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RASPBERRY RIPPLE AND PIE OR AC RIPPLE AND PI - YOUR CHOICE - Thursday, April 03, 2014

Today, I thought we would talk about AC ripple and Pi section power supplies for as we all know, one of the most important considerations in an amplifier is the minimisation of AC ripple that can be superimposed on the DC voltage supplied by a rectifier.

The value of ripple is dependant for a unit voltage on the reservoir capacitance and the smoothing network - let's take a typical Pi network comprising of C1, a reservoir capacitor, and C2, a smoothing capactor with either an inductance L or a resistance R: - 

The ripple voltage is inversely proportional to the values of C1 and C2 - so if you want low ripple then get BIG capacitors.  Some people economise in the design of equipment by substituting a resistance in place of a more expensive choke with little appreciable rise in perceived ripple current.  Of course in this world 'tha gets nowt for nowt,' and the resistance unfortunately reduces the DC output voltage dependant upon current delivery loading and resistance value.   This disadvantage can be minimised by feeding the PA stage output valves from C1 rather than C2 with the ripple being nullified by a push-pull output stage, particularly if this stage is balanced.

Taking the above example: -

For C1 = 8 uF; C2 = 16 uF; L = 10 H then Irip = 210 mV for V0 = 251 V @ C2

For C1 = 50 uF; C2 = 50 uF; R = 500 Ω then Irip = 210 mV for V0 = 221 V @ C2 or 265V @ C1

So there you have it but my take on it is don't be cheap, use a choke and preferably one bought from Mullard Magic!!!!!!

 

 

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SISTERS DOING IT FOR THEMSELVES AND KEEPING IT IN THE FAMILY - Monday, March 24, 2014

 Today's blog entry shows a press photograph and article from the Wandsworth Beagle newsheet from 1954 and was taken at the Mullard Equipment Factory at Wandsworth.

It shows Betty Calf, Hetty Calf and Lettie Calf assembling Mullard High Speed Valve Testers - truly a family affair - and not a tin of pineapple rings to be seen!  I wonder if anyone will 'get' that last comment - answers on a postcard............................

 

 

 

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MULLARD HIGH QUALITY TEN WATT AMPLIFIER THE 5-10 - Monday, March 10, 2014

'Technical advances have effected considerable increases in the quality of broadcast and recorded sound with television sound and FM transmissions including the full range of audio frequencies.  It is thus essential to have an amplifier which does full justice to a high quality audio signal.  Details of such a new amplifier have been released by Mullard in the booklet "Mullard 5 Valve 10 Watt  High Quality Amplifier Circuit (ref. no. MV8104).'

The above entry is from a press release by Mullard dated October 1954.  Today, the 5-10 is much revered  and not at all in the shadow of it's larger brother, the 5-20 - and so it should not be when it boasted an output of 10W showing a THD of < 0.4% with hum and noise being inaudiable being -74dB below maximal output.  All this and a flat frequency response to within +/- 0.5dB within the range 10 - 20000Hz to boot!

Of course, this amplifier was designed to showcase a range of Mullard valves, first, the first stage voltage amplifier used the low hum/low microphony EF86 pentode which was in turn coupled to a cathode coupled phase splitter, courtesy of an ECC83 dual triode.  An elegant design point was the g'' of the ECC83 being capacitively earthed with the bias for the second section being applied due to current flowing through a common cathode resistor - a nice touch that prevented motorboating or any form of instability at normal driving conditions.  

Interestingly, the output stage was configurable with an 8K or 6K secondary to adjust loading such that high power or lower power with a consequently better transient response could be enjoyed.

The powerhouse for all this was supplied by a GZ30 rectifier or if you wished to stay with an all B9A arrangement then alternatively, the EZ80.   THe PSU was of a resistance-capacitance design utilising a comparatively large reservoir capacitance of 50uF to reduce ripple current.

And here is Mullard Laboratories photograph of "one they built earlier." : -

 

 

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THE MIGHTY ROHDE & SCHWARZ EK-07 - Monday, February 24, 2014

 Well, evidence of my advancing years crept up on me and was revealed today when I ran out of puff trying to move my Rohde & Schwarz EK-07 receiver.  Widely acclaimed by some as the best valve communications receiver made, I am priveledged to have one courtesy of my friend Norman Varnes (G4YXX) who tells a tale of spirited bidding over a glass or several of jenever at the famed Helmut SInger emporium to liberate it with a terrible sacrifice not only in pounds sterling but also a most horrendous hangover courtesy of much falling down water consumption during the lengthy negotiations necessary to secure this leviathon. 

For those that are not 'in the know', here's a little history lesson.......  The year is 1957. Rohde & Schwarz, founded in 1933, introduced the EK 07 shortwave receiver. This milestone set the benchmark for precision engineering in the radiocommunications market. Frequencies could be read with high accuracy, image frequencies were a thing of the past, the radio was immune to overload, and sound quality was above average. This was reason enough for the German Armed Forces to adopt the EK 07 as its standard communications intelligence receiver beginning in 1962.

