High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

By Dorian Stonehouse

With valuable technical input from electrical and

mechanical expert: 

Mr Bernard Garland (scientific GURU Garland)

THIS majestic machine was made for operators who did not always possess electronic skills.
The tester came with several boxfuls of early plastic punch cards (data cards). It was, in effect, an analogue computer.

The E7600 valve (tube) tester analogue computer is built like a tank!

The operator would look up the valve type first.

A corresponding number would then appear on a list, directing the operator to the right card.

The operator would then plug the valve to be tested into the appropriate socket – on top of the tester.

They would push the card⇓⇓ into a slot, containing a matrix of contacts, pull the big lever⇑⇑ (which clamped the card in position), and start the test routine

(See below: pictures of matrix made up of switches, and punch- card data information).

A Mullard punch card (data card), showing card No (left); Socket position on the tester (left); No. of cards for the valve under test (left);  the wafer switch position (right); push buttons to press (right) and type of valve (bottom right)

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

I bought my Mullard valve (tube) tester E7600 (with thousands of data cards) many years ago on a well known online auction site.

Valve sockets with location numbered (see diagram bottom left of picture)

Adjustments are carried out by neat controls situated behind a metal flap at the front

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

You know, if you’re prepared to take a bit of a gamble, it’s possible to get a bargain by buying or bidding for those wonderful things which are “for spare parts or not working”; as quite often, it’s possible, without too much hassle, to repair many items yourself.

Controls adjust the position and brightness of a green spot which is beamed on to a screen by the cathode ray tube (CRT)

So, I took the cover off and found that the tube base had come off the neck of the cathode ray tube⇓⇓ – the tube inside the tester which produces a green spot, giving the condition of the valve being tested.

Anyhow, I fixed the base back on the neck – and it worked!

A green spot appears on a screen, which shows the condition of the valve (tube) under test

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

I put everything back again, then studied the technical manual that came with it.

Before long I was able to test many types of valves.

Unfortunately, when it came to testing the pair of  valves I needed to test: an EF80 (video amplifier) and an EL84 audio valve (tube), there were no matching data cards in my set – Sod’s law!

Looking towards the front of the tester from the inside, showing the lovely old wafer selector switch, tube base with hefty old transformer on the right

There was only one way around this apparent impasse:  make my own pair of data cards for these valves (tubes).

For this labour of love, I again consulted the one and only – Mr Bernard Garland (Guru Garland), the gent who managed to set up a jig to create plastic cards for this machine.

Like a one arm bandit fruit machine, the lever and long arm pulls a metal panel at the back of the tester containing a matrix of selected sprung switches

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

The big lever (above) connects to a back plate, which is initially held out, allowing a punch card to be pushed down the gap. The plate is then forced towards a set of chosen contacts on the second inside matrix

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

B9A valve bases only (EF80):

Looking at the switch matrix from the back right-hand side, each horizontal line of switches, is assigned a letter:  from A (top) to M (bottom).

Looking from the same position (right to left), each vertical line of switches is assigned a number from 1 to 10⇓⇓.

How to make the perforated data punch cards

Plasticard is best

The best method of making these punch cards is use Plasticard, a card which is often used in craft work. 

I opted for black card, 0.5mm thickness. 

It is possible to employ a few methods of making your own cards: 

1) Use a pre-existing data card from the set of data cards that may have come with the Mullard valve (tube) tester as a template. Then cut out the plasticard to the dimensions of the template; place the template over your plasticard and drill at the precise location depending on the voltage parameters contained in the data sheet of your valve (tube).

2) Do the above, but construct a metal sheet template out of the pre-existing data card.  After completing this task, mark and drill holes in the metal sheet to cover all the holes corresponding to the location of the matrix switches.  This is covered below.

To make the plasticard data card, you will have to take the cover off the valve (tube) tester, and familiarise yourself with the tester.

