View Single Post
Old 6th May 2014, 4:41 pm   #93
ukcol
Rest in Peace
 
ukcol's Avatar
 
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
Default 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.
Attached Thumbnails
Click image for larger version

Name:	Pins 7 & 8.JPG
Views:	317
Size:	5.7 KB
ID:	92540   Click image for larger version

Name:	Bush TV83.JPG
Views:	311
Size:	10.1 KB
ID:	92541   Click image for larger version

Name:	Philips 1792U.JPG
Views:	311
Size:	9.3 KB
ID:	92542  

Last edited by ukcol; 6th May 2014 at 4:54 pm.
ukcol is offline   Reply With Quote