Help with Eico 950B knob and pointer - Printable Version
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+--- Thread: Help with Eico 950B knob and pointer (/showthread.php?tid=19931)
Help with Eico 950B knob and pointer - redcsctrike - 05-02-2019
I sure hope I am posting this in the correct Phorum. A couple of years ago I purchased a "working" Eico 950. It has a silver face and 950 on the face. However when I compared it to the various schematics, it has the components and values of the Eico 950B.
When I received it, the middle knob was cracked and the pointer for indicating values was missing. I am hoping to make a replacement pointer from plexiglass. I also need to see a view of the knob. Would anyone be willing to make a trace on paper of the pointer? I also need to know how the pointer connects to the middle knob.
When I received the Eico, the middle knob was slightly bent toward the bottom of the tester and I believe it must have been dropped at some point. I have straightened the front piece and the potentiometer with the knob is now straight. I have tested it and the HV reaches 490 or so volts. The eye tube works well and when checking a capacitor I can turn the middle knob and I get the correct response shown on the eye tube. Without the indicator I have no way of telling the reading when I get the widest opening of the eye tube.
I would appreciate anyone's response. I would like to get this operating properly to be able to see values as well as to check for leakage.
Thank you for taking time to read this post and I apologize if I should have posted this in the want ads.
Roger
RE: Help with Eico 950B knob and pointer - Chas - 05-03-2019
FWIR the knob is Dakaware brand. It is a solid Bakelite knob with three threaded holes to mount the cursor. There are plenty of images of this bridge that can be found with a Google search. Simply estimate the taper and width based on where the edges of the cursor appear in relation to the dial scales. There is a scribe line on both sides of the cursor, because it is transparent the lines help to eliminated parallax error. Thus, the cursor can be as thick as desired, so long as it is scribed & inked on both sides.
GL
Chas
RE: Help with Eico 950B knob and pointer - redcsctrike - 05-03-2019
Thank you Charles! Nice to know the pointer has a scribe line on front and rear to reduce paralax. The knob which is present has a smooth back without any way to hold the plexiglass to it. I'll obtain a replacement knob and make the pointer. Thank you for the information. I thought there might be strict dimensions for the pointer. It will be easy to make now that I know what it is.
Everything works great with the tester. Might need an operator upgrade though...
Thank you again for taking time to respond!
Best,
Roger
RE: Help with Eico 950B knob and pointer - redcsctrike - 05-03-2019
Chas,
My sincere apology for calling you Charles. My keyboard needs a new operator too. Not sure why I responded to "Charles". The knob on the tester at present is a fluted knob about 1 1/4 inch in diameter with a brass insert that may have held the pointer. The insert is not removable though.
Roger
RE: Help with Eico 950B knob and pointer - Chas - 05-03-2019
Roger,
Yes, it is Charles.
I use Chas in many forums, seems it was available...
I have capacitance meters, most are old school bridge type.
You will find that long leads will become part of the measurement. In open space, 8" clips leads will give 10pf, twist the leads together and it will go quite a bit higher. So it is best to measure right at the binding posts.
Caps that are leaking a LOT will have a very broad and slight wink to the eye. The overall quality of the cap is indicated by how sharp/deep the null. Really, should not be used to evaluate quality, just the ball park value and leakage under high voltage.
I keep a couple of 1% cap values as standards on the bench, in event I get a out of whack reading...
I found that as I service, I don't bother with common paper caps, just replace. Others that seem questionable and may be a more modern cap I will measure.
Truth be said I seldom use the bridge. It gets pressed into service when the radio won't align, generally, mica fixed padders are off or coil forms have shrunk. So I have to measure to know how far to pad out a cap to achieve alignment.
Oh, I do not know the full functions of the Eico, but if places over 600 volts on the cap, be careful. A large cap can recover some of the charge even after discharge in the bridge. Painful. Fair warning, it is not good for an ordinary cap over 1 mf to be discharged by shorting. The high current flow can breakup metalizing on those types or the internal connections on those with foils. Caps used in camera flashes can take it but still should have a resistor to discharge.
Useful tool...
Chas
RE: Help with Eico 950B knob and pointer - redcsctrike - 06-11-2019
Thank you Chas for the information. My Eico will only reach 495 volts on my multimeter. Definitely not a voltage I want to experience. I bought an 8 x 10 inch Lexan sheet to use for the cursor. I'm not sure if the Eico has the original knob, but if it does, there are no openings for screws. I am unsure how the cursor would have been attached. I do see the knob you mentioned that has holes for the attachment screws. I will purchase one to replace the damaged indicator knob.
Great idea about keeping 1% caps on hand as standards for checking. I think this 950b was re-capped at some point. It seems to be working fine and I get appropriate responses when checking a capacitor. The eye tube is nice and bright. I think I am going to sleeve some of the internal wiring. Lots of bare wire with some very close to the chassis. I get a good eye response when checking value, although without the cursor/indicator, I have no way of reading the value.
I appreciate you taking time to let me know and I will soon make the Lexan indicator.