system, and Sylvania examples should be used instead as their quality is better.
I'll try and find the exact reference.

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Old 2nd Jan 2020, 5:45 pm   #44
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Default Re: Nude EF50's Look Great

Sylvania are still very much around - though they've moved on from making EF50s and now do a good line in decently-low-RF-hash-generating GU10 LED 'bulbs'!
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Old 2nd Jan 2020, 6:53 pm   #45
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Default Re: Nude EF50's Look Great

These classic valves are revealed as very futuristic looking [without the "can"] by Mike in post 1*.
Quite unexpected! As Andy said [post 6*] "nude" tends to engage the brain. It's genetic you know, although conflating that word with "spanking", in the initial post, could be asking for trouble
Perhaps it's just me?

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Old 2nd Jan 2020, 8:39 pm   #46
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Default Re: Nude EF50's Look Great

As a consenting adult, the matter can probably be considered closed in this instance.
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Old 2nd Jan 2020, 10:55 pm   #47
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Default Re: Nude EF50's Look Great

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Originally Posted by turretslug View Post
Apparently, there were even a handful of mid '40s consumer radios that used the EF50 as an RF stage;

http://www.bushradio.co.uk/bushexport.html

which seems a little odd- something like the EF39 would seem more appropriate from various angles- variable-mu as opposed to straight, the same International Octal valve socket as other valves on the same chassis, easing stock-holding and chassis-punching. Perhaps by this time EF50s were so plentiful as surplus that there was an element of "too cheap to resist" by some designers. Marconi's CR150 used a quad of EF50s in its front end with scaled AGC for the two RF amps, but that's understandable in a set that endeavoured to cover up to 60MHz, less easy to rationalise in a domestic-quality set with coverage to 22MHz or so.
Possibly the EF50 was chosen for lower noise at upper HF. This application was covered by Moxon (1) under the heading “Improvements in shortwave reception” (as applicable to domestic broadcast receivers). He said: “It is usual, therefore, in the better class of receiver, to precede the frequency changer with an r.f. stage. For lowest noise factor this should be one of the high-slope pentodes such as the EF54, EF50 or SP41, and such receivers first made their appearance on the market a year or two before the outbreak of war.” He then went on two describe a simple but effective tuned image reduction circuit which had the side effect of reducing the RF stage gain, about which the comment was made: “The gain reduction means that to achieve adequate gain at the higher frequency s.w. broadcast bands, the r.f. stage must employ a high-slope valve, but as previously explained this is also desirable from considerations of noise factor.”

The Murphy TA160 of 1951 used this kind of image-reduction circuit, and had 6F1 high-slope pentode RF amplifier. Other British domestic receivers of the period to use high-slope pentode RF amplifiers were the Ambassador Viscount, with the EF80 and the Armstrong EXP119 and BS125 (early version), with the 6F13. I think that there may have been some other late 1940s domestic receivers that used the EF50, perhaps the Ace 600 and Strad 491E, but I am not sure.

In its 1950s point-to-point HF communications receivers, Marconi typically used two RF stages, with a Z77 high-slope 1st stage and a W77 remote cutoff 2nd stage. It looks as if it saw the Z77 as the successor to the EF50 for that application.

Moxon mentioned the SP41 high-slope pentode, which I think was the 4-volt heater counterpart to the SP61. The latter, of course, was the valve nominated by Baxandall for use in his fairly well-known 1950 (published in 1952) tone control. He commented that a high-slope pentode was required for best results, although other valves could be used for less critical applications, with an EF37A recommended where input signal levels were below about one volt - presumably that spoke to the higher microphony typical of high-slope pentodes. But Baxandall’s use of the SP61 does provide a very credible case for the selective use of high-slope pentodes in AF applications.


Cheers,


(1) L.A. Moxon; Recent Advances in Radio Receivers; Cambridge University Press; 1949.
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Old 2nd Jan 2020, 11:54 pm   #48
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Default Re: Nude EF50's Look Great

It's been suggested that if the city of Cambridge had been closer to London and had enjoyed a better TV signal, the EF50 might never have been developed and Britain's WW2 radar wouldn't have been so successful.

In the late 1930s, Pye of Cambridge were a successful TV manufacturer, but ironically the Alexandra Palace signal barely reached Cambridge: its range for reliable reception was some 25 miles and Cambridge was almost 50 miles distant. C O Stanley, owner of Pye, was determined to market a set of high sensitivity that would give reliable reception of Alexandra Palace in Cambridge. Back in those days, that required a multi-stage TRF tuned to 45Mhz (presumably with excellent screening between valves). Pye engineers specified the EF50 and the Pye valve company, Cathodeon, had a go at making it but failed. Fortunately, Pye also had relationships with Mullard and Philips. Mullard struggled with the innovation in the EF50 and in the end it was Philips in Einhoven who succeeded in manufacturing the valve.

