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Any difference between old and new 7868's (Tube Tester related)

captouch

captouch

Addicted Member
I'm at a loss.

I have a Hickok 536, which doesn't have a noval socket. It does test 7591's on the octal socket though.

So I built an adaptor to enable a 7868 to get tested on 7591 settings. Basically a noval socket, wire routing to an octal base.

It works fine with my EH 7868 tubes, no problem.

However, when I try to test another AK'er's old (GE) 7868's, I get nothing. The tube warms up, but no Gm reading at all.

At first, I thought maybe I stretched the socket with my new EH, so I built another one with a fresh socket. Nothing.

Then I thought even the new socket might not be tight enough, so I re-tensioned all the socket holes and tested for continuity with a DMM. Continuity was there.

Yet this old tube still doesn't want to show any Gm at all.

Took the same old tube to another emissions tester I have, and it tested fine.

Just trying to figure out what the issue might be. It seems doubtful that they'd change something fundamental that would result in a new issue tube testing as expected and an old tube not giving any reading. . .but I'm at a loss, so thought I'd put it out there.

Ideas?
 
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Well i heard the tube pin size is larger on the new tubes and may open the tube socket female contacts too wide to test the original ones :tears:
 
as far as I'm aware, the pinout on the old and new are identical. Did you tie pin 2 and 6 together on the Novar socket ? 1 and 7 I think also go together. 2 and 6 are grid 1, 1 and 7 are the screen. Maybe the old tube doesn't have the internal connection between those pins, so you have what amounts to an open terminal when plugged into the adapter?

If its not that, I got nothing.
 
Well, here's the wiring I used:

White Noval Socket > Black Octal Base

1 > 4
2 > no connect
3 > 5
4 > 2
5 > 7
6 > 6
7 > 8
8 > no connect
9 > 3

I didn't tie 2 & 6 together as I thought the tube would take care of that. I just measured 2 & 6 with a DMM and it's shorted in the tube.

Weird thing is that this adapter works on a new EH tube but not the old GE.

I built the second adapter today (identical to the first I built awhile ago), just for the reason that I was wondering whether my new EH opened up the female contacts too much. When the new adapter didn't work, I made the female contacts even tighter - so don't *think* it's a contact issue, but you never know I guess.
 
If it were mine, I would make the wire connections even though they "should" be connected inside the tube just to see if it did make a difference. And also check those GE tubes after testing- those you already tested because I have burned out internal connections on other tubes, and they did not always arc visibly when they did burn through.
 
does anyone have the wireing for a Hickok 1050-144 adapter?
Needed to test 7868 on 533 tester. Not to convert from or to a 7591 either.
I have tried all the other iterations of wireing scheems and none of them work.
I even did a straight 9pin to 8pin leaving the NC pins NC. didnt work.
Only the 1050-144 adapter will work.
 
Huh. An octal-to-novar, 7591-to-7868 worked great on my TV7 (using the 7591 settings). Wonder what the significant difference would be with another Hickok tester, in terms of needing a specific pin-out?
 
Trio said:
If it were mine, I would make the wire connections even though they "should" be connected inside the tube just to see if it did make a difference. And also check those GE tubes after testing- those you already tested because I have burned out internal connections on other tubes, and they did not always arc visibly when they did burn through.
Click to expand...

Shorted 2 & 6 on the adapter, but still didn't work. Still a mystery, unless this particular tube is batty.
 
GordonW said:
Huh. An octal-to-novar, 7591-to-7868 worked great on my TV7 (using the 7591 settings). Wonder what the significant difference would be with another Hickok tester, in terms of needing a specific pin-out?
Click to expand...

Yes, the adapter works for my new EH 7868's too. If I can get my hands on another old 7868, I'll try it and see how it does. Could be this particular tube although it tested fine on another emissions tester and was working OK in the amp it came from.
 
Just to tie up loose ends on this, looks like it was the particular tube. We tried another vintage tube and were able to get a Gm reading.

So the adapter seems to work after all.
 
corrext me if I am wrong captouch, but didnt we determine that it works only on your Hickok but not on mine, 533? At least I thought we did.
 
Well, the Bogens tube have us a Gm reading on your 533 using 7591 settings, whereas the GE did not - I believe the GE is bad on some level. I'm sure the Bogens tube would work on mine as well. The question is whether the Bogens would read the same Gm on mine and yours - we could test that next time. But different Hickok models can also give different readings.

I believe your Gm reference value for the 7591 (8000 if I remember correctly) was an average new value. So 60-65% of that (4800-5200) should be min good. My reference values are min good and 5000 if I remember correctly. So I guess they should read similarly on both our testers. We could try multiple of your tubes next time to see how closely they really match. Can't use my new issue tubes or they'll stretch out the socket pins.
 
U R rite. we did get a mediocur reading on 1 tube. but nothing conclusive. I would just like if someone would give the correct wireing for the hickok adapter 1050-144.
 
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