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Blog posts tagged with 'mhsvt'

WE'VE GOT 17 MULLARD VALVE TESTERS AT THE BBC

 

Today's dip into the Mullard factory archives has come up with this photo of a suited gentleman testing valves using a Mullard High Speed Valve Tester (MHSVT).   How many people wear a suit whilst valve testing  - I wear a string vest and a lime green thong whilst testing our wares -  however, I digress.  The formal attire should give a clue for this is the MHSVT in the main transmitting room at BBC Alexandra Palace some time in 1953.  

I think this photograph was taken during valve maintenence testing undertaken immediately prior to filming an episode of Jigsaw  where a young art student from Perth, Australia, got an audition drawing cartoons  - "Can you tell what it is yet, little girl.........?." said the art student.   "Is that an 813 in your pocket or just a small digeridoo?"  innocently trilled the pigtailled young lady.  

Altogether, the BBC had 17 of these instruments, indeed, the fourth one off the production line of the first production run was bought by the BBC for use at Lime Grove studios where it was used for peridoic testing of a stock of 12000 valves.

SISTERS DOING IT FOR THEMSELVES AND KEEPING IT IN THE FAMILY

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............................

 

 

 

I SAY, BASE ADAPTORS FOR YOUR VALVE TESTER - SIMPLY SPIFFING!

 

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)

NEW FOR 1954 - FACILITIES FOR THE MULLARD HIGH SPEED VALVE TESTER

As careless consumers were forever popping the HT fuse due to sputtering rectifiers and valve overloads, Mullard hit upon the idea of introducing an HT Overload cutout for all 1954 production models of the MHSVT.   It was based on a polarised relay which would trip at overload condition but could be reset at the press of a button.  The cut out trip current was 200mA.

Another handy wheeze was what Mullard termed "the MHSVT pre-heat device" where a toggle switch was added which allowed the instrument circuitry valves to have heaters lit without a valve setting card inserted and the gate handle in the "Off" position.  To avoid CRT wear, no EHT - just LT was applied.  On inserting a card and valve, the CRT indicating spot appeared virtually instantaneously which was considered a boon for the busy commercial workshop.

These enhancements could be retrofitted to earlier instruments on their return for routine overhaul - Mullard were very specific in that kits of parts could not be sent to users for self installation.

The cost of upgrade was as follows: - 

Pre heat device: £2 10/-

Overload cut-out: £2

Both pre-heat & cutout: £4

The diagram below shows the circuit amendments that were made - does your MHSVT have them?:-

 

 

MULLARD AT EARLS COURT RADIO SHOW 1953

How times change, these days, event stands are put up by gum chewing muscle bound chaps wearing Dickies work pants and steel toe capped boots, however, in 1953 as you see here, the Mullard stand at that years radio show was erected in all it's glitzy splendour by chaps in suits and ties - stirring stuff!

 

 

In 1953, Mullard had two locations at this venue.  First there was Stand 91 which boasted information centres for listeners and viewers as well as a comfortable lounge where commercial and technical problems affecting valves and cathode ray tubes could have been discussed with eager Mullard representatives.  In addition there was also Demonstration room D7 which was devoted to trade demonstrations of the MHSVT and the Expandabox system - more on this development and a hilarious story as well in a future blog!

1953 BRINGS NEW ACCOUTREMENTS FOR THE MULLARD HIGH SPEED VALVE TESTER

If you felt that a trolley fulfills three important requirements - i) to serve as an attractive self-contained counter; ii) to serve as a compact storage facility; iii) to serve as a mobile platform then you can understand why Mullards commissioned Domain Products of Barnby Street, London to manufacture a purpose built trolley to store your MHSVT on.        This might look like a hospital trolley but it differed in that it could be easily dismantled Ikea style by the removal of eight clamp bolts and it had two hooks on the back legs of the trolley for winding the mains cable on - pretty good huh - and all for £6 15s. 

 

And that's not all as you could also buy card containers to store over 1000 valve test cards.   Having four compartments and a handy lid to store valves under test these were a snip at 35/- each and fitted beautifully onto the trolley.

 

A COVER FOR YOUR MULLARD HIGH SPEED VALVE TESTER

In March 1952, if you wanted to spruce up your service department, you could buy a smart, dustproof, tailor-made cover in strong silverised leathercloth for your MHSVT.   It had red piping accents and was only 13/-.

Here we see Hortense Balchin who stated that 'My Wilbert always said that a workman must care for his tools and they will go on to care for him." and she went on to demonstrate how clean this cover kept her Wilbert's instrument : -

WHAT CAN THE MULLARD HIGH SPEED VALVE TESTER DO

Today, I have had an e-mail from Veaceslav in Moldova, asking what tests the MHSVT can do.   This valve tester can do seven main tests sequentially and these are: - 

Test 1: check heater filament continuity.

Test 2: check insulation between electrodes - cold.

Test 3: check heater - cathode insulation.

Test 4: check insulation between electrodes - hot.

Test 5: check reverse grid current is acceptable.

Test 6: measures emission indicating 'goodness' on a CRT screen.

Test 7: checks correct connection of each electrode to each valve pin.

Parameters for each test are set using the test card for a particular valve which is slotted into the rear of the tester.

A useful tester but for me, I prefer the AVO VCM series and this is what we use at Mullard Magic HQ.

 

SOMEWHERE TO KEEP YOUR MULLARD HIGH SPEED VALVE TESTER CARDS

In early 1951, Mullard introduced a handy steel container finished in 'Dimenso' - that's posh for silver hammer finish paint. The container was designed to hold 600 cards in six separate compartments.   This number of cards would test 750 different valve types.    The container featured rubber feet and was sized to be equivalent in length to the depth of a tester so it could sit alongside - provided enough room was left to allow the clamshell top to open!   And the price for this marvel of modern engineering in March 1951 was 45s - a snip!

EXOTIC COMPONENTRY IN THE MULLARD HIGH SPEED VALVE TESTER

At the time of introduction, two 'hollow state' devices the MHSVT contained were considered exotic.   The first, the 85A1 voltage regulator is a neon filled reference two electrode device which serves to provide the MHSVT with it's reference voltage stable in normal useage to 0.17% variance and over it's entire life. stable to within 0.5% of nominal value.     The second is the DG7/5 cathode ray tube which is an electrostatic medium persistance tube .    What is interesting is that this CRT is used in this application purely as a voltage indicator, measuring various currents by means of voltage drops across resistances brought into circuit by the punched card valve selectors.  No need for a timebase here you see.  

With the passage of 60 years or so, opinions change and now we consider a CRT and a neon regulator rather passe and instead become animated if not rather excited by the EL37 beam tetrode that a MHSVT also contains - more on this desirable audio valve in a future blog entry.