Hickok 752A calibration?

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mksj100

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Joined 2007
Pretty stiff on the transformer rewind, but then it is a lot of work and time. Another option might be to use/fit a toroidal transformer that has dual independent secondaries. You would need to account for the primary side voltage which I assume it is 100V on this model. AnTek has a number of inexpensive dual voltage dual isolated secondary windings toroid transformers. Something like the AN1T200 ($29.00), would give ~203V unloaded at 120V, so ~170V at 100V input (both secondaries would be used independently as opposed to parallel) Antek - AN-1T200 . Toroid transformers would be a bit stiffer, so may not see as much sag under load, but you could always pad it on the primary side. Not sure how it would operate in the tube tester circuit, but I have done something similar on the filament transformer to allow testing of some high current tubes. It's been an informative discussion, will bow out at this point.
 
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dgta

Member
Joined 2011
Guys, looks like I can get an Antek transformer with TWO 170V secondaries pretty cheaply but need to be careful specifying it.

Can anyone tell me how much the plate voltage (150VDC) droops with an actual tube under test drawing current? For example, a 6L6 at whatever the test current is (20-30 mA?)

Edit: wow, I was just researching Antek while you were posting, how coincidental can we get? :)
 
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jimmy74

Member
Joined 2009
I've just received my hickok 752A tester, but the meter doesn't work, I turned it on and it turns on ok, but when adjusting the line adjust, the meter is just still though I can hear the hum increase as I trun the line adjust knob, so I don't think it's a tester problem, just the meter stuck? any ideas as to how to fix this?

thanks
 
G

glassandlight

Member
Joined 2007
jimmy74 said:
I've just received my hickok 752A tester, but the meter doesn't work, I turned it on and it turns on ok, but when adjusting the line adjust, the meter is just still though I can hear the hum increase as I trun the line adjust knob, so I don't think it's a tester problem, just the meter stuck? any ideas as to how to fix this?

thanks
Click to expand...

If you bought this on ebat, and the description did not state this issue...SEND IT BACK, and file >>>>>>>not as described! Don't open it up or fool with it.

There are many reasons why the meter is not responding (your description needs revision it is not very clearly written).

Here are possible reasons why it 'doesn't work':
1 coil is fried
2 debris on the meter magnet core holding the needle in place
3 bad 83
4 broken wire
5 shorted smoothing cap.
6 open dropping resistor

if it is 1 or 2 to have a real problem, a $175 problem to have the meter rebuilt. #2 can be fixed but you better have done brain surgery because it is that delicate.

The hum is overload on the transformer because you are well beyond the line adjust point.

Become an educated consumer, ebat is full of idiots who do not have a clue what they are doing or what they claim. By the way, for anyone who reads this, gm DOES NOT match tubes only plate current matches tubes. gm is the A.C. component, current is the D.C. component of the tube
 
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jimmy74

Member
Joined 2009
no it wasn't an ebat tester, local seller who sent me a 10 minute video of himself testing different tubes and showing everything in perfect working condition, I think the octal socket saver (which was not plugged in) went bumping around during shipping and may have knocked on the meter itself.
 
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jimmy74

Member
Joined 2009
Ok I've just removed the meter and it basically fell apart showing the insides, it is broken... hard to describe but there are 2 copper plates screwed to 2 pieces of plastic which were obviously part of the meters back cover. Any good service technicians in Europe? I'd probably be needing a new meter though! It doesn't look like an easy fix.

thanks
 
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mksj100

Member
Joined 2007
Are you pressing the line adjust button when adjusting the rheostat and checking the meter? See if there is any meter movement with the bias adjust. You could put a milivolt meter across the meter terminals to see if there is voltage to the meter. If you check it the meter has an open coil with an DMM ohmeter, you will quickly fry the coil if not done correctly. You need to put the DMM meter in the manual range (NOT AUTO) and set it at something like 1 megaohm range, and measure the DMM microamps with another DMM or check the factory specs, you want something like 10uA. There are other ways to check the tube tester meter with a small battery and resistor networks.

Check if the meter moves when the tester is turned back and forth ~90 degrees on a flat surface. If the needle does not move, it may have jumped the movement, if it swings wildly (not dampened), you probably have an open coil.
 
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jimmy74

Member
Joined 2009
I think it is pretty much broken, here are some photos:

https://www.flickr.com/photos/73835524@N00/sets/72157650604100900/

Useless trying to glue back the plastic parts because the copper plates that a screwed to them would snuggly fit between the meter mechanism and the meters indication panel (this makes me wonder how on earth they put it together in the first place). The other thing I noticed that would make me opt more for a replacement than trying to repair this one, is that the small calibration screw on the front of the meter, used to place the needle to absolute zero, doesn't move the needle at all.
I had already contacted All tube testers before so I will now contact the other 2 companies you linked.

thanks
 
T

tonekwest

Member
Joined 2011
I have repaired meters that were broken as yours is. If the delicate needle/clockspring mechanism isn't damaged and all of the wiring is still intact, there is still a chance. You stated the needle zero screw has no response after attempting repair. The yoke, forked part of the actual movement, needs to be in the position where the adjustment screw is in the center. The screw is actually a type of eccentric and moves the yoke left or right a small amount. "very hard to explain" but I hope this helps.
You have nothing to lose since it's already broken :D
 
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