So Pye ended up with the most sensitive TV receiver in 1939, just as war broke out and Alexandra Palace ceased to transmit. Timing could have been better. However, that high gain TRF TV receiver chassis turned out to be an ideal IF strip for the all-important radar systems then under development. The technology transfer idea was facilitated by a familiar radio name: Edward Appleton, then of St John's College. So it was that a valve born of the poor TV signal in Cambridge could claim to have helped win WW2.

The Eindhoven production was of course short-lived after the Nazi invasion of the Netherlands and, in a series of events worthy of a James Bond movie, the EF50 manufacturing data, tooling and thousands of the unique glass bases were transferred from Holland to the UK to allow manufacture to continue (by Mullard, M-OV & Cossor), and to the USA (Sylvania) and Canada (Rogers).

So whether an EF50 is red or silver might just give a clue as to its manufacturer, but then again it might not.

Martin
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Old 3rd Jan 2020, 1:12 pm   #49
Maarten
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Default Re: Nude EF50's Look Great

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Originally Posted by G6Tanuki View Post
Sylvania are still very much around - though they've moved on from making EF50s and now do a good line in decently-low-RF-hash-generating GU10 LED 'bulbs'!
Sylvania was split up. Philips bought their consumer electronics division and I think their components division (Sylvania ECG anyway) together with the Philco brand name. Their lighting division (or RF-hash-generator division) is part of Osram.
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Old 4th Jan 2020, 5:41 pm   #50
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Default Re: Nude EF50's Look Great

The BBC used the EF50 in their AMC/3 microphone amplifier.
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Old 4th Jan 2020, 8:10 pm   #51
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Default Re: Nude EF50's Look Great

Interesting place to find a valve considered to be somewhat microphonic. I wonder if they had anti-vibration mountings?

The rest of the circuit used CV138 (EF91) throughout, so the EF50 was in there for a special reason. I wonder if it happens to have better than average noise behaviour for a pentode at the particular source impedance it is presented with? Shunt feedback as well.

David
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Old 4th Jan 2020, 10:53 pm   #52
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Default Re: Nude EF50's Look Great

In the description of the potable acoustic measuring unit is included the comment:

“At the time when the amplifier was designed, miniature valves having a sufficiently low level of hum and microphony for first stage operation were not available. As a compromise, however, selected specimens of the EF50 are used.”

From that one could reasonably infer that the better EF50 samples (along the desired low-hum, low-microphony vector) were better than the better EF91 (CV138) samples. One could wonder why not the EF40, which was in the initial Rimlock range and so might have been available when the unit was designed, although Mullard may have been slow to start UK production of some of the early Rimlocks, perhaps concentrating on the core radio types.

Later in the description it was noted that the input transformer and valve, etc, were on a rubber-mounted sub-chassis. There is more detail about rubber mounting and its isolation benefits in the description of the AMC/3.


Cheers,
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Old 4th Jan 2020, 11:45 pm   #53
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Default Re: Nude EF50's Look Great

Quote:
Originally Posted by Radio Wrangler View Post
Interesting place to find a valve considered to be somewhat microphonic. I wonder if they had anti-vibration mountings?


David
Interesting to note from the text though (attached), the EF50 was thought to be a compromise for the application. And that they had to hunt through some to find the better ones.
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Old 5th Jan 2020, 9:02 am   #54
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Default Re: Nude EF50's Look Great

I think the EF40 was not available at the time but the EF37A was and given that an EF50 is not exactly miniature you might think it woud have been a more obvious choice.

The microphony problem was probably not serious since the unit would be in an equipment rack some way from loudspeakers or other dissruptive noise.
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Old 5th Jan 2020, 5:38 pm   #55
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Default Re: Nude EF50's Look Great

By coincidence I have been browsing some old radio books and found the 'all EF50 TRF' article in the July 1947 Short Wave Mag. by G5UM It's on the US history of radio site as well. there is also a follow-up article in the August issue about neon stabilisers. I might have a go at this as I have the inevitable big box of these bottles under the bench, plus plenty of other bits as well.
I should be able to fit it onto a mess tin as a chassis.
Mike, G3ZII.
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