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 Post subject: Eico 625 Tube Tester circuit overload light/meter adjust
PostPosted: Feb Tue 06, 2018 5:03 pm 
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Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
Hello all,

I have been tinkering with an Eico 625. The trouble is when I adjust line voltage to the center line the circuit overload lamp begins to light dimly, I also hear the transformer hum louder as I increase the line voltage. I see the resistor across the lamp is specd at 3-5 ohms, mine reads 2.4. Would this cause the lamp to light prematurely? I am in the process of checking all the other resistors as well. I have some NOS 6H6 tubes so ill pop that out and test it, but im not sure a marginal 6H6 would cause the trouble. I dont want to burn up the transformer.


Last edited by valley on Feb Wed 07, 2018 5:50 pm, edited 1 time in total.

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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Tue 06, 2018 7:06 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17348
Location: Albuquerque, NM 87123
1st, you need to use an accurate AC voltmeter to check filament voltage. When the meter reads center line then the RMS voltage to the filaments should be correct (6.3 when 6.3 volts is selected). If this is wrong then the line adjust potentiometer may be bad.

The 2.4 ohms across the overload lamp is low; did you remove the lamp before making a measurement?


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Tue 06, 2018 7:49 pm 
Member

Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
Thanks for your reply. I have a small analog multimeter. With the needle pegged to center the voltages read high, 7.5 reads 8v and 25 reads 28. My digitals give a fluctuating reading when taking an AC voltage.

I removed the bulb and got 6.8 which is a bit high according to the schematic.


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 7:07 am 
Member

Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
One other thing I have noticed is the meter needle does not rest at "0," the tip of the needle rests a good 1/4 inch to the left of the 0 line on the scale, approximately the same distance from the center line when voltages are in spec when doing the line adjust. I attempted to adjust the screw but it will not adjust to 0. Is there an internal adjustment for this? After reviewing other pics of Eico 625 tube testers on the web and noting their needles rest on "0" I am thinking this is my problem.


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 7:44 am 
Member

Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
I did check the 200 ohm line adjust pot, I had to de solder one of the transformer leads to get a reading. It reads 200 ohms across and a good smooth transition through the range on the wiper.


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 7:50 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17348
Location: Albuquerque, NM 87123
You may have a damaged meter, or it could have a static charge on the face. First get a damp cloth and clean the face of the meter; it should go back to zero or close to it.


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 7:53 am 
Member

Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
Johnnysan wrote:
You may have a damaged meter, or it could have a static charge on the face. First get a damp cloth and clean the face of the meter; it should go back to zero or close to it.


I hope not. Cleaning with a damp cloth has no effect. Is there a way to mechanically center to zero?


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 7:58 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17348
Location: Albuquerque, NM 87123
That is a 1ma meter; you can test it with a 1.5 volt battery with a 1500 ohm resistor in series with the meter. This should give a full-scale deflection.

Meters can be repaired; it is possible that the adjustment pin in yours has broken off and therefore won't affect the zero setting.


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 8:03 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11444
Location: North of Mpls, Minnesota
The meter should have a clock spring on the front and back. the front one is adjusted so the adjusting tab is centered, then the rear one is adjusted to zero the needle. This takes the hands of a surgeon and the eyes of an eagle to prevent destroying the meter. It may be better to live with it.

Dave


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 Post subject: Re: Eico 625 Tube Tester circuit overload light
PostPosted: Feb Wed 07, 2018 5:48 pm 
Member

Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
This morning I felt adventurous and decided to remove the meter and see what I could do with it. I popped the plastic face off and removed the two screws on the back that hold the movement to the rear portion of the plastic housing, the movement then comes free. As was pointed out there is a small adjustment arm the moves very easily with little pressure, perhaps it is supposed to be tighter and that is why it went out of zero? I zeroed the front adjustment arm and then adjusted the rear until the needle was over the 0 line. The zero seems to hold no matter its orientation, so I think the balance is good. I did not attempt to tighten what I think is the nut that (I assume) applies pressure against the adjustment arm to hold it at zero.

Now when I center the line adjust on line my voltages are right on or very close (within a volt or two on the higher voltages).


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 Post subject: Re: Eico 625 Tube Tester circuit overload light/meter adjust
PostPosted: Feb Fri 09, 2018 3:27 am 
Member

Joined: Jul Thu 18, 2013 11:29 pm
Posts: 92
Location: Madera, CA
Hello everyone,

Does it sound like my issue is fixed? Are there any other calibrations to do on this tester? I checked resistors with them soldered in place and they seem to check out, should I test them out of circuit to be sure?


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