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Blog posts tagged with 'MULLARD'

ZONE REFINING OF GERMANIUM FOR YOUR OC71 etc.

A pal of mine, knowing I am a chemist decided to bring me this photograph from his time at Mullard Semiconductors - he thought the Dreschel bottles in the background would float my boat but in actuality it's the process being undertaken that piqued my interest.  My pal told me that this was an Orgone Accumulator - silly boy - but we know different!!

What we have here is a photograph taken in 1955 at the Mullard semiconductor materials laboratory with a Process Engineer purifying an ingot of Germanium for semiconductor manufacturing by a process known as Zone Refining, an elegant method which depends on  the concentration of impurity solutes in the liquid phase due to a low partition coefficient.  

And here's how it works: -

A germanium ingot is placed in graphite container called a boat which in turn is placed inside a silica tube under an argon or nitrogen atmosphere.  A molten zone is created in the ingot by passing it through an RF heated zone which raises a portion of the ingot to 932oC which melted the germanium and as the solubility of any impurities is higher in the liquid than the solid phase, the impurities tend to concentrate in the molten zone which gradually moves down the ingot, taking the majority of the impurities with it until they are eventually concentrated at one end of the ingot.  

The impure end is 'lopped off' and the process successively repeated until a 99.995% pure germanium ingot remains.   The process was quite slow with transit of the ingot progressing at 1cm/hour so purification could take some time.  This photograph was taken only 5 years after this process was originally invented by Dr. W Phann at Bell Laboratories in the 'States.  The process is still in use today with silicon for chip wafers being refined in the same way, however, the process has been refined (sic) over the years to be much faster as a continuous process with new material being added as the impure bit is removed rather than the slower batch process you see here.

Interestingly enough, a similar process known as Zone Remelting was used to put impurities back in to the germanium ingot with a high degree of homogeneity to 'dope' it with antimony and/or arsenic to inbue negative, n-type semiconduction or conversely aluminium and/or boron to imbue positive, p-type semiconduction.

 

GLAMOUR OR SID - WHICH ONE FOR THE 1955 MULLARD CALENDAR

As early as 1952, Mullard top brass were considering how best to promote their product range with the expounding of an idea which became all too prominent some 10 - 15 years later.      The idea was of course a calendar and not just any calendar but a glamour calendar, much board room discussion was made of the merits of Roedean-esqe girls showing cheeky smiles, a shapely ankle or even a svelte swimsuit with a plunging back line but the eventual conclusion was that such an approach might sully the wholesome Mullard image - the phrase 'sex sells' wasn't yet coined by Madison Avenue though I am sure Don Draper and Roger Sterling must have thought of it!!!!!!

Instead, a compromise was reached, the calendar format was used with a rather fetching presentation of Sid the Serviceman on the front cover and handy valve equivalents and operating data inside for common valve types.  Here we see the Mullard Top Brass at the Mullard Dealer event in 1954 perusing an advance copy of the wall chart with the chap on the right, Mr D M Hall, Manager of the Mullard Valve Sales Department appreciatively commenting, sotto voce, "I say, phwoarrr, look at the getter bloom on that!"

Today, these wall charts do occasionally turn up with their page edges crinkled and worn, a testimony to their use as an aide-memoir in some long gone radio service workshop.

MULLARD AUDIO VALVES ON TOUR IN 1954

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: -

1954 AND A BIG EHT CHANGE FOR MULLARD PICTURE TUBES

The march of time and progresss marched inexorably on at Mullard's and an interesting development occurred for CRT in 1954.  If you look at some of my earlier blog postings on the manufacture of CRT, you will see that the EHT connections provided pre-54 were somewhat different to those you may be more familiar with but this did indeed change in 1954.

If you recall, the earlier EHT connection comprised of a number of wires fused into the side of the envelope which was in turn soldered to a metal cap on the tube's exterior wall.  To make such connectons required a fair deal of skill and the whole operation was labour intensive with Mullard suffering a trying time during 1952 when quite a number of these connections failed due to rough handling in transit which was expensive and wasteful - especially as the packaging for these early CRT was very good as well.

Anyhow, the replacement connector was a one piece jobbie made of a nickel-chrome-iron alloy which you can see in the photo below: - 

And here is a photo showing the corresponding EHT connector - are things looking familiar now?: -

Item D was a handy little adaptor comprising of a thimble cap of standard dimensions, the lower end of which was fitted with six spring prongs to locate the terminal.  This adaptor allowed TV receivers from past years to be rejuvenated with one of the newer tubes without changing the existing wiring - those chappies at Mullard thought of everything you know.

 

NEW FOR 1954, MULLARD GERMANIUM CRYSTAL DIODES

Don't you just love the parlance "crystal diode".  1954 was the year that Mullard took their first steps into the mass market with semiconductors.  Trumpetting their new  product as having low shunt capacities and higher rectification efficiency than those old fashioned valve things, the range started with two devices specially developed for television use.  

There were teething problems as the TV trade tended to attach these new fangled devices into TV circuits using a poker heated in t'fire thence cooking these early and not particularly robiut devices but application of tweezer heatsinks thoughfully provided by an arrangement between Mulard and Antex to solve this unforseen setback.

