Hickok 752 tube tester quit reading mutual conductance

rufleruf

Poor Impulse Control
I don't see a test equipment forum so I thought I'd post here.

After a couple years of reliable service my 752 is suddenly not reading mutual conductance. All other tests seem to work, and the fuses are okay.

Any ideas?
 
Yep - continuity through it - learned about that recently with a mislabelled 12AX7.

After I posted I went and did the "Tone Lizard" tube tester basic fault tests. You set it up to test a 6L6 and test the voltages across some pins of the octal socket. The voltages were pretty low compared to spec for a 6L6. I opened it up and the 83 tube looks rough - no getter flash left and loose in the base, so I ordered a SS replacement yesterday. I am hoping this is all.

Last tube I tried to test was a little 0A2 and it gave me heck, so I think I 'did in' the already weak tube.
 
Any caps in your tester? Usually there are one or two. Have they been replaced?

Funny I was just looking at a 752 the other night that I acquired awhile back and is parked in the 'repair and restoration' pile.
 
Matt; There is no getter in a Mercury vapor tube. The loose beads etc in the bottom of the tube is mercury. Turn on the unit with the tube vertical and let it cook for about 30 minutes or so. The mercury beads will heat up and vaporize into the vacuum. If there is a 6H6 tube in it and you have another swap and test the old one. Same with the 83.

With the SS replacement watch the voltages. It's similar to putting a SS Bridge in a 400 without a dropping resistor. Check your voltages against the schematic 1st before putting in the SS Repl.

Larry
 
Also you can glue the loose base back. I can't remember whether people like Superglue, clear silicone or what.

I thought those 83 tubes didn't work that hard in the Hickok and should last a loooong time.
 
Dropped in the SS replacement (before I read your comment Larry) and it now works. Retested a few EL34's I did right before it stopped and they all test as they did before it stopped.

I didn't see any caps, but then I didn't really look. Some oxidation on the various pots - maybe time for a deoxit tune up.
 
NO DEOXIT on Tube tester pots! NADA, NONE, ZILCH, ZIP!! Just work the living hell out of them. (you've probably done it before I posted......IF SO go down to Home Depot and get some CRC QD ELECTRONICS CLEANER! FLUSH EVERYTHING YOU PUT DE-OXIT ON AND EXERCISE THEM EXTENSIVELY!).
 
I'm still out of deoxit - and have a pile of fishers with unhappy pots to work on.

Maybe it's time to buy that Amplitrex or RoeTest tester and pass the Hickok on.
 
I take it the no Deoxit has to do with getting the oily stuff soaked into the phenolic wafer switches?

I read somewhere you can take a strip of stiff paper or cardstock, wet it with solvent and slide it between the contacts on wafer switches. Cleans only the contacts, no mess on the wafers.
 
I've been over to antiqueradios a few times, but am reluctant to get active in yet another forum. Too bad AK doesn't have a test equipment / tools discussion area.
 
I have a 600A which I went thru, I changed most all the resistor's (even the hidden 47ohm) within
the controls, and the one cap by the short switch. So far it's working good I'm getting good reading's
on all my tubes, some I thought were good weren't and that's the goal. I think if you could get the manual
and schematic it's a great help getting these guy's working right.
 
NO DEOXIT on Tube tester pots! NADA, NONE, ZILCH, ZIP!! Just work the living hell out of them. (you've probably done it before I posted......IF SO go down to Home Depot and get some CRC QD ELECTRONICS CLEANER! FLUSH EVERYTHING YOU PUT DE-OXIT ON AND EXERCISE THEM EXTENSIVELY!).
 
Thanks Larry,
So I got a Precision Apparatus 920 that looks really clean, all the papers, supplements books and tube adapters.
I popped the cover off and looked under neath before firing it uo and there are 2 wires off. Looks like one goes to the main tube and the other appears to go to the F position adjustment I can't figure it out from the basic schematic I found. ( But thinking I was doing the right thing, I did the DeOxit on everything, so off to Home depot for the CRC Electronics cleaner. Would anyone on this sight be able to ID where the disconnected wires go on this Tube tester? I have pictures and I think the schematic for it?
Thanks again for clearing up the DeOxit use, just happened on this.
What about on the sockets? Clean them also?
Ken
 
Tube sockets should be cleaned with contact cleaner only, and switches lightly clean with it as well. I read
on line the Deoxit leaves a film on the switches that might effect the readings of the tube tester.
 
The 'film' is what prevents the surface from corroding in the future. I have not heard of it affecting circuitry. Not that I know everything, it's just a new one on me.

I use DeOxit (on a piece of cardstock as described above) and follow with DeOxit Gold which is designed to protect contact surfaces from corrosion.
 
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