Mullard Valve Tester Card Project

[theredhouseinn]

Hi Stan
My missing card numbers.
18,24,28,29,40,70,71,73,76,84,87,232,240,250,252,3 42,3511,375,410,428,430,459,481,482,483,503,557,58 8,602-609,644,647,648,651,652,662,664-668,673-705,715,716,718,721-753,761-786,797-928,948,952-956,9611,962,964,968-975,979,980,981,983-995,1003-1017,1020,1021,1023,1027-1054,1056,1062-1103,11106,1107,1117,4420,1122,1123,1124,1126,1129 ,1133,1137,1138,1142,1145,1147,1150,1151,1152,1154 ,1155,1160,1160,1165,1173,1174,1182,1197.
that's the lot Stan. I used the Mullard numerical list to check my cards. Where I have grouped numbers I have probably included non-issue card numbers. Appologies for this.
My email address is - [REMOVED BY MODERATOR,SHARE BY PM] - I didn't realise that I had so many cards missing, if it is easier for you to email me the file, please do so.
Incidentally, since my complete refurbishment of my tester, it appears to be working perfectly on the valves tested so far.
John.

[Electrical]

Hello John
I have just finished rescanning the images you sent and I have converted them to pdf files, please see attachment.
I will check and see if I have all the cards you have requested and I will ask one of the moderators if I can post the files on the forum or if they would prefer I sent them by email. I will send you a Private Message (PM) when I have collected all the data and let you know the best way to send it.
Regards Stan.

[Chris55000]

Hi!

Has anyone been able to compile a definitive table of the gate switch functions yet?

I've tried doing it from the Mullard Service Manuals for the E7600/3 and E7600/4 but don't seem to have much luck!

Obviously the first few rows that connect the valveholder tags to the circuit are fairly obvious, it's the ones that select the H.T. and G.B. voltages from the voltage stabiliser circuits by changing over resistors (or combinations of resistors) that seem to be a stumbling block, since there are (theoretically!) up to 255 different function combinations!

The contacts towards the bottom that select heater voltage from the heater voltage transformer are, of course only operated in such a way to connect two distinct taps to the valve–holder supply points at any one time, so a table for the transformer tap gate switch configuration can be drawn up from knowing what the heater supplies from the transformer are, and this data isn't in the manuals! (Or have I missed noticing it somewhere?!)

Incidentally, did Mullard provide selectable anode resistors for Magic–Eye Valves, or was the Magic Eye Triode Anode voltage selected by the normal method for any valve, by selecting the appropriate resistors in the H.T. stabiliser?

(I haven't yet had a chance to study the circuit diagrams in great detail, but me thinks if there are four contacts spare, then these could be used for m.e. triode anode resistors, e.g., 100k (EM87), 470k (EM80/EM81/EM84/EM85), 1M (end viewed, single shadow octals) and 2 × 1M for the EM34.)

Chris Williams

[Electronpusher0]

I have posted the attached table on another thread, it is (still) a work in progress but like you I have traced the switch functions from the schematic.

Peter

[GMB]

There are interactions between the features so it isn't trivially simple.

By way of example, you might have expected various holes to select the heater voltage, but actually you find cards with different hole combinations in the heater area for valves with the same heater voltage rating. The reason is that they actually allow for the effect of the current drawn loading the transformer.

[PJL]

I posted an emulator that runs on Microsoft IE here. https://www.vintage-radio.net/forum/...d.php?t=155140

The emulator displays the test conditions for a card for all operating modes and I went as far as emulating the testers valve characteristics. It includes the hole layouts for some cards but these should not be relied on and you should check the hole settings match those on your card before making any assumptions.

The javascript program is included so you can see how it's all done.

[Chris55000]

Hi!

Originally Posted by GMB

There are interactions between the features so it isn't trivially simple.

By way of example, you might have expected various holes to select the heater voltage, but actually you find cards with different hole combinations in the heater area for valves with the same heater voltage rating. The reason is that they actually allow for the effect of the current drawn loading the transformer.

This is something else that my study of the manuals didn't pick up and I'm not sure the military version CT80 manual makes it clear either!

To take 6.3V valves as the most common example, you've got currents ranging from 90mA for the EY51 e.h.t. rectifier to over 2 or 3A for many of the smaller glass–base transmitting tetrodes, etc. – the only way to determine the characteristics of the heater transformer for certain is to connect a controllable variable a.c. load with a reliable current–monitor to it – I think I've seen a project for a continuously controllable one somewhere, but it's not a trivial design by any means!

No doubt Mullard's design engineers were provided with loading graphs for the heater–voltage transformer, but it's certainly info I don't recall ever bsing documented anywhere!

Chris Williams

[PJL]

There are multiple taps for some standard voltages. I am not sure if this is related to the valve manufacturers specification or the loading on the LT transformer although I expect the latter. I have also not checked to see if the tester intentionally runs with a low LT (-5%).