Re: Mullard Valve Tester Card Project
(See post 89 to 92 above).
I believe I have solved the "problem" of cards 713ABC.
As mentioned cards 713B and 713C are almost identical except for 2 contacts. On card B the tester connects to the lower triode of the ECC84 via contact D4 of the gate switch to pin 7 of the valve. Card C uses contact D5 of the gate switch to connect to pin 8 of the valve.
The valve has pins 7 & 8 connected together internally (see picture) and are for the cathode of the lower triode. This valve is designed to be used as a cascode VHF amplifier in TV tuners, hence the term "lower".
So it follows that card B tests the lower triode using the pin 7 cathode connection and card C tests the same triode using the pin 8 cathode connection.
In my picture of the ECC84 the cathode connection comes out at pin 7 and the added link goes to pin 8. I have concluded, therefore, that this is not a mistake by Mullard and that the third card is to test the integrity of the pin 7 to pin 8 link.
A similar argument can be made for cards 655ABC (for the PCC84) and cards 911ABC (for the UCC84).
I have also included pictures of 2 circuits using a PCC84; In the Bush one pins 7 and 8 are not joined externally to the valve, in the Philips circuit they are. If the weld failed on the link inside the valve the Bush may display a fault symptom whereas the Philips may not.
Edit. I mentioned in an earlier post that the tester displayed a slightly higher emission an card C than on card D; whether or not this observation was real or imagined, it was nothing to do with the change of cards.
Last edited by ukcol; 6th May 2014 at 4:54 pm.
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