807 Testing.

[Diabolical Artificer]

Been testing some 807's today to try and get a matched quad. Out of around 25 807's I found three faulty ones.

The first iffy one was a JAN - USA made 807 with an OC heater, it was NOS, still in the box. Tried resoldering the pins, then when that didn't work I took the base off. There was still no continuity between the htr wires. On closer inspection through a magnifying glass, I saw that one side of the htr wasn't even connected to the bonding wire, in fact the bonding wire was over to one side, not even close the htr. See pic - NC htr RHS with bonding wire about 1/4" further to the right almost touching G1 bonding wire.

The next two behaved oddly, showing way over the top Ia, 140mA + , when they should have been around 30mA. Control grid not connected maybe, no, that was ok on both. After more fiddling about and controlling Ia by reducing G2 voltage I noticed the G1 bias voltage drop to 0v if I turned up G2 voltage, so a short between G1 and G2.

However the other is a mystery, no shorts detected but the valve just runs away till the anode glowed red. Again the control grid worked ok, so maybe a G1 cathode short?

Andy.

[BusyBee]

From the photo it looks like that had never worked Andy. I would have presumed that all valves were powered up on a testjig before boxing, but maybe not? I have tested all the (western) valves I buy as soon as I receive them, and luckily found no issues, so that sounds a very poor batch. Maybe the box has been dropped at some time in the past?

Tracy

[Diabolical Artificer]

Yes Tracey, you would have thought so. My friend who sent it me from the USA was of the opinion that the postal service was to blame, but the valve has little mass as does the htr bonding wire, which would have been contact welded to the htr itself, it would take a prodigous knock to dislodge it.

Going to put the crazy 807 in an amp, to try and see if oscillation is occuring.

Andy.

[radioman]

I've got a couple of 807's - one tests perfectly but the other one appears to oscillate on my AVO valve tester and only stops if I lower the screen-grid voltage.
There is some interesting background information about 807's that ended up on the surplus market here :-http://www.r-type.org/addtext/add029.htm

Andy

[Diabolical Artificer]

Thanks for that link Andy. The 807 with an OC heater was of inferior construction in comparison to others I have. The mica spacers were thinner, there were no ceramic spacers for the anode , the anode was made of thinner steel, there was no ribbed "clamp" under the anode and lastly the getters were simple bars of some dark metal, not the usual dish. It was a JAN valve which I think stands for Joint Army Navy, so intended for military use; you would of thought the standard to be higher.

I'll chuck the runaway 807 in an amplifier and check for oscillation, however my homebrew tester does have ferrites on all valve base pins, one ferrite in the anode cap and other anti oscillation measures.

Andy.