[TV MAN]

Hi all! I am getting ready to set up shop again for the winter and tackle some projects. I decided it was time to upgrade to a better tube tester. "Want" or "need", I am not sure of - yet, but this is an instrument I will be using frequently over the years, so I settled in for a Hickok 600A from Ebay. Didnt get a super deal, but nowhere near what I have seen them sell for either. It wasnt in the budget to get a calibrated, ready to go unit, so in typical "me" fashion, I found something that appeared decent and was described as "working but needs calibration". Well, as usual, NOTHING I get from Ebay actually works properly without some TLC, and this tester is no exception. So, in saving the extra $300+++ I could have paid for a properly working unit (which may ALSO need overhauled), I am ready to get out the tools and get this working right!

   

This is a nice, clean "estate" find (per the description). It does power up and test tubes. Overall, it does appear to be a nice tester. I chose a model 600A because is seems to be the "Chevy" of the tube testers, and seems to be support and parts out there.
 I downloaded a manual from BAMA, and found calibration instructions from Danial Schoo (from 9-2006) and a few bits and pieces here and there. This will surely be a familure sight to many.

This is a completely different instrument than my Eico 625, and the manual I downloaded seems a little vague in details, in which I am sure many here will be familure with. So, I will have some basic questions. I welcome any tips, how-to's and comments as I attempt a restoration. In not seeing any other (recent) threads on restoration of a 600A, I thought it might be interesting to get one going.

[morzh]

One thing that doc mentions as I remember it is a Voltmeter with 1Kohm/V resistance. This was the reason I bought one.

[tab10672]

You do know about the red dots on the English dial? The chart English numbers were a little confusing when I first got mine until I figured out why the dots were there.

[morzh]

Yep, I also had to inqure.....even with manual I needed someone to explain things.
Also English itself, being the alternative way and shown in tubes' chart might be confusing.
And sometimes, like for diodes, English is the only way shown.

[John R]

Tim,
If you need here is a comprehensive tube setup list.
http://www.saegerradio.com/downloads/Con...20V2.5.pdf
John

[thirtiesradio]

I have one that I have calibrated over the years several times. Not too difficult to do but I had to use a VTVM for some of the voltage readings.

[Alan Douglas]

Does it need "calibration"? Versus needing its switches exercised to clean off a few decades of tarnish? That's the usual problem.

[TV MAN]

I was a little confused about the English dial myself, but do know about the red dots. I am guessing that if I want to read the meter in mutual conductance, I set it to one of the dots within the range of what the chart calls for? And, that I use the "replace-?-good" reading I set to the number listed? Another question I had is about the Gm number; is this the minimum value for pass-fail?

I assume this tester has been idle for years, maybe decades. I havent really decided if any of the controls are dirty or if it is the way it operates. I made a few quick checks, but dont have the 1k per volt meter handy, so I used my Fluke 77. Plate B+ is really high, just under 200v, screen voltage is right on at about 131v. Reduced screen also on target at about 57v. Bias was a little off at -41v. Grid signal also right on at 2.5v ac. I know this may be off some due to not using the proper meter for some of the tests, but gives me an idea of whats there. Line control did seem a little flaky - seems to run high, but it will adjust with a tube in a socket for testing (6V6GT).

I pulled the cabinet to visually check over, and found the 83 tube replaced with silicon diodes (they did use a tube base), 5Y3 was in place. This could explain the abnormally high plate voltage and the flaky line adjustment. Still has an old E-cap across the meter. I saw where the english control had "been into", but it does seem to work fairly decent. This is as far as I have gotten. I also appreciate the link to get an updated tube chart. I noticed the lack of some newer tubes such as 6BQ5, 7591A.

Thanks for the replies so far.

[tab10672]

You set the red dot to the scale of the "mutual conductance" rating for the tube being tested not the range of the English number listed in the chart. You use English only to test emissions (good/replace scale)

Yes the gm number listed is the minimum acceptable reading but it can test well above that if the tube is new. And just because it tests under doesn't mean the tube is bad, just weak or worn but still may be usable depending on its application.

[thirtiesradio]

I remember the first time, about 15 years ago, that I calibrated my 600A.  Some voltage readings were close and others were way off. It was very confusing at the time as I found the tester was reading correctly when I tested the same tubes on a friends 600A. I called the person across country who had calibrated, and sold my friend his tester. He told me to use the correct meter and with it I found all readings were correct.

[Phlogiston]

Probably the most important thing is to make sure that the filament voltages track with the scale (on the control) and with the line voltage (centered on the meter).

I really like mine, but the BK 707 is a lot easier to use.

[Alan Douglas]

Plate voltage will read high unless you use a meter that loads it down (1k ohms per volt was recommended, or a 250k shunt resistor). The reason is the small mica capacitor, which acts as a filter capacitor and charges up to the peak at light loads.

I think your tester is working normally.

[TV MAN]

I made a few more checks and found with the 250k shunt resistor that voltages checked out more closely. I tried some testing and things seemed to work decent except for a sticking meter when I use it on its back (sockets up). Sticks right at the "G" on "good". When I operate it with the sockets facing me as I had been to see the roll chart while sitting, it works ok. Dollar signs all over that one. Any advice on this? I dont know if taking things apart and blowing gently with low pressure air may help or some instrument oil may fix?

[Mondial]

If you are careful, you can disassemble the meter and clean between the magnet pole pieces and the movement coil. Typically there will be a particle in this area which causes the coil to rub at a certain point of deflection. Shine a strong light from the back of the movement and look between the poles for any foreign particles.

Another possible problem may be metal whiskers which will grow over time from the plating on the pole pieces. I have repaired this condition by carefully scraping the inside surface with a thin toothpick.

Would not recommend using any oil or lubricant as it would not help the condition you are describing. Check to see that there is not too much axial play in the movement pivot bearings, which would cause the coil to drag against the poles when the meter is horizontal.

[Alan Douglas]

Unless you have good close eyesight (or a binocular microscope), and steady hands, you're better off just living with it. If you do try, find a clean area (meter magnets can attract particles from interstellar distances) and use slivers of masking tape on toothpicks in the gap to remove the bits of corrosion. Absolutely no compressed air, no magnetic tools, and don't touch the hairsprings.