Each punched hole on the test card will correspond to:

  • Pin location and function
  • Value of test voltage applied to each pin
  • Adjustment of spot on the cathode ray tube

Luckily, I have already mapped the connections for one example valve (tube). But the principle applies to all valves to be tested. 

It is quite a big job, so here goes:

Begin by mapping the Mullard valve (tube) tester

First: It is important to have a known good reference valve (tube) at the ready. But much of the setting up of the valve tester is actually done without a valve in the valve holder. This is because it is difficult to access valve pins with the valve in circuit.

The idea is to  mimic the valve parameters for: Anode voltage, screen voltage, grid negative supply etc, by using a resistor, potentiometer and a multimeter to set up the tester, before eventually plugging in a good reference test valve (tube) for testing.  

Find technical info on the valve in order to make the test card (say for example an EF80):

EF80 Ratings:

Voltage anode (Va) = 170 volts (pin 7)

Voltage screen (Vg2) = 170 volts (pin 8)

Cathode = (pin 1)

suppressor grid = (pin 9)

Shield =  (pin 6)

Voltage control grid (Vg1) = -2volts (minus) (pin2)

Voltage heater = 6.3 volts   (pins 4 and 5)

Current heater (Ih)= 0.3amp

Current anode (Ia) = 10ma

Internal resistance (ra) =  500k

Anode pin select (Mullard tester off, select multimeter continuity buzzer – NO valve (tube) in circuit):

For the following test card set up, the locking switches and push switches on the Mullard tester must be operated according to user manual instructions.

A1, A2, A3, A4, A5, A6, A7, A8, A9, A10   A=Anode

P2  P3  P6   P7  P8  P1   P4   P5   P9  N/C   P=Pin test valve

EF80 Screen grid pin (grid 2) select:

B1, B2, B3, B4, B5, B6, B7, B8, B9  B=Screen grid

P2  P3   P6   P7  P8  P1   P4   P5  P9  P=Pin test valve

 

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

For valves with separate cathode and suppressor g3 grid:

Reference example: EF80: S (earth shield) and g3 separated from cathode 

Punch D 10, NOT valve pin selector (earth return for cathode select [next]):

D1, D2, D3, D4, D5, D6, D7, D8, D9 (cathode select)

P2  P3   P6   P7   P8   P1   P4   P5   P9 (find cathode pin of test valve) 

Punch D corresponding to cathode pin. Meter cathode point on valve base to chassis of tester = short circuit to chassis.

For valves with separate cathode and suppressor g3 grid continued:

Punch g3 (suppressor grid and S (dotted shield) (ready for voltage application):

E1, E2,  E3, E4, E5, E6, E7, E8, E9

P2  P3   P6  P7  P8  P1   P4  P5  P9 (Select g3 suppressor grid)

E1, E2,  E3, E4, E5, E6, E7, E8, E9

P2  P3   P6   P7  P8  P1  P4  P5  P9 (Select shield).

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

EF80 Grid pin (g1) select:

C1, C2, C3, C4, C5, C6, C7, C8, C9, C10

P2  P3   P6  P7  P8   P1  P4  P5   P9  N/C

Punch C corresponding to grid pin

EF80 Heater pins select:

F6, F7, F8, F9 (F=first) (applies high voltage to heater pin for heater cathode insulation test)

P1   P4  P5   P9 

Punch F corresponding to heater pin

G6, G7, G8, G9 (G8 goes to cathode ray tube indicator position)

P1    P4  P5   P9

Punch G corresponding to heater pin

Guidance: For heaters at pins 4 and 5:

Punch F7, Punch G8.

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

Preparation for heater and filament continuity test (see test below):

Punch F3 and F4 ready for test (indicator series switches) (full description below).

G3, G10 (series switches enabling ht for next adjustment)

Punch G3, G10.

CRT shunt resistors (CRT must be shunted, to enable current to valve under test; and gives spot position later on):

G1, G2, H1, H2, H3, H4, H5, H6, H7, H8, H9 (all parallel scope shunt and spot set up resistors).