Type OA61 was designed as a video signal detector with it's handy PIV of 30V.

Type OA61 was designed as a DC restorative and synchronising pulse clipper with a PIV of 100V.

Both types demonstrated a minimal shunt capacitance of 0.1uF and a working temperature range of -50 - +60oC.  The future had arrived!

THE EL84 OUTPUT VALVE MULARD'S MINIATURE MARVEL!

You can read more about this Noval based output pentode on one of my valve product pages but here, today we have an excerpt from a Mullard 1954 press release extolling the vital statistics of this versatile and today much loved device: - 

 

 

 

USE MULLARD TO KEEP VOLTAGES STEADY, EDDY!

We have had a run on stabiliser devices recently, so I thought it was perhaps time to write a blog article about how these work.   Interestingly, they are not a valve in the true sense as they do not amplify but ratherfind use in maintaining steady DC voltages in power supplies where mains supply variations occur or within circuits where a reliable reference voltage is required for operation.

The simplest form of voltage stabiliser consists of a rod anode surrounded by a cylindrical cathode which are mounted within a glass bulb which has an atmosphere containing a single or multiple low pressure noble gas mixture with neon, helium or argon commonly being used - more on this later..  As a DC potential flows, the cathode will strike with a visible glow and a burning voltage flows from anode to cathode.  This potential has the useful property of only minimally being varied by changes in current as you can see in the following picture: -


 

The voltage at which a stabiliser strikes and burns at is determined by the gas or gas mixture used within the envelope with the supply voltage typically being higher than the operating voltage required to ensure strike and burn occurs.  Mullard made a variety of these devices, the parameters for which are listed below: -

This phenomenon has two effects - if the input voltage changes, then the burning current, I, and resistance, R,  will also change BUT the voltage across the stabiliser will remain constant.  The only deviation that can occur is when the ratings of the stabiliser are exceeded at which point, the stabiliser will rapidly fail - if one were to perchance reverse the anode and cathode connections then again, the stabiliser would (spectacularly & rapidly) fail.

So, there we have it, a quick treatise on these fascinating devices, Made by Mullard amongst others but remember, they are not a valve!!!

 

THE DELIGHTS OF MULLARD BIG SCREEN TELEVISION IN THE 1950S

 

Now this really was quite the thing.  In the 1950's the availability of Lay-zee-boy chairs in the UK was but a wistful dream but they had big screen TV you know.  Today's Mullard archive photo shows the demonstration of range of six Mullard forward projection televisions of varying screen sizes up to a  maximum of 4 ft x 3 ft.  The official report states that viewers were wowed by the clarity and quality of the picture which was maintained despite relatively high ambient light conditions, no comment seems to have been recorded about the perceived comfort of the dining chair seating.

THE WONDERFUL ECC83!

You can read more about this Noval based twin triode on one of my valve product pages but here, today we have an excerpt from a Mullard 1954 press release extolling the vital statistics of this versatile and today revered device: - 

 

VALVE TESTING AT MULLARD'S SERVICE DEPARTMENT

Valves were from time to time, returned to either the main Mullard service department or one of the regional service centres.   Reasons for return were varied and included,   defective new product and devices that had failed during their guaranteed life. Today's blog entry will describe what happened to these naughty devices when received at the service centre.

On receipt, the suspect device would be unpacked and listed in a return register attached to a numbered report form on which the results of any tests carried out would be recorded.  At this point, the report contained details of the valve type, manufacturers coding, parcel condition on receipt and result of a subjective visual inspection of the valve.

The device and report would then be passed to a service bench where a range of static tests would  have been made using a test board.  These tests were carried out in a definitive sequence and should a test device fail at any point, the sequence was discontinued.  The test schedule comprised of the following tests: -

The first static test was always a filament check where both continuity and filament current draw were checked.  

The second test was for insulation resistance where the cathode was energised to a positive potential and measurements of leakage current to other electrodes was measured whilst gently tapping the envelope with a rubber hammer to reveal possible intermittent faults.  

The third test was a vacuum test where the valve under normal operating conditions was connected to a microammeter in series with the grid to measure any reverse grid current and hence check for a 'soft' valve.  

The fourth test was an estimation of cathode emission where the valve was effectively configured as a diode to form a composite anode with an AC supply being applied to the anode and the total rectifed current hence being measured and compared to specification.  

The fifth and final static test was a check of the anode current-grid volts characteristic curve  at several different grid voltages.

If all static tests passed specification then the test device would be passed to another test area and operated for a period of 15 minutes in a suitable receiver - typically a Mullard or Philips receiver.  This allowed a direct practical check of device behaviour in an actual circuit and additionally allowed a subjective assessment of any noise and microphony.

If necessary, the final test stage would involve valve disssasembly for further visual and microscopic examination, the results of which were recorded on the test report.

At the conclusion of testing, the report would be submitted to a claims department who decided, based on report contents whether or not the valve could be replaced under the terms of the guarantee 

Today's photo presented below shows Doreen Snailpen operating a valve test board at the Mullard Waddon Service Department:-