Indeed, my EK-07 has an interesting provenence as it came from the renowned Norddeich DAN German maritime radio station and did sterling service until being demobbed on station closure in 1998.  Here is a nice photo of a bank of EK-07 in action at DAN: -

 

And here is an even nicer photo of the EK-07 production line at R + S in 1961: - 


Finally, here is my baby - a true representation of a boatanchor weighing in at 75kg: -

 

Thanks are also due to my friend Brian Harrison (KN4R) who has helped me out with an English translation of the weighty EK-07 manual so I now have no excuse to not check this over to ensure all is in spec for the next 50 years of operation - time to get weaving!!

 

 

 

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I SAY, BASE ADAPTORS FOR YOUR VALVE TESTER - SIMPLY SPIFFING! - Sunday, February 16, 2014

 

May 1854 brought a useful accessory addition to the Mullard High Speed Valve Tester (MHSVT).  Developed in conjunction with Messrs. Spear Engineering of Warlingham the range comprised of eight adaptors to facilitate the testing of valves for which no existing valve base was provided on the instrument.

These were precision items, with the bodies of the adaptors being trned from duralumin - usually reserved for aircraft bodies - and just look at the adaptor below for testing the EY51 boost diode - impressive huh?

The adaptors were engraved 1-8 with the figures clearly identifying each adaptor body and were priced at £4. 2. 6d. (£4.125)  the set complete in a holding rack.   otherwise the adaptors were available idividually at prices ranging from 7s. 6d (37.5p) to 15s. 0d. (75p)

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MULLARD AUDIO VALVES ON TOUR IN 1954 - Sunday, February 02, 2014

Today's photograph from the annals and archives of Mullard is a press photogaph from early 1954 where Mullard representatives chatted animatedly with Mr A J Walker Hon. Secretary of the Association of Public Address Engineers at the Mullard Stand during the APAE exhibition.  It was recorded that Mr Walker was very excited by the possibilities that the EL84 presented to the world of PA: -

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BATTLE OF THE BULGE - THAT WW2 FILM WITH ALL YANK TANKS! - Saturday, January 25, 2014

Just watched this film after many years and I do know that many people have mentioned the use by Colonel Hessler of a Hallicrafters SX28 in his command caravan - nice to see such a pretty Allied receiver being used as a transmitter by a Wermacht tank commander!!  However, no-one seems to have ever commented on the fact that both sides appear to use Shure T-17 microphones.

Even more horrendous is the Telly Savalas character driving around in a tank with most of the mantle, turret and gun 'shot away' whilst two R1555 have miraculously survived after having been stolen by the Yank tankers from a passing Lancaster bomber.   Actually, I use the term survived in the loosest terms as both receivers appear to have been modified quite comprehesively and here is the photographic record to prove it, enjoy!: -

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TOOLMAKERS AT MULLARD & TV BAND III IN 1954 - Tuesday, January 21, 2014

When Band III TV was introduced in Britain early in 1954, Mullard heralded in the new age by having a range of valves available for the new receivers some two weeks after the British Government's TV policy had been confirmed in the House of Commons.

Here, we see Timothy Bustard, a Toolmaker at Mullard's Mitcham factory hand finishing a new anode making tool for the PCF80 triode-pentode valve which acted as a frequency changer for Band III TV transmissions. The tool is used in a press where nickel sheet is fed into the press and seven successive operations of punching cutting and bending using the multi stage tool pictured resulted in a  finished anode being produced.

Here you see Timothy using a strip of nickel sheet as a guide before final fine grinding of the radii within the tool cavities.

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COMMUNICATION EQUIPMENT KILLERS - Thursday, December 26, 2013

Now here's a Christmas thought, someone once jokingly said that during the 1950s and the 1960s every radio amateur licence came with a free Maxi-Q chassis punch and chisel set with which classic surplus radio equipment could be disfigured and systematically badged and ruined.       Having recently purchased a WS22 set that has had such treatment I can ruefully agree.

Those like minded individuals amongst you should therefore appreciate the following cartoon: -

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WHY IS MY TORCH BULB CALLED LES & NOT TYLER OR CHARDONNET? - Sunday, December 15, 2013

Had a query today from Finland about small Edison Screw bulbs, so, I thought I would supply interested parties with a listing of all ES bulb sizes so now you know why a bulb's name is MES or LES instead of DAVE or TYLER - Katie Hopkins, I love her, don't you - wonder what she would make of the Mullard Magic mug?

 

 

Designation Base diameter (thread external) Name IEC 60061-1 standard sheet
E5 5 mm Lilliput Edison Screw (LES) 7004-25
E10 10 mm Miniature Edison Screw (MES) 7004-22
E11 11 mm Mini-Candelabra Edison Screw (mini-can) (7004-6-1)
E12 12 mm Candelabra Edison Screw (CES) 7004-28
E14 14 mm Small Edison Screw (SES) 7004-23
E17 17 mm Intermediate Edison Screw (IES) 7004-26
E26 26 mm [Medium] (one-inch) Edison Screw (ES or MES) 7004-21A-2
E27 27 mm [Medium] Edison Screw (ES) 7004-21
E29 29 mm [Admedium] Edison Screw (ES)  
E39 39 mm Single-contact (Mogul- in America) Goliath Edison Screw (GES) 7004-24-A1
E40 40 mm (Mogul) Goliath Edison Screw (GES) 7004-24

 

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