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Eico 625 Tube Tester Query

5

54321James

New Member
I am a true novice tube tester. I just purchased an Eico 625 tester. The manual says "Adjust LINE ADJUST potentiometer until meter reads within a division of "Line." This is a little vague to me. The meter shows a red area (labeled REPLACE), a yellow area (labeled WEAK with "Line" above it), and a green area (labeled GOOD). Do I adjust the LINE ADJUST pot so that the dial touches the dark line between 400 and 600 under the LINE in the center of the WEAK yellow area? Do I return the line adjust pot to the suggested selector setting BEFORE pushing the merit button, or do I leave it in the line adjust position and then press it? I am very confused...
 
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I'm not familiar with the Eico 625, so others more knowledgeable will jump in, but if I'm understanding you correctly then yes, move the selector knob to the proper selection *after* using the line adjust knob to center the meter needle on the "line" marking.

The "Replace", "Weak", and "Good" designations (and the numbers) on the meter are meant to be referenced after the switches and selectors are in place for a specific tube.

My understanding is that because of fluctuations in mains voltage (the voltage coming out of your wall socket), it's best to do the line adjust process before checking every tube in order to ensure that you are getting correct readings...
 
54321James.

I've had a 625 for over 10 years and it does yeoman duty testing for Go-NOGO conditions. And that's all it'll really do.

Turn on the Unit. DO NOT insert a tube, YET! Set the Selector switch on the right side (1-2-3-4-LINE) to LINE. It should come up to close to the line in the CENTER OF THE METER marked "LINE". If it's Over or Under, rotate the Line Adjust POT on the LEFT SIDE of the unit below the Heater voltage switch. Once centered leave for the session. Do this 1st EVERY TIME you turn it on.

Turn the BIAS andENGLISH pots to the setting for a tube (use the latest roll chart on the Boat Anchor Archives site..the chart usually in them is in accurate.) Set the Selector (1-2-3-4-Line) switch per the manual for the tube. Set the heater voltage, and with ALL of the switches 1 thru 9 in the middle, insert a tube. Then set the 1 thru 9 switches Up or Down as required for the tube. Numbers in Parentheses get thrown to center or opposite pole together during testing). Wait a minute for the tube to warm up. Press the Button on the lower right hand corner and the needle should give you a reading. Note that EVERY 12ax7, 12AT7 and 12AU7 I test with setting to each specific tube will give about 58 to 62. Dont dwell too much on the number. The 625 is a rather basic Emisions tester and it's more of a culling machine in that you can do a GO- NOGO test only. That's really enough for 90% of the stuff starting out.
 
The proper thing to do, is adjust the line control after the tube is setup in the chart, and inserted, because a tube that draws more filament current will draw down the voltages in the tester, more than tubes that draw less current
 
Thanks so much for your input on this question. I have 100's of tubes that test in the WEAK area on this 625. Is that normal? I mean, even NOS tubes in original boxes and clearly never used test as weak..?
 
@larryderouin will be able to answer your question specific to the 625, but with my Hickok 752 the dual triode tubes (especially the 12AX7) tend to test lower than they actually are. I don't know why, but from what I understand this is a known issue with some testers and just needs to be factored in.
 
Set your Line Voltage 1st. After setting up the tester with the tube, and letting it warm up, recheck the Line voltage (thanks Scott, I forgot that part) then test. IIRC there are only a couple of caps and resistors inside the 625. You might recap using 10% variant caps (if possible otherwise 20% is fine)and replace the existing resistors with 1% variants. It's been about 10 years since I opened mine last. DO NOT under any circumstances, use DEOXIT of ANY TYPE on the 625. IT WILL SKEW READINGS LIKE CRAZY. I tend to use the 625 for a GO-NO GO reading, then use my 533A (Philco 9100 variant) as a final test. I've gotten so I can determine on the 625 what norms are for most of my tube types, but use the 9100 for gm and balance measurements between sections.

HICKOK's tend to give a low gm reading on most all dual triodes. This is a known issue with them. As long as they show gm above the roll chart figure, I call them good for my use.
 
Looks like it uses a 6H6 twin diode tube for the meter. if that is weak, the meter won't read properly. Otherwise quite likely dirty connectitons and/or off value resistors. There isn't a whole lot in there.

+1 the DeOxit, but the CRC QD cleaner does work fine. Basically anything that does not leave a residue will get the job done.
 
Gadget. You think putting in something like paralleled 1n4004 might work in lieu of a 6H6. All it's doing is rectifying to the meter @ 30V input.
 
yeah, voltage drop might be the issue. Honestly I'd stuff another 6H6 in there for a couple bucks and expect it to last the remainder of eternity. Or since I've got junk laying around, maybe fabricobble an adapter to a 6AL5 since I have those.

Its really not a tube that should go bad or wear out doing what it does, but if someone left this powered on for a couple of years for whatever reason it might be weak.
 
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