Guidance: to get test valve ht up and running, punch G2. H2, H4, H6.

Enabling anode voltage for test valve EF80:

Enable the mullard valve (tube) tester rectifier valve now:

Pair:  M4, M8 (Feed to full wave rectifier anodes)

Punch M4, Punch M8

Mullard tester power up:

Set up anode voltage without a test valve (tube) in circuit

Connect multimeter to valve base anode pin and set up anode voltage according to test valve operating conditions before load resistor applied:

HT Transformer taps leading to rectifier/regulator circuit:

M3, M2, M1, M5, M6, M7

Pairs:  M3, M7 (High)

Pairs:  M2, M6 (Mid)

Pairs:  M1, M5 (Low)

Guidance: Punch at M3 and M7 =170V (higher voltage test valves).

Value of HT to anodes and screens EF80:

without a test valve (tube) in circuit

L1 (resistor), L2 (resistor), L3 (resistor), L4 (resistor), L5 (resistor), L6 (resistor), all parallel resistors

Guidance: Punch L1, L3, L6, L7 for anode voltage =170V (EF80).

without a test valve (tube) in circuit

Screen (g2) voltage:  K10:  Same voltage as anode voltage

K9, Lower screen voltage.

If valve operating conditions require the screen grid to be the same voltage as anode voltage (EF80):

Punch K10.

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

If valve operating conditions require the screen grid to be lower than anode voltage: Punch K9 only (places potential divider resistors in circuit to drop the screen voltage).

Value of control grid bias voltage (resistors in parallel as above) EF80:

without a test valve (tube) in circuit

i1, i2, i3, i4, i5, i6, i7, i8, (i9 for extra negative if required). Adjust for working conditions of test valve.

Guidance: Punch i4, i5, i6 for negative grid bias = -2V.

Heater and filament supplies EF80:

Value of AC heater voltage (secondary TR2): Select only one!

J1 (very low voltage), J2 (tap), J3 (tap), J4 (tap) J5 (tap), J6 (tap), J7 (tap), J8 (tap), J9 (tap max voltage).

Guidance: Punch J5 = 6.3V

K1, K2, K3, K4, K5, K6, K7, K8 (primary TR2)

Guidance: Punch K5 = 6.3V

Place test valve (tube) in circuit, with plasticard punched accordingly and valve (tube) heater should now light up properly.

 

Mimicking anode to cathode

internal resistance (ra) using a resistor:

without a test valve (tube) in circuit

Refer to test valve operating conditions: internal resistance and current of test valve.

Place (500k resistor  to match EF80 internal anode resitance) approximate value resistance between anode and cathode.

Set resistor to give anode current corresponding to operating conditions (10ma) at 170 volts (anode voltage⇑⇑) .

There must be no voltage drop below 170 volts at the anode pin on the valve (tube) base.

Keep resistor in circuit and re adjust G1, G2, and H1 – H9 for spot in upper green position, whilst maintaining exact working current as test valve will require.

Emission and electrode open-circuit test EF80

without a test valve (tube) in circuit

G3, G10 (series switches feeding directly above parallel resistor switches. Punch G3, G10.

For EF80, with working voltage of 170 v, = Punch G2. H2, H4, H6.

High Speed Mullard Valve (Tube) Tester (Analogue Computer) E7600, 1956/57; Amplifier Tubes for Beginners – a quick guide

Heater and filament continuity (deflection of spot to green indicates okay):

without a test valve (tube) in circuit

F3 and F4 (cathode ray tube indicator series switches) are already punched.

F6 to F9 to select high negative voltage to heater (for testing tube) continuity and insulation (Punch F 7 = pin 4 of EF80)

G6 to G9 cathode ray tube spot position indicater (Punch G8 = heater pin 5 of EF80).

Heater-cathode insulation test (spot dips if shunt test valve is leaky):

without a test valve (tube) in circuit

E1, E2, E3, E4, E5, E6, E7, E8, E9 (Cathode already selected) Selector switch on valve tester to position no 3.

F6 to F9 (heater already selected above).

F4 (indicator on switch) already punched, see heater and filament continuity test above). 

L9, L10 (Value of negative voltage to heater pin):

Punch L10 (as in EF80 reference). This is the higher negative heater cathode voltage.

M10: Dot position adjuster. Observe spot for upper green position, ignore M10. If spot is not in upper green, punch M10 to elevate spot to green.

Electrode insulation:

without a test valve (tube) in circuit

Object of test: to remove HT; and to earth the following pins: valve anode, screen, control grid, earthy electrodes (cathode and suppressor). Then using side spring switches, apply negative voltage to each of the above in turn, while all others are still earthed.

Valve tester off:  Turn test knob to position 2 (HT off).

F4 indicator switch, already punched, see above heater and cathode continuity test.

A1, A2, A3, A4, A5, A6, A7, A8, A9, A10 (Anode already selected)

B1, B2, B3, B4, B5, B6, B7, B8, B9. (Screen-grid already selected).

C1, C2, C3, C4, C5, C6, C7, C8, C9, C10. (Grid already selected)(Goes directly to chassis when test switch is in HT off position).

E1, E2, E3, E4, E5, E6, E7, E8, E9: (Cathode already selected)

D1, D2, D3, D4, D5, D6, D7, D8, D9 (already selected).

D10 (already selected).

Electrode insulation (Fig 7) continued:

without a test valve (tube) in circuit

Object of second test: to apply HT to anode; to earth screen, to earth suppressor grid and cathode (earthy electrodes); to apply normal control grid bias.  Then using side spring switches, apply negative voltage again to chosen pins in turn, while all others pins are at the above voltage.

Grid current (gas) test:

C1, C2, C3, C4, C5, C6, C7, C8, C9 Already selected (see electrode insulation test (fig 7) test above).

E1, E2, E3, E4, E5, E6, E7, E8, E9 Already selected (see Heater-cathode insulation test above).

i1, i2, i3, i4, i5, i6, i7, i8 already selected (see HT and grid-bias supplies above).

END OF ANALOGUE PROGRAMMING.

The Above information was passed to Bernard (GURU) Garland, who set about to design a rectangular steel sheet, which precisely matched the dimensions of a data card template.

Holes were then drilled in the steel sheet which coincided exactly with the position of the holes in several template cards; and which lined up perfectly with the matrix switches in the tube tester.

Next, Bernard created a jig, which held the steel template in the correct longitudinal and latitudinal positions – ready for a blank plastic card to be placed beneath it. 

GURU Garland card making jig for high speed Mullard valve (tube) tester (Analogue Computer) E7600, 1956/57

1: Ensure a flat ripple free surface. 

2: Place metal template on the plasticard.

3: Mark and cut along the edges to reproduce a blank punch card.

4: Place blank card on card maker ⇓⇓and cover with metal template⇑⇑

5: Drill small holes first according to type of valve (tube) characteristics.

6: If no punch available, use router to enlarge the holes.

Making sure everything is lined up

Job done!

This time 2 punch cards for an EL84 Audio output valve

And finally: shot taken in very low light of a known GOOD reference valve running on a plasticard homemade data card

I hope you have enjoyed this extensive article on the fantastic Mullard valve tester.

For Amplifier Tubes for Beginners – a quick guide, please click this link: 

https://electrosparkles.com/amplifier-tubes-for-beginners-a-quick-guide

 

Also, here is another website for you to explore the Mullard valve (tube) tester:

https://mullard.org/blogs/news/bb

 

I should be very grateful to all visitors if you would please do me a great favour by copying and pasting https://electrosparkles.com/ on your social media accounts, in order to bring together like-minded people, who might wish to pool their technical knowledge.

I thank you

Dorian

 

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